Home Forums Hunting & Shooting AR and Tactical Rifles AR 10 build - barrel length and profile recommendations?

Got an AR10 buffer tube an/spring/buffer yesterday and assembled it to my lower. Next steps are to get a BCG and barrel.

The likely chambering is .308W but 6.5CM is a distant possibility. Some AR10's I've held were ungodly heavy on the front end, which leave me with questions about what barrel length and profile to get. I do plan to get a lightweight handguard and the eventual plan is to add a suppressor as well. Accuracy is an important factor.

Thought I'd ask the more experienced people here what their recommendations are for length and profile, and why.



Thanks for any suggestions.

I building myself it would be a 20 inch tube

If you are going to add a suppressor to a 308, I don't think I'd consider anything other than a 16". If not I'd go at least 18 or 20. I don't like the blast of a 16" 308, especially if it has a muzzle brake.

Profile? Sorry, I like em heavy and I like to shoot them prone. Maybe someone else will chime in.

ETA: Faxon makes some different 308 barrels - http://faxonfirearms.com/barrels/?sort=pricedesc

Everything is a compromise, it all depends on your intended use for the rifle. If its a bench gun that you don't plan on walking far with, go with a long, heavy barrel. They are easier to shoot accurately and don't heat up as fast. If its a hunting rifle, I'd keep the length at 18" or so and go no heavier than a mid weight barrel.

I started my 308 with a 20" lighter weight Lilja (.750" under the handguards and forward of gas block) with a rifle length gas system. I love the barrel profile, no complaints with weight or accuracy. A while back I cut it back to 17" to be a little more handy with a suppressor attached. I also found it runs smoother with the gas port closer to the muzzle, especially with the suppressor.

Large frame 308's are fun to shoot but they aren't mountain rifles and really don't even make a practical hunting rifle. To get them to balance right, they need a little weight out front so they are usually going to be 9-10lbs+ with a scope on them.

Thanks to all.

I'm not building a mountain rifle or even a rifle that will get carried a lot. The suppressor will be a quick detach type that will be shared with other rifles.

Already have a 16.5" Ruger Scout .308 and am leaning toward a 20" tube for this one.

Truth is, I'm not sure WHY I'm building one except that I CAN. Although I had been telling my wife Trump would win ever since he got the nomination, I bought the lower and upper before the election thinking if Hillary won the prices would skyrocket. Now that I have the parts, I can't seem to just leave them in the safe...

Guess the main goal is to have FUN. It will likely be a range gun 99% of the time. I say its not intended to be a match gun but my favorite at the range is banging steel and clays at 500 and 600 yards.

The heart of an AR-10 is the bolt carrier group, it's heavy. Next is the appropriate buffer, it's heavy too. Trying to balance it out with a light barrel won't work.

So go 20" and make it heavy enough to settle down good, it'll help negate zero shift when hanging a 1 lb. can off he end of it.

A handy dandy AR-10 carbean just doesn't work out well.

I highly recommend the Lilja barrels. Either their 20" or 18" medium weight would be an excellent choice. Both have rifle length gas systems which I would recommend for any barrel length 16"-20" on a 308.

Lilja, you say. I got a buddy that has a DPMS 16 inch barreled model. He wants to put a 20 inch barrel on it. I will pass that on. Oh and where can he get the best deal?

I bought direct from Lilja. If you send them your bolt they will check headspace for you also, if he doesn't already have he gauges.

Having owned the S&W MP-10 with a light profile barrel, I really thought it would be the way to go for a field rifle. After about a year of trying various loads, I couldn't get it under a couple inches with any of them. It shoot pretty much everything OK, but nothing really great.

The accuracy would have covered everything I want do, but the excess weight and the accuracy difference between the AR and a bolt rifle pushed me to let it go.

I would agree that the heavy barrel, while less carry-able, is probably going to be better on the firing line than a light profile one.

Ballistics Advantage makes barrels for Aero, and seem to have a good reputation for casual shooters. I'm finishing a 6.5 CM upper at the moment, like the OP, I had the parts...

First off, 308 AR's are different the AR15's. The main differences are obviously size and weight and one that's not obvious is that they are more critical to shoot accurately than bolt guns. Any flaw in technique or follow through will show up with a 308 gas gun that won't in a bolt gun. Shorter barrels tend to show less issues with bad technique than longer barrels.

Second, There is no way I would choose to shoot a 20in barreled AR10/SR25 unless it was a dedicated match rifle. A 18-20in barreled 308 AR with a suppressor is just stupid ungainly. Suppressed 308 gas guns that are not dedicate match rifles, are best with a 16in barrel... or shorter. They can still be shot to past 800 yards, yet are somewhat manageable. They're still pigs, but manageable pigs.

I have a couple of Armalites. One got rebarreled to an 18" medium weight Shilen/Rainier Ultramatch barrel in .308. It shoots well, consistently around 1"-1.25" with a variety of loads.

I also have a SASS that's never been able to do much under 1½", despite much fiddling with loads, trigger, big Nightforce scope, etc. I think I will make a 6.5 Creedmoor out of this rifle, although a really primo .308 bull barrel might shrink groups a lot as well. The rifle is heavy, and comes with adjustable gas block, so I think it will eventually get a can.
McGowan will build a Armalite pattern barrel, so will Krieger. I'll probably have Krieger do it as it's really annoying to have a really heavy rifle that isn't terribly accurate.

