It’s a bad time to start this project but…

What caliber besides 308 and 6.5 creed can one be built?  I’ve got several 308 battle rifles, don’t want another one.

I have plenty of 7mm/08 brass, would that be the way to go?

What about 25 creedmoor?  Any other suggestions?

.243 is what I went with.  A 7mm-08 would be cool as well.

About 24 of these are easily available. Some of these are wildcats.:

.220 Swift
.22-250 Remington
6mm-250
.243 Winchester – same bolt as 7.62×51
6mm Remington
6mm Creedmoor. Same bolt as 7.62x51.
.257 Roberts
6.5×47mm Lapua
6.5mm Creedmoor – same bolt as 7.62×51, and can be formed from 7.62×51 brass.
.260 Remington – same bolt as 7.62×51, and can be formed from 7.62×51 brass.
6.5 WSM
.270 Winchester Short Magnum
7mm-08 Remington – same bolt as 7.62×51, and can be formed from 7.62×51 brass.
7.62×51mm NATO – Original AR-10 cartridge
7mm Winchester Short Magnum
7mm Remington Short Action Ultra Magnum
.308 Winchester – considered interchangeable with 7.62×51mm NATO according to SAAMI.
.300 Winchester Short Magnum
.300 Remington Short Action Ultra Magnum[31]
.325 Winchester Short Magnum
.338 WSM
.338 Federal – same bolt as 7.62×51, and can be formed from 7.62×51 brass
8.6 Blackout
.358 Winchester – same bolt as 7.62×51, and can be formed from 7.62×51 brass
.358 Winchester Short Magnum
.375 Raptor – same bolt as 7.62×51, and can be formed from 7.62×51 brass
.375 Winchester Short Magnum
.416 Winchester Short Magnum
.450 Marlin
.45 Raptor
.458 HAM'R[32]
.458 WSM
45-70 Auto
.458 Winchester Short Magnum
475 Bishop Short Magnum
.50 Krater
.500 Auto Max
.500 Phantom
.500 Whisper
.510 Whisper
.510 Winchester Short Magnum

From wiki

Anything that is based on or super close to a 308 is pretty easy. Anything that fits has been done at one time or another. Make sure and do your research because the further you stray from the norm the easier it is to end up with a problematic gun. 7-08 has been done a bunch so I'm sure you can find info on that pretty easily. I've never seen a 25 Creed but with 6mm Creed being more common there has got to be data between it and the 6.5.

Wow!! I didn’t know all of those are available.


Barrel length? I’d like to be able to move around, 16 to 18? 20?

If you are actually carrying it I probably wouldn’t go over 18”. AR10’s are already heavy and long. 20” and longer are great for target work but in my opinion they get unwieldy.

Quick search found Wilson makes an 18” 7-08 that looks light a lighter profile
https://shopwilsoncombat.com/BARREL-7MM-08-REMINGTON-TACTICAL-HUNTER-18-ROUND-STAINLESS-GLASS-BEAD-1-9/productinfo/TR%2D708THRG18RT9/

The other options don't get much of a mention, because in many cases the ammo isn't commercially available - or has very low availability compared to 0.308 Win and 6.5 Creedmoor.  And/or that ammo is going to have sky-high pricing.

https://www.thetruthaboutguns.com/6-5-creedmoor-vs-308-winchester/

The author of that article teases 0.308 guys pretty hard, but it's full of good info.  At the end he talks about the fact that somebody did testing with 0.206 head-to-head with 6.5 Creedmoor and the results were nearly identical, but 0.206 is apparently a British round and expensive.  So, people don't tend to chamber for it here.

The only reason I did a 0.308 build over Creedmoor is I already reload 300BLK, which uses the same pill and my silencer runs on both, so all same-same.  Purely an economic decision.

Regarding barrel length, there's an excellent video that talks about keeping barrel length in a "sweet spot" - long enough to burn the powder of the cartridge to maximize muzzle velocity and energy, but short enough to keep the weapon as rigid as possible.  The longer the barrel, the more flex you get from the shockwaves that travel the weapon.  The thicker the barrel, the more rigid the build, the fewer gyrations at the muzzle as the bullet is still traveling down it.

This guy covers heat dissipation, too, and I think he does a pretty good job of it.  It's all about the trade-offs of what you're trying to accomplish and your priorities as a shooter: https://www.youtube.com/watch?v=yAvh0PVKFRo

Accuracy Systems will build you an AR10 upper in about any caliber you want.

Accuracy Systems

Why fuck with a 450 Socom, when you can have a 450 Marlin?