Mini-Competition: Sioux Scout Rifle Caliber

[Sturgeon]

We're holding a smaller, lower-effort competition while things simmer down enough for me to reboot the Texas competition to allow more people to participate. Those of you that choose to participate, enjoy.

This competition is intended to be a brief 1-2 week long effort which should require only a handful of man-hours to complete, depending on skill level. Unlike a proper competition, this has one person who's judge, jury, and executioner (me!), to allow the maximum number of competitors. Consider this a brief interlude before the reboot of the Texas competition (which is likely to pick up more or less where it left off). Accordingly, there will be relatively little fluff and editorializing. Contestants will be given a basic setting and a set of requirements with a description of the unique mission needing to be solved. Beyond that, contestants will be responsible for filling in the gaps on their own, to whatever degree they see fit.
 

Programs required: Solid modeling software, ammunition load development software, ballistic calculator, performance estimators (provided)
 

Expected man-hours: 5-10
 

Deliverables required: Image of loaded cartridge and projectile, cutaway or exploded view of projectile or projectile + cartridge, cartridge data sheet, bill of materials (including all component masses and materials), ballistic charts (not required to be in graph form), completed performance estimate sheets, any supplementary materials the contestant chooses to provide.

The competition will be largely conducted via the SH discord, if you're interested please PM me for a link if you don't already have one.

BEGIN FLUFF

After the War, the Great Plains became virtually cut off from the rest of the former United States. Governments fractured into small polities based around towns and cities, as local populations realized they no longer were enfranchised as part of a larger economy and logistical network. State governments began to be seen overwhelmingly as distant meddlers who offered nothing in return for their interference in local politics. The area around the Black Hills was no exception. The states of South Dakota and Wyoming disintegrated quickly once the Federal Government of the United States no longer took a direct role in state affairs. A loose government formed around Rapid City, supported by strong manufacturing jobs, traders, and a large ammunition plant that could support paramilitary operations ranging around the Black Hills region and securing the roads that remained passable. Due to this, their influence expanded well into Eastern Wyoming and north to Southeast Montana and North Dakota. The emerging Dakota Union became the primary, if thinly spread, force in the northern plains region. Their most famous agents would be the Sioux Scouts.



Unlike most pre-war infantry forces, which operated as part of large combined arms units in a highly tiered structure, the Scouts are highly independent light infantry. Often, Sioux Scouts will travel hundreds of miles unsupported in units as small as pairs, or even the occasional single Scout. While on patrol, they are responsible for their own sustenance and upkeep, foraging for food and shooting with their rifles what they need to survive. For the moment, there are no other organized military forces in the region, and Scouts are tasked primarily with maintaining contact, trade, and awareness of the peoples living inside the Northern Great Plains, and the hills to the West. As part of their duties, they are sometimes called to settle disputes, mete out justice, or are even permanently stationed in affiliated regions to maintain law and order. In times of war, they function in larger units as an army to protect Black Hills from incursion, but this hasn't happened in many decades. There is no distinction between "officers" and "enlisted" in the Sioux Scouts, but there is a basic hierarchy, and Scout pairs will often have a subordinate and a superior. In times of greater trouble, Scouts are also expected to marshal and lead local forces in the local defense. Generally, Sioux Scouts travel on foot or on horseback. They are substantially made up of Indian peoples, although any residents of the Dakota Union may join the all-volunteer force.

 

 

Currently, the Sioux Scouts are armed with a motley assortment of both manually-operated and semiautomatic rifles in various calibers. The Sioux Scouts have requested a new semiautomatic rifle to replace these, and it has been determined that they require a new caliber to go along with it, hopefully phasing out the assorted legacy calibers in the process. Thanks to the plant in Rapid City, this is a very feasible request for the Dakota Union (and helps sustain jobs in its largest city). You are an engineer at the Rapid City plant, tasked with creating a report on what the new caliber's characteristics should be. Resources, testing facilities, and reams of research are made available to you. The year is 2221. Get to work.

END FLUFF

 

The new round must:

1. Produce no less than 700 ft-lbs at 600 yards.

2. Penetrate twenty-four 1/2" pine boards at 600 yards (equivalent to a lethal penetrating shot on a quartered buffalo).

3. Drop no more than 96 inches at 600 yards (2.6in sight height, 100yd zero, 59.0F temperature, 29.92in Hg pressure).

4. Drift no more than 36 inches at 600 yards (2.6in sight height, 100yd zero, 59.0F temperature, 29.92in Hg pressure, 10mph 90 degree crosswind).

5. All performance requirements must be met at 200 ft/s below the spec velocity, except the 600 yard energy requirement, which can be met at 500 yards at -200 ft/s, instead.

