Designing A Rifle From Scratch(ish)

[D.E. Watters]

On 9/24/2018 at 9:26 PM, Meplat said:

Now make it in 6.5X55 Swede..

 

Hahaha!

 

(which no kidding, would be a fantastic idea, as 6.5X55 is absurdly underrated..An AR platform using 6,5 Swede would be amazing,)

A Czech company did just that, as well as a 7.5mm Swiss variant.  Google the Luvo Arms LA-11.

[Meplat]

21 hours ago, D.E. Watters said:

A Czech company did just that, as well as a 7.5mm Swiss variant.  Google the Luvo Arms LA-11.

Okay, now I know what I want for Christmas.

[Sturgeon]

Back to work on this. Fooling around with some color, first:

 

[Oedipus Wreckx-n-Effect]

Gonna keep the finger grooves?

[Sturgeon]

2 minutes ago, Oedipus Wreckx-n-Effect said:

Gonna keep the finger grooves?

 

That's just a Hogue AR grip I imported bc I am lazy.

[Belesarius]

Just now, Sturgeon said:

 

That's just a Hogue AR grip I imported bc I am lazy.

At least he's honest.

 

[Sturgeon]

Magazine is now complete:

 

 

[Oedipus Wreckx-n-Effect]

5 hours ago, Sturgeon said:

 

That's just a Hogue AR grip I imported bc I am lazy.

HACK FRAUD

[Sturgeon]

Wrapped up the mechanics of the magazine. There's a ton of reverse-engineering going on with the guts of the magazine (thanks, Magpul!). Two followers are modeled here to illustrate its movement within the magazine.
 

 

Here you can see a sketch of the cartridge stack overlaid onto the magazine:

 

 

There are 33 rounds in that stack; the magazine doesn't accommodate the last two and aaaalllllmost clears the third from last. This makes it a 30 round mag with about 3/4ths of the 31st round's worth of extra space. Notice the generous spring chamber even when the follower is fully collapsed. The idea here is to be similar to an AK magazine and use a super long stiff spring for added reliabilitah.

[Sturgeon]

@Ulric

[Sturgeon]

This design does come with a penalty: Weight. We're currently looking at 192 grams empty (with spring). For comparison a Gen 3 30 round PMag is 139 grams, and a 30 round USGI mag is 113 grams. Oof!

[Collimatrix]

I assume you're handwaving the spring weight, but just so you know, when it comes to coil springs, a long coil spring is weaker.  Making a coil spring long is the same thing as putting a bunch of short coil springs in series, which reduces spring constant.  If you want a coil spring that's both long and generates a lot of force, then the coil material needs to be thicker, which results in an outrageous and gigantic magazine spring.

 

Which I think you already knew, from looking at AK magazine springs.  Just pointing out that there's a further weight penalty for this design choice.

[Sturgeon]

11 minutes ago, Collimatrix said:

I assume you're handwaving the spring weight, but just so you know, when it comes to coil springs, a long coil spring is weaker.  Making a coil spring long is the same thing as putting a bunch of short coil springs in series, which reduces spring constant.  If you want a coil spring that's both long and generates a lot of force, then the coil material needs to be thicker, which results in an outrageous and gigantic magazine spring.

 

Which I think you already knew, from looking at AK magazine springs.  Just pointing out that there's a further weight penalty for this design choice.

 

I measured the weight of one of my AK-74 mag springs and added that to the weight of the complete magazine model. That spring was like twice as heavy as the Gen 3 Pmag spring!

Spent some time this evening finishing up the rear trunnion (which is now aluminum instead of steel):

 

[Sturgeon]

Currently sitting at an estimated complete weight of 3.13 kg  / 6.90 lbs without magazine or gun food.

[Sturgeon]

Gave it coolguy gofast colors:

 

[Sturgeon]

Working on the gas system today:

 

[Sturgeon]

Rifle now has a gas system:

 

Wireframe of the gas system:

 

[Sturgeon]

Two sectioned views:

 

 

 

[Sturgeon]

Clearer labeled diagram of the gas system:

 

[Sturgeon]

I've now done enough work that I can be quite confident in mass estimates. We're sitting at 3.15 kg / 6.94 lb without magazine, ammunition, optics, or accessories. That's with a SOCOM profile barrel. With an A1-profile barrel that drops to 2.96 kg / 6.53 lb.

 

A hypothetical 14.5" lightweight barreled SCAR-L with no sights would weigh about 3.08 kg / 6.79 lb, so that improves my estimation of the rifle somewhat I must admit.

[Sturgeon]

Overtravel is currently just shy of 1.68". Decent.

Cut the vent hole for the gas system:

 

Revised gas system:

 

Weight is now a little less than 3.16 kg / 6.96 lbs.

[LoooSeR]

No BARS? How old school.

[Sturgeon]

Shaved some weight, and sitting at 3.10 kg / 6.83 lbs even with a 5.5:1 mass ratio.

[Sturgeon]

[Sturgeon]

Torx!