Ammunition Discussion Thread

[Sturgeon]

Let's start this thread off with a an interview with Justin Johnson, the Federal centerfire product manager, coming from Ultimate Reloader:

 

 

 

This interview covers the first year of the Valkyrie, and addresses things like the 90gr SMK's problems, twist rates, barrel life, etc.

[Vicious_CB]

Interesting, Im not too familiar with .224 Valkyrie's development. Its starting to sound like 6.8 SPC/6.8 SPC II's chambering debacle. Just taking a cursory glance at the cartridge, its looks like a niche SPR type cartridge due to its barrel length requirements even then a 18-20" might still not be enough to get the best performance out of a cartridge like this. Would it make a good MG cartridge? Maybe, it would definitely save some weight over a 7.62 NATO gun.

[Sturgeon]

1 hour ago, Vicious_CB said:

Interesting, Im not too familiar with .224 Valkyrie's development. Its starting to sound like 6.8 SPC/6.8 SPC II's chambering debacle. Just taking a cursory glance at the cartridge, its looks like a niche SPR type cartridge due to its barrel length requirements even then a 18-20" might still not be enough to get the best performance out of a cartridge like this. Would it make a good MG cartridge? Maybe, it would definitely save some weight over a 7.62 NATO gun.

 

People freaking out over .224 Valkyrie is the stupidest fucking thing. The cartridge is great, Federal did a great job. People are entitled.

[Vicious_CB]

2 hours ago, Sturgeon said:

 

People freaking out over .224 Valkyrie is the stupidest fucking thing. The cartridge is great, Federal did a great job. People are entitled.

 

Good to know its just some internet bullshit. Just looking at the design I kept wondering where Ive seen those proportions before. I had to dig through the internet to find a picture to confirm it. Ive probably said this before but Im a huge fan of the 5.45 design principals. My dream cartridge was a 5.45 necked up to 6mm throwing 90-100gr VLDs at 2800-2900fps with a stretch in case OAL to achieve that which would be the taboo of breaking the AR15 form factor limitations.  I can understand why they chose .224 projectiles(a reloaders wet dream), my only gripe is its lack of shorter barrel performance. 

 

[Sturgeon]

3 hours ago, Vicious_CB said:

 

Good to know its just some internet bullshit. Just looking at the design I kept wondering where Ive seen those proportions before. I had to dig through the internet to find a picture to confirm it. Ive probably said this before but Im a huge fan of the 5.45 design principals. My dream cartridge was a 5.45 necked up to 6mm throwing 90-100gr VLDs at 2800-2900fps with a stretch in case OAL to achieve that which would be the taboo of breaking the AR15 form factor limitations.  I can understand why they chose .224 projectiles(a reloaders wet dream), my only gripe is its lack of shorter barrel performance. 

 

 

It's not that .224 Valkyrie doesn't have issues. It's that it's been out for just over a year and the worst problems are that the Federal 90gr SMK factory load didn't shoot as good as we'd like for a while, and that some idiot manufacturer fucked up some chamber reamers. I guess people don't remember when 6.8 SPC blew up guns on release because the original factory chamber spec had impossible geometry? Or that there were two completely different and incompatible specs for 6.5 Grendel for years? Or that .300 Blackout to this day fits in .223 chambers, despite the fact that an extra forty five thou in the case could fix this problem? These issues lasted for years and I can come up with equivalents for almost all major rounds out today (remember how 6.5 Creed only had large rifle primer brass for 7 years after release? Remember how .308 only offered 1:12 twist for decades? Remember .30 T/C?). .224 Valkyrie's problems amount to really minor teething issues with a round that's the best design I've seen in years. It's exactly what the market needs and Federal did an amazing job, and people are bitching about problems just because the release was so solid. I've actually had people complain to me that .224 Valkyrie was too available on release so it won't survive these issues because everyone knows about them. Bullshit. Federal did a fantastic job, and I say that because I've never in my life seen a caliber release that was this well organized. They had 17 official partners and 33 total manufacturers on board at SHOT 2018, a year ago.You know why no one knows about .22 Nosler's issues? Because that cartridge is practically dead. Only Nosler offers it (no one else got on board), and it's 1 year older than .224 Valkyrie (and a far worse design).

[That_Baka]

Why .224 isnt considered for USA army next cartrige?

[Sturgeon]

1 hour ago, That_Baka said:

Why .224 isnt considered for USA army next cartrige?

 

Arcane and ultimately unsatisfying reasons.

[Vicious_CB]

Unless it comes in case telescopic, caseless or some weird polymer hybrid the .mil will never buy it.

[Vicious_CB]

Im curious if it would be possible to stick the current 62gr EPR in the case without having excessive freebore jump. Or even what developing a EPR specific for Valk would even look like. 