6. Produce pressure no greater than 52,000 CUP (brass cased) or 50,000 CUP (steel cased).

7. Use a projectile composed only of any combination of the following: Copper alloy, bronze alloy, lead alloy, iron alloy, steel alloy, tin alloy, nickel alloy, and/or zinc alloys. Titanium, tungsten, aluminum, magnesium, and other exotic metals are not allowed.

8. Minimum magazine capacity must be 20, with a stack height no greater than 5 inches.

9. Cartridge overall length may not exceed 2.8 inches.

10. Cartridge recoil from a 10lb weapon may not exceed 12 ft-lbs.
11. Cartridge must meet performance requirements from a 22" barreled weapon.

12. Cartridge must cost as little as possible.

You are provided with calculators to use to estimate these values for the competition. For trajectory, drift, and energy, you must use JBM Ballistics calculator here. Internal ballistics must be estimated via the Powley Computer (just check the pressure box and enter 52,000 CUP for brass or 50,000 CUP for steel). Also please see my guidelines for modeling steel cases here. The pine penetration value must be calculated with this spreadsheet, and the recoil energy with this spreadsheet. For the purposes of this competition, cost per round is determined solely by the materials used. Please reference the material cost sheet here. If you do not already have a solid modeling program, you can use Google SketchUp for free. @Toxn has a lot of experience with it, you might ask him.

[Toxn]

Is this going to be one of those ones where, if you follow the requirements dilligently, you end up with something fast, in the 5-6mm range, shooting a long, skinny bullet?

 

Because I've already specced out a 10mm fat fuck bullet based on an elongated 9x39mm, and I'm going to complain mightily to the board if my MANSTOPPER BIG BORE MAGNUM doesn't get the nod

[N-L-M]

On 5/25/2020 at 7:30 PM, Toxn said:

you end up with something fast, in the 5-6mm range, shooting a long, skinny bullet?

By a strange coincidence, this here is the .22 Rapier.

 

[Toxn]

14 minutes ago, N-L-M said:

By a strange coincidence, this here is the .22 Rapier.

 

Boooooooooring

[Toxn]

Having now delved into this issue a bit, the bias of the judging committee becomes clear. They are determined to snuff out the manly, big bore cartridge and replace everything with weak, womanly micro-bullets!

 

Well, two can play at that game. Here is the 5x58mm PoS (Poodle Shooter); a cartridge designed specifically to wound small animals and burn up barrels:

We considered other names: the 5x58mm WaNK (Wound and Not Kill), the .197 StFU (Stupid-small, Fast and Useless), the 19-55 Shamebringer and so on. We would be happy to elaborate on these monikers further should the committee so require.

 

The bullet (barely more than a pellet) is turned brass, because we cannot imagine anyone wanting to make the fiddly tooling to jacket it. The case is lacquer-coated steel, so that soldiers can waste ammunition more easily without so much as having to stoop to pick up expensive brass. Proof that it fulfils the despicable requirements of the biased commitee is provided below (OOC note: the BC is based on the Berger 6.5mm 140gn VLD bullet, using 0.307 G7 BC):

 

This includes the lower-velocity requirements:

I think we scarcely need to provide proof that such a pathetic round meets the recoil requirements - simply give weapons to women and children and ask them for their opinion (OOC note: 3.8186). Penetration is... uh, acceptable (OOC note: 27 1/2" pine boards, stopping in the 28th at 600y using the lower-velocity test cartridge).

 

Moving on: as to the economy of the round, the calculated value is 8.77 cents. This proves that, even when shooting such microscopic bullets, there is simply no value for money over the venerable M80! Given how expediently we intend our offering to be produced (because we intend to warn our government, not rob it), we cannot imagine that our competitors will do anything more than burn through tax-payer's money in their feckless pursuit of speed over power.

 

A final word: know that we, the designers, have seen through this comical charade and are one step ahead! We have now bought into a barrel making and rifling tooling company, in the expectation of making a fortune on future government contracts for worn-out barrels when this contract is inevitably handed to one of the small-bore "iconoclasts" that litter this great city.

 

In conclusion; we hope that the government of our great Dakota Union soon sees the light and kicks out the charlatans running this rigged competition out. Until then, we offer the 5x58mm PoS as a warning, and a plea to return to a more sensible procurement approach based on the stopping power of big bullets.

 

Edit: so, as @Sturgeon pointed out, I done goofed up with the bullet's BC. When you use something more appropriate, the bullet actually fails on the energy requirement. Which is just more proof of the inferiority of micro bullets! Etc etc.

