AR-10 variant reliability

[GT1975]

So, using some foresight into some possible outcomes of events, I decided to stock up on ammo in 7mm08 and 260 remington which were available for much less $ when 6.5CM prices took off but have similar enough ballistics for my purposes. I know magazine type, bolt carriers, port and tube length, buffer, receiver/chamber geometry all will come into play BUT...is there a general understanding that any of the above calibers may be problematic in terms of reliability more so than others? Let's assume they are being used in a factory upper and matched lower and have no initial feeding issues, but thinking about it in terms of typical round dimensions vs magazine/feed ramp geometry any known problems that could pop up when you need your rifle to be reliable? How about 6.5 CM vs 308 same question?

thank you!

 

[Bigtrucknut]

I don't think you can go wrong with a .308-based cartridge in the LR DPMS platform. I have LRs in the traditional .308 and in .243 Win - both function extremely well, are reliable, and consistent. Strongly suggest sticking with quality receivers/BCGs from the same manufacture if possible and thinking through and researching your build before dropping coin. I just recently picked up a spare upper and thought that I may build a 260 Rem myself. Good luck.

 

[LRRPF52]

7mm-08 is really similar to .308 as long as you are shooting the 139-154 weights.

The AR-10 operating system doesn’t really notice the difference in term of bore volume, port pressure, case volume, and how the action runs on this type of “fuel”. I’m speaking about the engineering side of calculating bore volume, port diameter, propellant mass, and how this all comes into play for running the action. AR-10 internal ballistics and mechanical engineering considerations are a totally different ballgame than 5.56x45 if you look at the mass and bore volume, recoil, BCG mass, action spring and buffer considerations, etc.

As far as magazines and cartridge feeding, the .308-based cases run reliably. I’ve seen incidental exceptions of original VLD projectiles slipping through the barrel extension lugs and hitting the breech face in the barrel instead of feeding into the chamber, but not on my .260 Rem shooting 130gr VLDs. None of your factory ammo you see on shelves will have that characteristic.

Things do start to change when you step into smaller bores like .264” and .243”.

I’ve owned 2 different .260 Remington large frame rifles built on DPMS receivers, one a factory DPMS LR-260 with a tight chamber that needed work, the other a GA Precision built large frame with Bartlein barrel that just runs like a raped ape for me. GAP extended, blended, and polished the feed ramps if I recall correctly.

The first thing I noticed with .260 Rem is that the firing pin aperture diameter invites a lot of blanking or primer flow that look like cratering, even though I’m well within published data on my hand loads. This happens on bolt guns too if they have generous firing pin apertures on the bolt, especially on Accuracy International rifles.

If I was doing a large frame right now in .260 Rem and wanted to eliminate as many headaches as possible, I would start with a LaRue Ultimate Upper with the 18” barrel .260 Rem option. You can choose 18” or 22” for .260 Rem.

Funny you mention this because I’ve seen .260 Rem on shelves locally at pretty much every store I go to for the past year. 6.5Cm pretty much disappeared immediately.

Get the LaRue kit and lower receiver and you have a complete LaRue large frame rifle that won’t look and function like a pile of garbage of franked-10 parts. I wish that option had been around when I was really into AR-10s.

 

[GT1975]

7mm-08 is really similar to .308 as long as you are shooting the 139-154 weights.

The AR-10 operating system doesn’t really notice the difference in term of bore volume, port pressure, case volume, and how the action runs on this type of “fuel”. I’m speaking about the engineering side of calculating bore volume, port diameter, propellant mass, and how this all comes into play for running the action. AR-10 internal ballistics and mechanical engineering considerations are a totally different ballgame than 5.56x45 if you look at the mass and bore volume, recoil, BCG mass, action spring and buffer considerations, etc.

As far as magazines and cartridge feeding, the .308-based cases run reliably. I’ve seen incidental exceptions of original VLD projectiles slipping through the barrel extension lugs and hitting the breech face in the barrel instead of feeding into the chamber, but not on my .260 Rem shooting 130gr VLDs. None of your factory ammo you see on shelves will have that characteristic.

Things do start to change when you step into smaller bores like .264” and .243”.