[Sturgeon]

On 2/10/2019 at 4:43 PM, Vicious_CB said:

Unless it comes in case telescopic, caseless or some weird polymer hybrid the .mil will never buy it.

 

Unless it's the 6.8 GP, the Army will never buy it. At least for now.

 

2 hours ago, Vicious_CB said:

Im curious if it would be possible to stick the current 62gr EPR in the case without having excessive freebore jump. Or even what developing a EPR specific for Valk would even look like. 

 

Yes it would be possible.

 

Oh, you want a Valkyrie-specific EPR with some weird polymer hybrid case, do you?

[Vicious_CB]

On 2/22/2019 at 2:00 AM, Sturgeon said:

 

Unless it's the 6.8 GP, the Army will never buy it. At least for now.

 

 

Yes it would be possible.

 

Oh, you want a Valkyrie-specific EPR with some weird polymer hybrid case, do you?

 

I like this very much. Def not a 62gr, Im guessing an 80gr if you are using the same materials as the current EPR with the same length or more than the current 90gr SMK.

[Sturgeon]

1 hour ago, Vicious_CB said:

 

I like this very much. Def not a 62gr, Im guessing an 80gr if you are using the same materials as the current EPR with the same length or more than the current 90gr SMK.

 

There are multiple versions in multiple weights which are compatible with the Valkyrie. That's an 80gr EPR. Here's another kind:

 

 

That's a 78gr BAT, which is an original bullet designed as a precision training and low intensity combat projectile.

 

 

[Vicious_CB]

Sig's iteration of the Army's 6.8mm wunder cartridge

 

They are claiming a muzzle velocity of over 3000 FPS for a 16″ barrel and 2850 FPS with a 13″ barrel bullet weight not stated. 

 

"As part of the program, SIG has also introduced a new three piece construction hybrid ammunition. It features a Brass case, Steel base and an internal clip to connect the two. So far, they have manufactured 40,000 of their 6.8 x 51 cartridge at their plant in Arkansas and are working on an additional 60,000. Due to its construction, the hybrid ammo offers increased velocities over standard ammunition in the same caliber and can be used in all current weapon systems, unlike some next generation ammunition proposals."

 

 

[Sturgeon]

4 hours ago, Vicious_CB said:

Sig's iteration of the Army's 6.8mm wunder cartridge

 

They are claiming a muzzle velocity of over 3000 FPS for a 16″ barrel and 2850 FPS with a 13″ barrel bullet weight not stated. 

 

"As part of the program, SIG has also introduced a new three piece construction hybrid ammunition. It features a Brass case, Steel base and an internal clip to connect the two. So far, they have manufactured 40,000 of their 6.8 x 51 cartridge at their plant in Arkansas and are working on an additional 60,000. Due to its construction, the hybrid ammo offers increased velocities over standard ammunition in the same caliber and can be used in all current weapon systems, unlike some next generation ammunition proposals."

 

 

 

If it's the Army's standard bullet, it's 135gr.

[Ramlaen]

 

[Sturgeon]

I posted this over at Tony's, might as well post it here. Here's a short explanation of what relative capacity (RC) is, and why it's indicative of cartridge performance:

 

I'm going to do a short demonstration in QuickLOAD since this concept is little understood but very important to the subject of infantry small arms ammunition optimization. We are gonna take three different rounds, all based on the same case, and fire bullets with the same sectional density through each of them, through the same barrel length, and see which one has the highest muzzle velocity. Then, we will measure the Relative Capacities (RC) of each. First, let's take a look at the projectiles:

.224 - 77 gr 
SD = 0.219
Length = 1.274 in

 

.243 - 91 gr
SD = 0.220
Length = 1.341 in

 

.264 - 107 gr
SD = 0.219
Length = 1.370 in

 

I'm going to use the 6.8 SPC case head and a case length of 1.840 inches. Each case is getting modeled in SolidWorks with a 30 degree shoulder and 1-caliber long case neck.

 

Case capacities are as follows:

.224 - 40.3 grains

.243 - 40.7 grains

.264 - 41.2 grains

 

We'll be seating the bullets in the cases to provide as close to identical net capacities as possible, to keep everything even steven. We'll use 20" barrels because... Why not, I guess. Each will be at 57,000 PSI.

 

Here are the results:
 

 

The .224 had a muzzle velocity of 3,088 ft/s, the .243 had a muzzle velocity of 2,991 ft/s, and the .264 had a muzzle velocity of 2,878 ft/s.

 

You know from my two articles on the subject that SD is in the numerator in the Ballistic Coefficient equation (Form Factor is in the denominator). That means, if all of these projectiles are assumed to have the same Form Factor (and in this case the projectiles I based them off of were all very close in FF - though not identical), they will all have the same BC, and that means the best performing of the bunch in terms of drop, wind drift, and flight time will be - perhaps a bit counterintuitively - the .224. Not only that, but hypothetically the .224 could also fire an even heavier bullet with an even higher SD and BC at the same velocity as either the .243 or .264, so it's a win-win.