[Sturgeon]

8 hours ago, Toxn said:

Having now delved into this issue a bit, the bias of the judging committee becomes clear. They are determined to snuff out the manly, big bore cartridge and replace everything with weak, womanly micro-bullets!

 

Well, two can play at that game. Here is the 5x58mm PoS (Poodle Shooter); a cartridge designed specifically to wound small animals and burn up barrels:

We considered other names: the 5x58mm WaNK (Wound and Not Kill), the .197 StFU (Stupid-small, Fast and Useless), the 19-55 Shamebringer and so on. We would be happy to elaborate on these monikers further should the committee so require.

 

The bullet (barely more than a pellet) is turned brass, because we cannot imagine anyone wanting to make the fiddly tooling to jacket it. The case is lacquer-coated steel, so that soldiers can waste ammunition more easily without so much as having to stoop to pick up expensive brass. Proof that it fulfils the despicable requirements of the biased commitee is provided below (OOC note: the BC is based on the Berger 6.5mm 140gn VLD bullet, using 0.307 G7 BC):

 

This includes the lower-velocity requirements:

I think we scarcely need to provide proof that such a pathetic round meets the recoil requirements - simply give weapons to women and children and ask them for their opinion (OOC note: 3.8186). Penetration is... uh, acceptable (OOC note: 27 1/2" pine boards, stopping in the 28th at 600y using the lower-velocity test cartridge).

 

Moving on: as to the economy of the round, the calculated value is 8.77 cents. This proves that, even when shooting such microscopic bullets, there is simply no value for money over the venerable M80! Given how expediently we intend our offering to be produced (because we intend to warn our government, not rob it), we cannot imagine that our competitors will do anything more than burn through tax-payer's money in their feckless pursuit of speed over power.

 

A final word: know that we, the designers, have seen through this comical charade and are one step ahead! We have now bought into a barrel making and rifling tooling company, in the expectation of making a fortune on future government contracts for worn-out barrels when this contract is inevitably handed to one of the small-bore "iconoclasts" that litter this great city.

 

In conclusion; we hope that the government of our great Dakota Union soon sees the light and kicks out the charlatans running this rigged competition out. Until then, we offer the 5x58mm PoS as a warning, and a plea to return to a more sensible procurement approach based on the stopping power of big bullets.

 

Typical fudds! They can't do ballistics at all! They scaled down the 140gr Berger without adjusting its BC!

[Toxn]

7 hours ago, Sturgeon said:

 

Typical fudds! They can't do ballistics at all! They scaled down the 140gr Berger without adjusting its BC!

Small boolit too small for wind catch so bal...balleee...bee-see no matter

[Gripen287]

Is there a specific deadline for this competition? Progress on the .246 Sweet Pea has been good so far, but there is still room for improvement.  Also, can we expect any guidance as to how the requirements will be weighed against each other?

 

 

 

[Sturgeon]

34 minutes ago, Gripen287 said:

Is there a specific deadline for this competition? Progress on the .246 Sweet Pea has been good so far, but there is still room for improvement.  Also, can we expect any guidance as to how the requirements will be weighed against each other?

 

 

 

Deadline is basically "when everybody looks like they're done", but I don't expect it to take longer than a couple of weeks.

I asked on the discord about whether I should release a grading rubric and they preferred a more freeform approach. So I intend to see what we get and take it from there.

Also, they determined that there would be a $20 prize for the winner.

I release information and provide assistance regularly on the discord, so feel free to request a link and hop on.

[Gauntlet]

Just out of curiosity. Will the results made public on the forums, including all the details? I am in now way to participate but nonetheless find it interesting to read about it.

[Sturgeon]

28 minutes ago, Gauntlet said:

Just out of curiosity. Will the results made public on the forums, including all the details? I am in now way to participate but nonetheless find it interesting to read about it.

 

Yes they will.

[Sturgeon]

I forgot to put this in the OP, apparently, but I am also requesting that competitors provide IGS or STEP files of their submissions, so that I can create a "family photo".

 

Also for the record, IGS files of each component rather than an assembly would be good. Also list all the materials for each component. 

[Sturgeon]

I didn't elaborate much on what all the deliverables needed to be exactly, but think "reproducibility"

[Sturgeon]

So I did not adequately explain how to derive BC from the JBM chart. That's my bad. It's too late to change it, since most of you are basically done.But for the record, you measure it over 500 yards. First, you guess the BC, make a ballistics chart, take the Machs at 0yd and 500yd and then average all the BC figures covering those mach numbers on the drag estimation chart.

e.g., starting mach is Mach 2.64, ending mach is Mach 1.92, you average all the BC results from Mach 1.5 to Mach 3.

