Need advice on AR-308 build...

[Jm32526]

I recently purchased a Mega Maten matched upper and lower (stripped) for a .308 build. I am seriously considering chambering it in 7mm-08. Does anyone have any suggestions or advice they can offer?

 

[AR Shooter]

What's the intended purpose of your AR-10? Targets? Hunting?

 

[Jm32526]

Intended purpose.... At this point I would probably say more target stuff then hunting, however it is my intent to hunt with it a little here and there. Originally I was going to build just a "standard" .308 with a 16" barrel and call it good. Of course I want to complicate it a little more because I got into reloading a couple years ago and I am a big fan of 7mm bullets. I was thinking I would like to use either Berger VLD's in 140 or 168 grain. In the end I just want to do something other then .308 so I am trying to gather as much info as I can to build it right the first time. About a year ago I was in the process of building a REM 700 chambered in .260 and I solicited input from members of this website. Long story short I received a ton of great info and I had a great gun built and the loads that were recommended to me were awesome also!! I was very thankful I didn't have to play the "let's build it three times and hope for the best".

 

[PRECISIONWELDING01]

Great platform to build off of.i just got done building a 26" barreled 308 match /tactical gun.went with 308 just because they are so easy to get to shoot . Mega isn't main stream but soon will be

 

[Outrider27]

A lot depends on what you want to spend - my AR-10 has only one major part that could be considered OEM - the bare DPMS lower reciever. Every thing else came from the upgrade aftermarket area (examples: 26 1/2" heavy barrel from a Kreiger blank, Geiselle 2 stage match trigger, extended (into the trigger guard) bolt release, etc.) or was fabricated by the gunsmith (items such as the recoil buffer tube, which was fabbed to accomodate the adjustable buttstock he makes, adjustable for length of pull, offset, cant, height of cheekpiece, height of buttplate), upper receiver and bolt modified to accomodate a bolt handle rather than using the stock rear mounted charging handle - you get the idea). This sort of wretched excess doesn't come cheap, but the more of it you have, the more unique and (in some respects) capable your rifle will be. Frankly, you can buy a pretty decent used car for the price of this lovely beast.

Which reminds me, I have to put it on a scale and weigh it - with that barrel, it is a bit porkey. :

Doing something like this (maybe without some of the custom touches, lol) in 7mm 08 would seem to be a really interesting and worthwhile project, and the accuracy of the cartridge is well proven - just watch how far you want to go, as the more interesting extra touches can add up to lots of $$. Plan carefully, have fun, and remember that a quality aftermarket trigger is a good place to start.

 

[markr]

The heavier bullets in 7mm may prove to be too long for practical use considering mag length.

 

[jonbearman]

Depending how the throat freebore,mag length wont make any difference in my opinion.Great pick of a cartridge that wont give you any feeding head ache's.The 7-08 is very versatile and fun to shoot.Good luck with your project.Make sure you buy a good quality blank.

 

[Raptor]

Lot of 260s floating around out there too. Makes a great round for the AR-10s.

 

[XTR]

Really depends on whether or not your application would benefit from availability of ammo. In most times there is tons 308 around in various forms, mil surp, black hills, and other manufacturers etc.., with a 7-08 you're going to have to roll your own.

Personally I love my 7-08 bolt gun, but I'm not certain I'd get it in a gas gun unless I had an eye to competitions, and in that case I'd look at both the 7-08 and the 260 for recoil reduction and improved ballistics.

 

[mac86951]

The heavier bullets in 7mm may prove to be too long for practical use considering mag length.

I'll also quote the post about the 260 as well.

AR-10 isn't as easy to change calibers as the AR-15. Gas port pressures get to be tricky (believe me, I know my AR-10 is 7mmSAUM. It took a +4 gas tube to even get close to "normal" port pressures).

7mm-08 and 260 perform very close to .308 for gas port pressures and many shooters have had good results. Go with good parts! The high BC bullets won't fit mag-length, and you might need to check the throat length too, so be prepared to single load if you want the high BC bullets, or take the time to work up good mag-length loads.

Not all -08 children run well in an AR-10. .243 is one that I've heard a good % more shooters have trouble keeping running well. Bullet weight, gas-tube length, and powder burn rate for the range of .243 mean an adjustable gas block will allow some of it to work well, and others not so much (compared to a bolt). Again, lots of time spend to develop a good hand-load. (please correct me if someone has a .243 AR-10 that has worked well).