 

Now, to calculate RC, we need to divide the case capacity by the bore area. Fortunately, QuickLOAD provides bore area to us, so we don't have to calculate it ourselves.

 

.224 bore area: 0.038890 sq in

.243 bore area: 0.045756 sq in

.264 bore area: 0.053723 sq in

 

We have to convert the net capacities to cubic inches next. This can be done by dividing the net capacity in grains H2O by 252.9:

.224:
35.213 gH2O / 252.9 = 0.1392 cu in

 

.243:
35.244 gH2O / 252.9 = 0.1394 cu in

 

.264:
35.283 gH2O / 252.9 = 0.1395 cu in
 

The RCs of each are thus:

.224:
0.1392 cu in / 0.038890 sq in = 3.579 in

 

.243:
0.1394 cu in / 0.045756 sq in = 3.047 in

 

.264:
0.1395 cu in / 0.053723 sq in = 2.597 in

 

So, we can expect that the round with the highest RC will have the best performance in terms of drop, drift, and time of flight (among other characteristics). We can see that this is true, the .224 with nearly 3.6 inches RC does have the highest muzzle velocity for a projectile of a given sectional density. Coincidentally, 3.6 RC is about the same as the 6.5 Creedmoor, and it's usually what I try to shoot for in rounds for applications with barrel lengths 16 inches or longer.

[Sturgeon]

So I've finally gotten sick of it and left Tony's forum (for the, uh... Nth time. I'm like a battered housewife, just keep coming back). One of the things I liked to maintain over there was my Exploring the Design Space thread, which showcased some of my ammunition projects (which are effectively idle distraction for me), and led to some, uh, interesting discussions. So, from here on out, I'll be posting anything that I would have posted there here instead.

 

To kick that off, here's the dumb project I've been working on over the past few weeks. The premise is basically to go full Studler and engineer a dedicated high pressure, high performance round using a case configuration similar to SIG's case design for NGSW, without high regard for recoil and round weight. The only limiting requirement I set for myself was that it had to fit in a PMAG 308 M118, which means using a .473" case head and a 2.830" cartridge overall length. A high muzzle velocity and flat trajectory were priorities for the design. I picked a 16.5" barrel for performance because... I did.

 

The result is actually pretty well engineered! The round fits within standard formats and can accept off the shelf projectiles. At the same time, it skirts compatibility issues with the high pressure ammo and the 6.5 Creedmoor or the .260 Remington. Beyond that, I've given it the most ogive space I can spare, given those constraints, and the result is fairly well balanced. Reasonable energy at distance, good metrics in pH and frag range, etc. The biggest flaw is that it's just not at all efficient by the standards I'm used to. All the same, I'm reasonably proud of it. 

 

I usually name rounds based on whatever's on my mind at the time (I like giving things names, but don't want to spend an hour to find the "perfect" moniker), so read into this what you will. Here's the 6.5x52mm Archangel:

 

It took a few iterations, but what I ended up with is a case with an aluminum base and a brass body, like SIG's, but no internal connecting grommet. So it's sort of a hybrid between SIG and Shellshock's design on that way. If you were to actually produce this kind of case, you'd probably just want to go full steam with the Shellshock design. But I like the way the brass contrasts with the aluminum base, visually.

 

I started with some bullets I had designed for the 6.5 Grendel. The 6.5 Archangel with its 2.060" long case has relatively limited ogive space vs. what I am used to (2.92 calibers or less; I'm used to the 3.24 cals that has become my standard), which made the Grendel bullets an obvious fit, especially if you want to fit within the 2.8" COAL of standard length .308 mags. Actually, much of the case dimensional refinement occurred with these projectiles, and I ended up standardizing on enough ogive space to allow for these Grendel-specific bullets within the 2.8" COAL. The initial Grendel projectile I used was 100gr, which was about the mass I wanted, but it was a couple years old and its shape isn't terrifically refined by my current standards. So I revised it, and ended up with a projectile that had about an 0.907 i7 FF which... Is just "OK" by my standards. This gave a pretty mediocre BC of 0.226 G7, which led me to design a projectile to make use of the full space between the 2.060" case length and the 2.830" COAL for the M118 sized PMAGs. This led to the current bullet with an 0.892 i7 FF, 0.230 G7 BC, and 2.92 cal ogive space.

 

My velocity goal throughout this was 3,200 ft/s from a 16.5" barrel. This is on the "extreme" end of performance for this barrel length. Significant penalties are incurred from just trying to accelerate the bullet to these speeds within such a short length, making achieving velocities like this much harder than the energy level alone would suggest. Fortunately, we're using a high pressure case design and are seeking operating pressures of 70,000 PSI+. With 100gr bullets, velocities almost never dropped below 3,200 ft/s during case development, and we ended up with the new, lower drag bullet firing at a MV of 3,280 ft/s (a round 1,000 m/s in metric). Good!