If you have already submitted it, don't worry. If you're still in the process of doing calculations, you can use this to properly adjust it.

[Sturgeon]

I am seriously considering a phase 2, where I give contestants feedback and they go back and revise, before a winner is chosen. If the contestants are game, we'll do that.

[N-L-M]

The SCHV shill department of Black Hills is proud to present the .22 Rapier!

Featuring a .224, 83 grain copper-washed steel jacketed bullet, a steel case, and enough powder to sent said bullet downrange at above 2900 fps, this cartridge is the ideal choice for scouts.
by the wisdom instilled from the studying of the works of the ancients, our chief Shaman was blessed with a revelation - once a bullet is in flight, it may not gain energy, only lose it. Therefore, it makes no sense to choose any bullet shape but that which experiences the least drag, and as such a boat tailed  Von Karman ogive bullet approximately 6 calibers long was chosen.
In order not to consume any expensive copper, and considering the low expected lifetime ammunition throughput of any individual Scout rifle, mild steel (copper washed) was chosen as the prime working material, except the lead core.

The performance, while not outstanding in the criteria measured, is acceptable; where the cartridge really shines is cost, both monetary and weight - with a cost of merely 4.56 C a round, its a steel steal, and the overall weight of 220.5 gr means it is approximately 40% lighter than the historic 7.62 NATO and equivalents in current service, thus allowing to greatly reduce the burden carried by Scouts without compromising their mission effectiveness; and, should they need their weapons, they may rest assured that their bullet  is accurate (exceeds drift and drop specifications), powerful (exceeds energy and penetration specs) and quick (exceeds recoil requirements by a factor of 3). 
Not only do the Scouts get a round which on a 1:1 basis exceeds current issue on every parameter, they get a ratio better than 1:1! with a rim diameter of 0.4", the round may de stacked in a double column of 24 rounds without exceeding the 5" stack limit imposed by maximal magazine dimensions, an improvement of 20% over that requested.

 

The round also features growth potential; the large bullet and generous ogive space mean plenty of room for other loadings, and the steel case provides growth capacity to more pressure resistant (if more expensive) brass cases for specialty loads.

 

In short, this round presents all that's best in pre-war small arms ballistics, providing a good answer to the needs of the scouts of today, tomorrow, and perhaps also the day after.

 

Reduced velocity:

 

Full velocity:

 

 

 

[Curly_]

I present my own cartridge in this competition, the .224 Zoomer Magnum, also known as the 5.7×47mm. In order to increase the number of rounds that each individual Sioux Scout can carry, I felt that a small caliber, high velocity cartridge would be in order, one that would have light recoil while also meeting (if not exceeding) the requirements set forth. I originally started off with a 1.775" case length (said case was designated as "No. 1"), but the case capacity was found to be woefully insufficient for the desired muzzle velocities. A second cartridge case (designated "No. 2"), with the length increased to 1.875", was found to be just the right amount of capacity needed. Two projectiles were also to be designed. The Type A projectile would be lead-cored with a thick, gilding metal clad steel jacket to prevent fragmentation in soft tissue, enhancing its penetration and preventing lead contamination in wild game taken as food. A small cup would seal off the lead core to prevent it from being squeezed out of the base of the projectile. A more ambitious, cost-reduced Type B projectile was also conceptualized, consisting of a gilding metal clad steel jacket, a mild steel core, and an overall reduced weight compared to the Type A. However, the Von Karman ogive required for this projectile proved to be an real pain in the ass to model with what limited tools were available, and for the sake of my own sanity, the Type B was dropped in favor of the tangent-ogived Type A.

 

Type A projectile, cross-sectioned. Projectile weight was calculated to be 79.5 grains, with a G7 BC of 0.265. Note the metal cup sealing off the lead alloy core.

Spoiler

 

Complete cartridge, Type A projectile, No. 2 case. The case itself is lacquered steel. Total cartridge weight is approximately 13.66 grams, and the total materials cost is about 5.04680378 cents.

Spoiler

 

Load data. Recoil is approximately 3.38 ft-lbs from a 10 lb weapon.

Spoiler

 

External ballistics, with nominal muzzle velocity. Penetration into pine is approximately 16.52 inches at 600 yards, rounded down to the nearest hundredth of an inch.

Spoiler

 

External ballistics, with muzzle velocity reduced by 200 ft/s. Penetration into pine is approximately 15.40 inches at 600 yards, rounded down to the nearest hundredth of an inch.

