6.5CM AR Loading Questions

[Jet]

Looking for some data on loading for the 6.5 Creedmoor in ARs vs bolt guns. There is some data on the web but not a ton. Fully understand starting low and working up, watch for pressure signs, loading to magazine length, etc. With no ranges open in my area, want to preload some rounds to test when I can get back out.

- From experience, can an AR (Aero lower and upper in my case with 18" 1/8 barrel) handle similar pressures as a bolt gun? If not (like an M1A), what do you reduce your charges by?

- Have plenty of R16, H4350 and Varget plus numerous 139-142gr bullets from various manufactures and Starline SRP brass. No lighter bullets on hand at the moment.

- Any advice/recommendations would be appreciated.

Thanks and good shooting.

Rich

 

[mac86951]

Well, unfortunately there's no magic in an AR load, so let me cut to the chase.

Can an AR handle the same pressures as a bolt gun? Yes and no. Define handle pressure.

Most patterns of large format AR have the same "flaws" in respect to 6.5 Creedmoor. Those "flaws" are the bolt / firing pin clearance and the gas system. How those flaws will affect your rifle is the real question.

Ok, what does this mean? Let's start with bolt / firing pin. There's excessive clearance (room for dirt to clear out and reliable). Expect cratered and pierced primers as your pressure limit; which most likely will be less than a bolt gun due to this. JP has a bolt for you if you care to do something about it.

Second:. Gas system was designed around a 168 and 4895 burn rates. All 308 designs are a bit overgassed in 6.5 creedmoor. Overgassed means tries to eject the brass violently, or early in the interior / exterior ballistics cycle of the semi-auto. If I had a do-over; I'd order my 24" barrel with rifle length +2 or +4 on the gas tube length. (And probably a 26" barrel). FYI overgassed is case head swipe.

Hmm; ok so here is where most people stop reading and buy new parts. Why? Cause they don't keep reading.

What do you want to do with your AR? 18-1/8" barrel; I'm thinking 1300y shots were not your goal. I'm guessing you wanted something easier to handle and carry. Work up loads and look for the two problems. If overgassed is a problem before primer cratering; then load within those limits, or get an adjustable gas block and dial it down. If cratering is a problem before overgassed; JP high pressure bolt OR, be careful selecting factory ammo! Actually, if this is the case i do recommend the JP high pressure bolt and have headspace checked by reputable gunsmith (with JP bolt). I like to shoot factory ammo in my creedmoors too.


I have an off the rack DPMS 24" upper that shoots lights out (195-10x at 600 on a shfty day). My load: 139 Lapua scenar; 2.800"; CCI BR2; 40.0gr H4350. Velocity ~2650fps. I'm shooting prone off a front rest and rear bag. Nowhere near what the overpressure bolt guys are doing. Mine will overgass first and I'll lose brass to case head swipe, and R16 and slower burning powders makes it worse due to higher gas port pressures.

My thoughts and experiences to share?: h4350 will be a beast in an 18" barrel with 140 class bullets. Will it work? Sure; but I'm thinking you'll get much better burn rates, pressures, less flash, with Varget and 120 class bullets.

Test them both. Measure your velocities of loads your rifle likes; I'm guessing you'll find the 120gr class has a leg up on the 140s within 600y (when BC of 140 class really carries it). 18-1/8" barrel; your velocities at 600 are barely deer at best at 600 anyway, so see previous paragraph which I think will keep your gun running better.

Will an AR stand up to bolt gun pressures? Yes, maybe. Will the brass be reusable after? No. Certainly.
More questions?
-Mac

 

[Jet]

Thanks for the detailed answer