 

The round itself, I would describe as "balls to the wall". It assumes ammunition weight is not a primary concern. It assumes you have some very effective braking devices (made a little easier by that ALMOST 20,000 PSI MUZZLE PRESSURE HOLY GOD CAN YOU BELIEVE IT???). Performance is... Actually not that good for how extreme the round is, but it's difficult to argue with the resulting drop and drift (both are closing in on 6mm Unified - somewhat better, in fact, once you adjust for barrel length). For energy, the 6.5 Archangel takes 7.62 NATO into a back alley and kicks it in the ribs until it gives up its lunch money. That's with a relatively light bullet, also. At a kilometer, the 6.5 Archangel is throwing a solid 520 Joules, while M80A1 from a 24.8" barrel can't even break 400. 16.5" barrel vs 16.5", we're talking an extra 43% energy at that range. Not bad, all things considered.

Overall, I consider the project not worth pursuing. It'd be a failure, but I don't really feel as though it had any real goals outside of what it was designed to work with. So it met those, I guess. There are much more efficient ways to do the same thing, regardless.

 

 

 

[Sturgeon]

For the daring, a 6.5 Creedmoor version:

 

Velocity is about 80 ft/s lower, but the lower form factor bullet (thanks to additional ogive space), means the energy at 1 kilometer is more than 14% higher than the 6.5x52 Archangel, while the trajectory is almost identical (indeed, at a kilometer drop and drift are both marginally superior). This does a pretty good job illustrating the value of additional ogive space, even versus designs that already seem to have plenty.

[Gripen287]

10 hours ago, Sturgeon said:

This does a pretty good job illustrating the value of additional ogive space, even versus designs that already seem to have plenty.

 

With these long-ogive, EPR-style bullets, how far does the shank of the penetrator extend relative to the cannelure? The steel penetrator and copper slug of M855A1 and M80A1 seem to mate up right at the cannelure for whatever reason. For M855A1 it appears that joint is slightly below the cannelure such that the neck of the cartridge reinforces that joint a bit, but it looks like that joint is slightly forward of the neck and cannelure for M80A1. Is there any sort of limit on how far forward of the neck that this joint can extend (e.g., to provide sufficient structural integrity)? Or is it just a matter of balancing the mass of the components that determines where that joint ends up? 

[Sturgeon]

2 hours ago, Gripen287 said:

 

With these long-ogive, EPR-style bullets, how far does the shank of the penetrator extend relative to the cannelure? The steel penetrator and copper slug of M855A1 and M80A1 seem to mate up right at the cannelure for whatever reason. For M855A1 it appears that joint is slightly below the cannelure such that the neck of the cartridge reinforces that joint a bit, but it looks like that joint is slightly forward of the neck and cannelure for M80A1. Is there any sort of limit on how far forward of the neck that this joint can extend (e.g., to provide sufficient structural integrity)? Or is it just a matter of balancing the mass of the components that determines where that joint ends up? 

 

I don't think it matters. When I design an EPR, I usually try to balance the masses of the two parts at least roughly, but to save time a lot of what I do is iterative based on older works. So some of the relationships are copied over several times from decisions made by me 2-3 years ago.

[Sturgeon]

Oh, one thing that does matter is you don't want too much of the penetrator to be "full diameter" within the jacket, as that increases wear. I believe the reason M855A1 allows a little bit of this is to increase the mass of the penetrator within such a limited space.

[Sturgeon]

 

Relocated the cannelure on the Creedmoor EPR and revised the case dimensions of the Archangel to preserve the non-compatibility. Probably should have done this from the start. Case is now 1.975" long.

[Sturgeon]

Playing around with some dimensional ideas with the composite case design:

 

The case head is redimensioned to eliminate stress risers, and the body is redimensioned with a Weatherby shoulder to mitigate internal anomalies that can cause a bullet to sit off-center.

 

The cartridge itself is a .224 caliber designed off the back of a study I just completed (although it's similar to previous calibers I have designed). Performance is an 81gr bullet at 3,100 ft/s, from a 16.5" barrel.

[Sturgeon]

EPR:

 

[Vicious_CB]

On 6/14/2019 at 1:45 PM, Sturgeon said:

 

I don't think it matters. When I design an EPR, I usually try to balance the masses of the two parts at least roughly, but to save time a lot of what I do is iterative based on older works. So some of the relationships are copied over several times from decisions made by me 2-3 years ago.

 

I heard from a little bird that the mechanism for yaw independent fragmentation has to do with fluid expansion starting in the gap between the penetrator and jacket. Perhaps there is a ideal location to optimize flow into the gap to initial expansion.