Spoiler

 

[Gripen287]

Recognizing that our Sioux Scouts are expected to operate in the diverse environments of the Dakota Union, the engineers at our Rapid City munitions plant have developed a new cartridge to aid the Scouts in carrying out their duties. That cartridge is the .246 “Sweet Pea.”  We believe that Scouts of today and tomorrow will put this cartridge to good use in the granite hills, wooded valleys, expansive prairie, and increasingly vibrant and prosperous towns of the Dakota Union.

 

While some Scouts may judge its performance at 600 yards as merely being adequate, Scouts skilled in the arts of stalking and evasion will appreciate the Sweet Pea’s light weight, energy at closer ranges, extremely flat trajectory to 300 yards, and outstanding terminal performance on targets both large and small.  A partially-exposed, steel “arrowhead” penetrator conveys an intimidating appearance that hints at the devastating wounds the bullet is capable of, particularly at closer ranges.  It is true that the Sweet Pea’s meplat may be larger than that of some its target-shooting oriented contemporaries, but the Sweet Pea’s wider meplat aids in penetrating into the target rather than merely glancing off it when striking at an oblique angle.  Stress relief channels pressed and cut into the bullet’s bearing surface help ensure long barrel life despite the Sweet Pea’s deep penetrating steel core.  The middle channel also promotes generation of larger, deeper penetrating jacket fragments in tissue.  Even though the Sweet Pea is optimized to end fights quickly and humanely kill game at the ranges our Scouts find themselves having to use their rifles most often, the Sweet Pea’s relatively long ogive and aerodynamic boat tail ensure that our Scouts will not have to shy away from taking shots out to 600 yards and beyond.  Official magazine capacity is 22 rounds, although enterprising Scouts have been known to find room for 23.
 
Moreover, even actuaries far from the frontier can take comfort in the Sweet Pea’s economy.  At a mere 5.70 cents per round, the introductory 88 grain “ball” round is largely constructed from mild steel components, save for its bullet jacket, and therefore, the Sweet Pea will not overly impede the ongoing effort to rebuild the Union’s electrical infrastructure.  Furthermore, the near total elimination of lead in the Sweet Pea’s construction will eliminate the expensive and onerous precautions that the workers in our munitions plants must endure when working with this toxic substance.  Our engineers are optimistic that the cartridge will be entirely free of lead if efforts to redevelop the lead-free primers of an earlier time are successful. 

 

For additional information, please consult the materials provided.  We hope that you too will discover why this new cartridge truly is a “sweet pea.” 

 

.246 Sweet Pea Data Sheet

 

.246 Sweet Pea Renders and Performance Estimates

 

 

 

 

 

 

 

Edited May 31, 2020 by Gripen287
Humor

[Toxn]

Friends, rejoice!

 

After a long stint at the Dakota Union reeducation camp I have returned. There the evil blackguards who preach the word of small, weak bullets tried to convert me to their blasphemy. But I was too cunning for them - I learned their ways and have returned to turn their secret fires against them!

 

Here is my creation, the shining spawn of my mind. Behold, the 7x48mm FGM2!

Although still a bit petite for those amongst us who still follow the true creed of big, girthy, manly-man bullets, it shall serve as a dagger thrust into the heart of the snake that is the second joint committee for cartridge development. For it meets, nay exceeds the requirements of their grotesque mockery of a competition. Now, truly, the scales will fall from the eyes of the people as they are forced to test it and admit its might!

 

And here is the proof:

 

And even at lower velocities, it still almost very nearly juuuuuuuust doesn't make the requirements:

 

And the news only gets better from here! The recoil is low enough even for the atrophied shoulders of the testing committee (10.49 ft-lb). The penetration into pine boards easily exceeds requirements even at the lower velocities (26 pine boards at 600y at the lower test velocity, 29 at the higher velocity). And the cost is fantastically cheap (5.63c) thanks to the use of an annealed, copper-washed mild steel mono-bullet and a lacquered steel case. Truly this is an expedient cartridge that every soldier can take into battle aplenty, to distribute to his foes liberally. And best of all, the use of a long, finely-profiled bullet (OOC note: dimensions taken from here and properly adjusted this time) means that there is plenty of volume for specialty loads (incendiary, armour piercing and so on) that can be ballistically matched to the standard round.

 

My friends, it truly feels good to be able to say this: our great Dakota Union now has a cartridge fit for a man.

 

Edit (OOC note): so I'm a dumb-dumb in more ways than one, and needed a lot of background assistance from @Sturgeon to put together something that actually made requirements (kinda, sorta, almost). So a big thanks to him for taking the time to answer all my questions and provide feedback.

[Su-57 Flapjack]

Comrades, co-conspirators, people of Big Sky Country!

 

I present to you the culmination of extensive research done in the depths of our underground laboratories, including the construction of a seven-hundred-meter tunnel for the verification of ballistic data.

