Many projects have come and gone since the last time I posted here.

Figured there might be some interest in the current effort. M4 retrofit for 6.5 Grendel w/ composite case, including new bolt, barrel, barrel extension, carrier, and magazine.

Recently got done with some FEA on the new bolt design, strength vs the standard 6.5 Grendel bolt is improved by 17%. This allows a higher operating pressure of 75,000 PSI within an AR-15 format. That, combined with the Mk3 VKO design (which recently underwent their first real life flight test), gives us a muzzle velocity of 2,770 ft/s from a 14.5" barrel with a 100gr bullet G7 BC 0.284. This approaches the ballistics of the 6.5 Creedmoor, but does so from the existing small frame format. Round weight is comparable to M855.

Additional improvements to the carrier allow for dramatically improved upper receiver life, Cam pin drag is eliminated, and operating margin greatly improved.

I'm just one guy, so chances are high this project goes nowhere, but I know it's the kind of thing that gets attention around here so I figured I'd mention it.

In new money, that's 6.48 g at 844 m/s, for 2,308 J ME with moderate recoil (but presumably a good suppressor required!).

That would appear to be light enough (in weight and recoil) to replace the 5.56 mm, while having the long-range performance to make 7.62x51 class weapons unnecessary at squad level. Sounds promising for a GPC...

PS how close can you get to that BC with an EPR-construction bullet?

For GPC I thought about a single rifle chambered for a 762 'equivalent' round,  but far more weight efficient.  Let's say 6. 5mm polymer case. 

The rifle can caliber convert to a much smaller round,  e.g.  a 204 vartarg type of round.  This means that most times you can deploy the small round.  If fighting moves to the mountains you can switch to the 6. 5

Have you tried a 120-grain bullet yet? Seems like that might be wanted for a long-range loading. But like autogun says, it looks promising. Good luck with the system!

We just got done with the FEA on a new bolt iteration (newer than the last one) which should bring the MAP up to 80,000 PSI, which is right about the limit for composite cases anyway. Performance up from 2,770 ft/s to 2,830 ft/s. We're still using Carpenter 158 lol.

autogun said:

PS how close can you get to that BC with an EPR-construction bullet?

Depending on design, identical. I have some schemes for that.

Farmplinker said:

Have you tried a 120-grain bullet yet? Seems like that might be wanted for a long-range loading. But like autogun says, it looks promising. Good luck with the system!

The 100gr bullet already has BC comparable to a 130 grain VLD. Going heavier sucks up a lot of volume in the case; I have heavier projectiles but they're not a good fit for the Grendel.

I chose the Grendel primarily for its problems with bolt web thickness and strength. Solve those (and it's looking like I have) and you can put about anything that fits in the AR-15's chute down the spout.

For reference, it's already producing over 500 J at 1,000 m.

Yeah, after I posted I realized a heavier bullet would probably take up too much powder space. Of course, when you present your system, you'll get, "We're leaning towards 6mm now".

I'm too salty for that. The system is designed to be flexible (6mm ARC, .224 Valkyrie, etc), and I have many others. Also, and this is critical, I don't expect anything of mine to go anywhere.

By the way , what are the current projectile manufacturing options being utilized other than lathe-turned as demand for lead-free ammo increases? 

I seem to remember that even in the past  prior to jacketed lead bullets, bullets like Balle D were pressure cast with high enough precision that they were still competitively used , pulled and reloaded 50+ years later