If you want an AR-10 that runs without problems, stick to the cartridge it was designed for and keep it a .308. Wide bullet selection, and recoil isn't an issue with a Hydrolic buffer and/or muzzle break. My 7mmSAUM has ~ same recoil as .223 with both. Just be sure to double up on ear protection when using a break

Finally, Check manufacturer closely. DPMS and others might not be interchangeable, and most parts do NOT work with an Armalite, so do your research on vendors.

-Mac

 

[Jm32526]

Thank you all for the input! This is exactly the conversation I need to have. I am about 99% sure that I will be putting a Krieger barrel in the 24" to 26" range. It will definitely have a two stage trigger. I was thinking of a JP enterprises bolt (anybody got another suggestion for a bolt carrier group). I am concerned about the loads... When I built my .260 I wasn't to worried about feeding problems because it is built on a long action. Am I going to need to stick with the shorter bullets to avoid feeding issues. I was leaning more towards the 168 grain bergers if possible. Any advice on that would be appreciated. I am also concerned about the difference in parts between the AR .308 variants but I am muddling through it more or less.

 

[XTR]

I was leaning more towards the 168 grain bergers if possible. Any advice on that would be appreciated. I am also concerned about the difference in parts between the AR .308 variants but I am muddling through it more or less.

I have not tried to load the 168 VLD in my 7-08, but the 162A max I loaded over 3" long to get the tail out of the bullet. I don't think you will be able to run the Berger in a mag length load.

I would venture a guess that you will be running 140 class bullets to make bullets that will work at mag length and not interfere with capacity. I put an H-S DBM on my bolt gun (like the short 4 round mags for hunting) and I run mag length 140s at ~3000 FPS from a 24" barrel.

 

[PRECISIONWELDING01]

The bolt carrier group I used was a chrome DPMS bolt carrier and bolt .barrel extension and hand guard barrel nut was also DPMS.trigger is a geissele match trigger will not find a better two stage trigger.Bartlein barrel with two extended gas tube from arx Robert Whitley .

 

[slm9s]

Definitely 7-08 or 260 instead of 308. You'll get better ballistics AND less recoil. Surprisingly, my stock DPMS/CMMG 260 is easily under moa with 123 amaxs. Its my tactical comp gun.

 

[flatlander]

I built myself an AR10 in 7-08 using J-D Machine upper/lower receivers (DPMS style), Krieger bbl, Daniel Defense AR10 Lite 12 rail handguard, RRA NM 2-stage trigger, & LMT SopMod buttstock.

I found the Krieger blank in their online inventory list, already contoured & threaded for the bbl extension. Only downside - it's a 1-10tw instead of 1-9. I finished it at 25", left the gas system at std rifle length, and chambered it for an improved version of the 7mm-08, which has less body taper and a 30* shoulder that's blown forward .068". We went with an intermediate amount of reduction in body taper - not quite as much as a full Ackley Improved reamer - in order to make extraction in a gas gun reliable, and I've not had any issues with sticky extraction.

I drilled the gas port with a cobalt 1/16" drill, then enlarged the port with a #49 drill, then test-fired, enlarging the port as needed to get bolt lock-back on an empty magazine. Was conservative in doing this, and wound up enlarging the port a couple more times after I'd thought it was large enough. Finally wound up using a #45 drill, after several intermediate sizes & testing.

I've yet to find an acceptably accurate load with S168MKs, and wonder if that's not the result of using the 1-10tw bbl. But going to 150MKs didn't help, and I went as light as S130MKs to get good accuracy in this rig. I've had several other projects going since completing this rifle, and since I was a little disappointed with accuracy & velocity, kinda put it on the 'back burner' where load development is concerned. I was starting to get some improved results using Alliant PP2000MR with the heavier bullets, but since the hoarding shortages, hadn't been able to find more of this powder, and was reluctant to use my limited supply in this rifle, since it's my best go-to powder for 90s in the 223 & 223 AI.

Still think a 7mm-08 or 7-08 AR 30 (Kiff's designation of my reamer) was an excellent choice for the AR10 chassis, but if I knew then what I know now, I'd have ordered a 1-9 blank from Krieger instead of giving into the temptation to try to make the 1-10 blank work.