I’ve owned 2 different .260 Remington large frame rifles built on DPMS receivers, one a factory DPMS LR-260 with a tight chamber that needed work, the other a GA Precision built large frame with Bartlein barrel that just runs like a raped ape for me. GAP extended, blended, and polished the feed ramps if I recall correctly.

The first thing I noticed with .260 Rem is that the firing pin aperture diameter invites a lot of blanking or primer flow that look like cratering, even though I’m well within published data on my hand loads. This happens on bolt guns too if they have generous firing pin apertures on the bolt, especially on Accuracy International rifles.

If I was doing a large frame right now in .260 Rem and wanted to eliminate as many headaches as possible, I would start with a LaRue Ultimate Upper with the 18” barrel .260 Rem option. You can choose 18” or 22” for .260 Rem.

Funny you mention this because I’ve seen .260 Rem on shelves locally at pretty much every store I go to for the past year. 6.5Cm pretty much disappeared immediately.

Get the LaRue kit and lower receiver and you have a complete LaRue large frame rifle that won’t look and function like a pile of garbage of franked-10 parts. I wish that option had been around when I was really into AR-10s.

Thanks for the detailed reply - Do the HP bolts that have reduced apertures for 6.5 CM vs .308 take care of the .260 issue you bring up?

 

[LRRPF52]

Thanks for the detailed reply - Do the HP bolts that have reduced apertures for 6.5 CM vs .308 take care of the .260 issue you bring up?

The “High Pressure” bolts are meant to address that problem, yes.

It’s not a cartridge-specific problem, but more of a relative bullet weight for the bore problem.

Shooting 140gr and higher in .260 Rem or 6.5CM invites the primer flow problem to show up more, just as shooting 175-185gr in .308 does.

Peak chamber pressure may be the same, but the pressure curve stays higher longer due to the resistance from the heavier projectile. It puts more strain on the primer with slower-burning powders vs lighter bullets getting punted out with faster powder.

It’s one of the main reasons why I only load 130gr or lighter in .260 Rem gas guns.

 

[Vivacious Stallion]

As long as you go with a quality brand most of the ar10 gun's I've had experience are pretty reliable. I haven't noticed many feeding issues with the 6.5 cr ar10s I've used or that my friends have. However, lots of ar10s are pretty over gassed. My lmt mws in 308 was pretty gassy with a can before I changed to an extra heavy buffer (of course they are known for this and xtreme mil spec reliability or whatever). But my dad has an aero precision that is incredibly brutal but he seems to not mind. I think something might be wrong with that gun and that it's not representative of aeros ar10 lineup.

Are you looking at buying a complete rifle or building a rifle?

 

[GT1975]

As long as you go with a quality brand most of the ar10 gun's I've had experience are pretty reliable. I haven't noticed many feeding issues with the 6.5 cr ar10s I've used or that my friends have. However, lots of ar10s are pretty over gassed. My lmt mws in 308 was pretty gassy with a can before I changed to an extra heavy buffer (of course they are known for this and xtreme mil spec reliability or whatever). But my dad has an aero precision that is incredibly brutal but he seems to not mind. I think something might be wrong with that gun and that it's not representative of aeros ar10 lineup.

Are you looking at buying a complete rifle or building a rifle?

I have most of the parts to build them including matched receiver sets from wilson, ADM, mega, aero, RCA BCGs, just missing a .260 barrel waiting for the right deal, but it's tempting to just do it all via LMT MWS barrel swaps too except I'm not paying $1000+ for the 6.5 barrel. Hell I'll probably end up doing both who am i kidding, will just slowly piece the MWS stuff together, have the 7-08 barrel already. Just moved from NJ to a free state so I had held back on all my builds to wait until now that I can do stuff without restriction

 

[larryh128]

I have most of the parts to build them including matched receiver sets from wilson, ADM, mega, aero, RCA BCGs, just missing a .260 barrel waiting for the right deal, but it's tempting to just do it all via LMT MWS barrel swaps too except I'm not paying $1000+ for the 6.5 barrel. Hell I'll probably end up doing both who am i kidding, will just slowly piece the MWS stuff together, have the 7-08 barrel already. Just moved from NJ to a free state so I had held back on all my builds to wait until now that I can do stuff without restriction

I've done several AR-10's. My initial feeling is that if you are shooting factory ammo, you're pretty much good to go, I've never had a feeding issue with a 308 body style round. Where the tuning comes in for me is when you're handloading for a specific velo. I strongly suggest an adjustable gas block and seriously I wouldn't put together an ar-10 without one. A can on the end also requires an adjustable gas block. I like flat wire buffer springs and heavier buffers as well. With that said, I've never had a 308 that wouldn't run stock with factory ammo.