 

 

The .257 FLAP, or by its metric designation 6.35 × 50 mm FLAP, is a new rifle cartridge delivering the performance required to kill buffalo out to 1400 yards, as much accuracy as your rifle can get out of it, and much much more! The round's slippery ogive -- off the design of von Kármán himself -- provides for excellent aerodynamics, and the heavy-for-caliber projectile holds on tight to every last foot-per-second, staying supersonic well past a kilometer.

 

The 0.257" diameter projectile weighs 132 grains and is 1.37 inches long, or approximately 5.3 calibers. All-up length is 1.98 inches.

 

Here is the printout of our hypercomputer's performance estimate - most of the development costs so far have been in replacement vaccuum tubes.

 

 

Here the performance at nominal velocity can be seen - impressive! High energy!

 

 

Even with a 200 fps velocity penalty, it ZOOOOOOMs.

 

Recoil energy is a measly 9.13 lb-ft. Pine penetration is much more than adequate, but reaches at least 48 cm at 600 yards even with the velocity penalty.

 

Cost per round is 7.884 cents, which is cheap enough, amirite?

 

Happy shooting, to all who will choose this superior, medium-bore, heavy-bulleted monstrosity!

[Icarus]

!!!Unofficial submission disclaimer!!!

 

 

Having recently uncovered an survival shelter sealed in perfect condition, with intended occupant's remains found near the entrance, we have access to more accurate pressure testing, and prediction technologies of the old world.

 

Taking advantage of this development boon, we have developed the 6x51mm Sioux Scout cartridge based on the following methodology.

 

Scouts will be shooting primarily at game animals, or ruffians, but occasionally more sturdy animals or targets - therefore a mid-size caliber that we definitely don't have a predisposition for, and certainly haven't found accurate data and a stockpile of reverse engineer-able projectiles for, should be selected. The reason for the use of the smallest and lightest viable bullet is that a harder target like bear, moose, bison, etc may take multiple shots but are likely to be a significantly less frequent ammunition expenditure than marksmanship and skill maintenance training, border patrol, or other police action uses. Given the available scavenged expertly developed projectiles, and development software, we decided to pursue the lightest viable bullets to meet the requirements set forth by the program, which ultimately this lead us to a selection of .224" and .243" 85-105 grain projectiles. We settled on a 95gr secant ogive design of traditional copper jacket lead core construction for both .224" and .243" bullet diameters and noticed that the wider bullet was more powder-efficient, would have a more modest relative capacity and barrel life, and likely be slightly easier to manufacture.

 

The case we would like to be brass, but for production cost reasons, we concede steel construction but insist on small magnum rifle boxer primers. Sample image is provided in beautiful brass color.

 

(I am stealing Gripen's characteristics format because it is good and I am lazy)

 

Cartridge Characteristics: 

• Bullet Diameter: 0.243

• Neck Diameter: 0.267

• Shoulder Diameter: 0.3346

• Base Diameter: 0.355"

• Rim Diameter: 0.355"

• Rim Thickness: 0.0591

• Case Length: 2.025

• Overall Length: 2.750"

• Case Capacity: 34.3 grains H2O

• Relative Capacity: 2.99 total, 2.62 usable

 

• Recommended Rifling Twist: 1-in-7” (152.4 mm)

• Primer Type: Small Rifle Magnum Boxer

• Maximum Pressure: 50,000 CUP ( ~ 59,000 psi)

 

• 5” Magazine Stack Height: 27 cartridges 

 

Loaded Cartridges

• 95gr VLD loading:

  • 27.1 gn CuZn5 jacket;

  • 67.9 gn lead core

  • 28.5 gn propellant charge of IMR 4895

  • 75.3 gn mild steel case

  • 3.9 gn small rifle primer

  • 202.7 gn complete round 

  • 5.1 cents material cost, complete round

 

Additional projectiles are currently under salvage operations development.

 

Representative Performance* (95gn VLD Nominal Loading)

• Muzzle Velocity (22” barrel): 2849 ft/s

• Muzzle Energy (22” barrel): 1719 ft-lb

• Ballistic Coefficient (G7): 0.249 

• Form Factor (G7): 0.982 - 0.962

• Drop at 600 yd: 77.5 in

• Drift at 600 yd (90°, 10 mph): 27.7 in

• Recoil (10 lb weapon): 4.84 ft-lb

• Penetration into pine at 600 yd**: > 15 in 

 

Representative Performance* (95gn VLD Degraded(-200fps) Loading)

• Muzzle Velocity (22” barrel): 2649 ft/s

• Muzzle Energy (22” barrel): 1486 ft-lb

• Drop at 600 yd: 93.1 in

• Drift at 600 yd (90°, 10 mph): 31 in

• Recoil (10 lb weapon): 4.38 ft-lb

• Penetration into pine at 600 yd***: > 14 in 

 

* 2.6 in sight height, 100 yd zero, 59.0 °F, 29.92 in Hg pressure

** when striking at 1795 ft/s or greater

** when striking at 1665 ft/s or greater

Relevant ballistic data

Case head detail

Case Dimensions

Our valuable scavenging find

 

 

[Sturgeon]

Current leaderboard. Feedback to follow.
 

1. @Toxn

2. @N-L-M

3. @Curly_

4. @Gripen287

5. @Su-57 Flapjack

[Sturgeon]

I want to be clear that Gripen did not get 4th for lack of effort. The care and effort that went into his submission was the absolute best among all entrants, so far.

[Sturgeon]

Feedback. I expect everyone to read each section since feedback to other entries may prove useful in optimizing your own.

 

@Toxn
 

1. The projectile design is one of the most innovative and goal-oriented of all the submissions. A solid steel projectile could provide major benefits, chiefly in terms of cost and target penetration. Despite being much larger in caliber and using far more materials by mass, the 7x48mm ended up cheaper per shot than the .246 Sweet Pea. The primary disadvantage is likely to be barrel wear, but the submission cleverly includes a half-thousandth reduction in the diameter of the projectile versus the groove diameter, which should alleviate this somewhat. It is possible that further modifications may be needed to achieve acceptable wear and accuracy characteristics, but the simplicity of the current design is highly admirable.

2. The chamfer at the interior root of the case wall should be replaced with a radius of approximately 0.040".

3. The projectile ogive radius should be decreased to match the von Karman shape as closely as possible, to reduce drag. Alternatively, a true VKO ogive could be used.

4. The meplat diameter is excessive, at approximately 0.22 calibers. A meplat diameter of 0.15 calibers would reduce drag while still being highly practical to manufacture for a monolithic bullet.

5. A rounded meplat would be both easier to form and lower drag, given the projectile construction.

6. The given projectile length of 1.5" appears to be too long to give the stated projectile weight.

7. A reduction in caliber would allow for better performance, increased sectional density, and potentially reduced cost.

8. Hardening the tip of the projectile would allow an extremely inexpensive semi armor piercing option.

9. -80000 million points for metric.

@N-L-M
 

1. The ballistics are very good. Well done copying my hard work!

2. The flash hole is excessively deep for a steel case. A flash hole depth of 0.060" would be more appropriate, and would allow an increase in case capacity or decrease in case size.

3. The cartridge rim is excessively thick. 0.060" is more than sufficiently thick. Reducing this thickness and the total groove height correspondingly would allow the maintenance of case wall thickness while allowing an increase in case capacity or decrease in case size.

4. There is no visible lock between the jacket and core. Are they bonded?

5. You could choose to tighten up the case taper and shoulder angle to 25-30 degrees and 0.5 degrees, respectively, without ill effects besides a somewhat higher case rejection rate. Your choice.

6. Ogive space should be increased by 0.010" so that seating depth tolerance is increased to a total of 0.020".

7. The radius at the interior root of the case wall is probably excessive. An 0.040" radius would be sufficient while increasing capacity somewhat.

@Curly_
 

1. Typically ballistic lead is at least 3% antimony or tin, to increase hardness and thermal stability. Since you assumed elemental lead for the slug, this results in a slight projectile weight decrease from 79.5 to 78.4 grains when using 3% antimony lead.

2. The thickness of the brass at the case mouth and shoulder is somewhat excessive. It could be reduced to 0.0122" without issue.

3. The extractor groove could be expanded slightly to allow a larger extractor.

4. The case rim could be thickened slightly to 0.060".

5. The base plug on the projectile is additional complexity that is probably unnecessary. Although it would help prevent lead vaporization.

6. The meplat is 0.182 calibers in diameter, which is not considered excessive, but which could be reduced to approximately 0.12 calibers without negative manufacturing penalty but with a potentially significant benefit to drag reduction.

7. Calculation of the i7 FF/G7 BC from the JBM charts was not done properly. For a round with this muzzle velocity, the correct method is to average all values (either BC or FF to derive that property) from Mach 3 to Mach 1.5. Doing this results in a calculated G7 BC of 0.2095 vs. 0.216 used.

8. Ogive space should be increased by 0.013" so that seating depth tolerance is increased to a total of 0.020".

@Gripen287
 

1. There was a discrepancy in the cartridge case mass. Worksheets stated the mass was 180 grains, when in fact it measured at 123.6 grains.