 

[Vivacious Stallion]

I have most of the parts to build them including matched receiver sets from wilson, ADM, mega, aero, RCA BCGs, just missing a .260 barrel waiting for the right deal, but it's tempting to just do it all via LMT MWS barrel swaps too except I'm not paying $1000+ for the 6.5 barrel. Hell I'll probably end up doing both who am i kidding, will just slowly piece the MWS stuff together, have the 7-08 barrel already. Just moved from NJ to a free state so I had held back on all my builds to wait until now that I can do stuff without restriction

I like my MWS a lot but now is not a good time to buy them or the parts. I know some places make after market barrels or fit other manufacturers barrels to them but idk the cost of this path. The qd barrel system is pretty much the sh*t. I went with the lmt because I wanted a really solid reliable gun (after owning a DT mdrx ) that I didn't have the potential to f*ck up myself and my friend wanted to let his go for a decent deal.

I'd agree with Larry above, put a good adjustable gas block on it. I know the seekins throw lever block is pretty cool on a sp10m I shot. Then you're set if you use a silencer.

Sounds like you're on the right path though. Make sure and post pics once you start slapping them together!

 

[GT1975]

I like my MWS a lot but now is not a good time to buy them or the parts. I know some places make after market barrels or fit other manufacturers barrels to them but idk the cost of this path. The qd barrel system is pretty much the sh*t. I went with the lmt because I wanted a really solid reliable gun (after owning a DT mdrx ) that I didn't have the potential to f*ck up myself and my friend wanted to let his go for a decent deal.

I'd agree with Larry above, put a good adjustable gas block on it. I know the seekins throw lever block is pretty cool on a sp10m I shot. Then you're set if you use a silencer.

Sounds like you're on the right path though. Make sure and post pics once you start slapping them together!

funny thing is, spend long enough accumulating parts and in the meantime pieced together this OG P308 that I like better than the 308s I was going to build. well, still have the other calibers to build once I secure this receiver extension

 

[Kocher]

2nd the adjustable gas block..
And a small firing pin bolt head ... guys call them “ HP bolt”. “ High Pressure Bolt”
I see the same issue in 2 of my bolt guns. The primer likes to flow into the firing pin hole because it’s so overbored..Doesn’t blow any primer so I don’t care.
This can happen even in 308 like the other guy said can blow primers if you use the large firing pin bolt head, but it was more prevalent in the 6.5 Creedmoor. Most of the time the 308’s just run just fine with the normal bolt head .I almost want to go build one just because it’s so easy but I just don’t have a use for it. I do primarily varmint.
If I could do 22-250 in AR 10 I would, I don’t think it would feed well and to top it off nobody makes barrels for it after shelf and not gonna pay 800 for a barrel.

My 6.5 cm has no issues running wot, or semi! Aeroprecision BCG‘s are both small firing pin aka-high-pressure bolt. the nickel coated bcg is not.

Working with interest to see how your build turns out with the different chambers.
Finished a 22creedmoor ar10 and doing some dreaded case work from 6mm cm to get them 22CM, as your statement clearly tells the issue. No cases, or many bullets to match up with the popular calibers. Hit and miss as you say.... although I did see more 22 caliber bullets and a lot of the websites lately and quite a few 6 mm not an abundance but better than usual.

but if you don’t get the powder what’s the use.. let alone the primers

 

[Kocher]

funny thing is, spend long enough accumulating parts and in the meantime pieced together this OG P308 that I like better than the 308s I was going to build. well, still have the other calibers to build once I secure this receiver extension

View attachment 7614465

Nice..