2. A 35 degree shoulder angle is considered "high risk" for a steel case.

3. The steel case, as far as the submission showed, was made of uncoated mild steel. This would corrode extremely easily. Some kind of anti-corrosion coating is recommended.

4. The projectile features several details which would together dramatically increase drag. The gap between the penetrator and jacket is very broad, and the jacket sports three extremely deep grooves which both challenge manufacture and add substantial projectile drag. The plus side of these grooves is reduced barrel wear, but it is estimated that these features combined would increase drag by up to 25% (5% per groove, plus 10% for the EPR gap, according to previous test results). It is recommended to eliminate these grooves and close or eliminate the gap between the projectile jacket and the penetrator. The chamfer along the base edge of the boattail is unnecessary and would somewhat increase drag. The meplat is 0.178 calibers in diameter, which is not considered excessive, but which could be reduced to approximately 0.12 calibers without negative manufacturing penalty but with a potentially significant benefit to drag reduction.

5. The penetrator is described as being made of low carbon steel. This compromises the penetrative ability of the EPR-style projectile and it is recommended to switch to a tool steel.

6. Fragmenting EPR style bullets have not been demonstrated as reliable killers against buffalo, let alone EPRs as small as 88 grains.

7. Boattail length of ~0.835 calibers is considered good.

8. Jacket thickness of 0.024" is considered excessive for an EPR-style bullet, much better suited to a non-fragmenting FMJ-style bullet. A jacket thickness of between 0.017-0.019" is considered more suitable for the EPR type.

9. The detail and effort that went into the models and the submission overall is considered excellent.

10. Calculation of the i7 FF/G7 BC from the JBM charts was not done properly. For a round with this muzzle velocity, the correct method is to average all values (either BC or FF to derive that property) from Mach 3 to Mach 1.5. Doing this results in a calculated G7 BC of 0.2095 vs. 0.216 used.

11. The caliber of 0.2465 is considered odd, and not compatible with existing barrel stocks. If feasible, a change to 0.243 caliber would be preferred.

@Su-57 Flapjack
 

1. The ogive of the .257 FLAP does not appear to be a Von Karman ogive. It looks like the curvature of the equation is inverted. Please see the embedded comparison between the FLAP ogive and a real von Karman ogive (light blue):


 

2. The .257 FLAP projectile has both an open tip and an open base. There appears to be no reason for this. It adds manufacturing difficulty without adding value. A reverse-drawn jacket OTM would be far better.

3. There appears to be no justification for the 0.85 i7 FF, although it is relatively close to the calculated 0.858 i7 FF I got from JBM.

4. Flash hole diameter could be increased to up to 0.080" wide. to allow a greater flame channel.

5. Groove depth (outer minus inner diameter) could be increased by 0.007" to allow a larger, more robust extractor.

6. There is not enough of a radius at the interior root of the case wall (radii there should be approx 0.04").

7. Nominal projectile weight is off from measured projectile weight by nearly 10 grains (131gr nominal vs 140.95grs measured). 

8. The jacket is far too thin. 0.017" is considered a solid minimum for gilding metal, while the jacket of the .257 FLAP is just 0.009". This will result in in-barrel jacket rupture and disintegration of the projectile before exit from the muzzle.

9. There is a disparity in the proposed case capacity and the measured case capacity of the round (0.54 grs H2O). This, combined with the disparity in the projectile weight, results in a discrepancy in the muzzle velocity of nearly 100 ft/s. Fortunately, even with this performance, the round meets the requirements even at an additional -200 ft/s velocity.

10. Neck length is 9mm, and this is considered excessive. Consider reducing the neck to 0.9-1.0 calibers. Oddly, this long neck is not used to set the neck-shoulder junction back from the end of the shank of the bullet, which is the usual purpose of long necks.

11. The projectile is seated too deeply in the case. Maximum OAL should allow the projectile to be seated 0.020" deeper than the maximum without the ogive sinking below the case mouth. However, the .257 FLAP already has its ogive seated 0.001" below the case mouth, at stated max OAL.

12. The cost of the .257 FLAP significantly exceeds those of other candidates due to its use of a brass case and a relatively large quantity of propellant. Consider using a steel case to reduce material costs.

[A. T. Mahan]

I'll be submitting a cartridge once I finish working it up, probably by the end of the week. Currently I am estimating in excess of 900ft-lb and 32 pine boards at 600 yards, and above the transonic regime to 1,000 yards. I have not downselected fancy bullet designs between a monolithic gilding metal OTM and a reverse-base-drawn exposed penetrator AP design. I have high hopes for this cartridge, and believe that it will prove quite successful.