My Armalite shoots well. But I end up with vertically strung groups off the bench. If it weren't for the stringing, it would shoot 5 shots just around 1/2 MOA.

But Formidilosus is right, it's a pig. IMHO all 308 ARs are pigs. Huge BCGs with bolt releases you have to pound.

My "light" (10 lbs or so) AR-10

Some of the feedback here sounds like relatively old tech for 308 ARs. It doesn't have to be that way.

I've posted this before - this is my 18" 308 next to my 16" 5.56. The 308 is slightly bigger, especially in the magwell, but only weighs 1/4 lb more as pictured.

I'm using a light weight bolt carrier that is the same weight as an M16 carrier, and a carbine buffer. The lower mass parts do help make the gun less picky about shooting technique. Tuning the gas system right makes a huge difference too.

Never seen any difference in the bolt release compared to my AR15s. They feel/function the same to me.

The barrel is not a big heavy pig, or a super light profile, but it shoots well without stringing. I could carry it hunting if I wanted, the bulk is more an issue than the weight.

I will say that my buddy's 16" DPMS is considerably heavier and doesn't run nearly as well.

While I'm at it, how about recommendations for a cheap handguard?

Need DPMS high profile type. Since this will be a scoped rifle, I don't have any real need for a rail or keymod or m-lok slots. No slots at all is OK, too.

Weight is a concern so if keymod is lighter than m-lok I'll probably go that route. Seems like 15" to 17" will be the likely winner, depending on barrel length, most likely 18-20".

TIA

Are you referring to that goofy "high top" setup DPMS made? Or does it look like my pic above with a standard height rail? The pic in your OP looks like a standard rail, not a high top, but I think DPMS did make a couple variations that are similar in height. I think what you have in the OP is considered "standard height", with one of DPMS's options being lower than that. I could be wrong though, and it's hard to tell from a pic.

I don't think there are many (any?) "cheap" 308 handguard options. The one in my pic above is a 15" Midwest SS series, I'm a fan of their SSK handguards. They have newer versions now but I don't know if any of them are for a high rail.

"DPMS high" profile is pretty common and is whats needed for Aero uppers, MEGA, SR-25, and many other manufacturers. It's not the upper with the super high riser.

No, not the 'goofy "high top" setup' but rather the "high profile" that was standard on DPMS rifles until they came out with the "low profile" rail.

I've been looking at the MI guards, including this 15" M-Lok version:

https://www.midwestindustriesinc.com/product-p/mi-308ss15-dhm.htm

Have fond some keymod guards in the $147 to $165 range but prefer the M-lok. Don't know it I prefer it enough to pay a $50 premium.

Have also found some 16.5" and a 17" guard. Might consider them if I go with a 20" barrel.

Yondering -

Thanks for the details. The last few days I've been thinking an 18" barrel with an adjustable gas block is probably the best choice for me. Glad to hear it is only a few ounces heavier than your AR-15.

You mention a light weight BCG. Whose are you using?

I lighten my own carriers, but the final weight is very similar to JP's steel LMOS carriers. My 308 carriers finish out at 10.4 oz with the gas key, similar to an AR15 full auto carrier. IIRC the stock carriers were 14+ oz. I think JP's LMOS is ~10.8 oz and of course are good high quality.

I re-profiled my PSA barrel, but you can buy light 308 barrels from several companies now, Faxon is one that comes to mind. I forget the exact weight, but IIRC my 18" barrel ended up at 33 oz, and Faxon sells one that is 32 oz I think, although that may be a 16".

Definitely +1 on using an adjustable gas block. Partly because there can be a big difference in port pressure between mil 7.62 and some commercial 308; my rifle runs either one well but needs to be tuned for it, commercial 308 ends up overgassed and shoots poorly if tuned for M80 ball.

I own or have owned multiple 16", 18", and 20" large frame ARs in 308 & 260. All are run suppressed. No two ways about it, the 16" is the one I grab the most. The others aren't even close. With a can they get stupid long and the 16" is the sweet spot. I fought this for years and built 18" & 20" guns because I was concerned about velocity. Eventually I landed on the 16" just like a shooting buddy who had already been through the same experience said I would.

......175 SMK are leaving the 16" gun trial 2510fps. That's 10fps slower than the 20" barrel.

Nice, that's valuable info.

What's your load for that one, if you don't mind sharing?

LOL.

18 inch .308 with 7 inch Ti can is pretty far from "stupid ungainly".





Large frame AR-10 are ungainly but the problem is not the barrel.

Check out monstrum tactical of you aren't looking to break the bank on a 308 DPMS handgaurd. Under $100 including barrel nut

Thanks, but all I saw there was DPMS low-profiles guards.

Found this tonight:

Mentium USA
15" Slim M-Lok Free Float Handguard for High Profile .308 Rifle

Regular price $69.99.

https://www.mentium-usa.com/products/mentium-15-slim-m-lok-free-float-handguard-for-308-rifle



Slim profile and looks pretty lightweight with 2 partial Picatinny rails, both undercut.

For $70 and free shipping I don't know how I can go wrong.

You generally get what you pay for with AR parts. I'd personally pay a little more for a handguard from a quality manufacturer.

It's your money.

I don't see any anti-rotation locks, nor do I think any light weight rail without a Picatinny spine will hold up. But it's your money.

No argument about getting what you pay for, at least most of the time.

Guess I'll find out what the quality is like in a few days. The handguard adds nothing to accuracy and for now I intend to spend the money saved on the barrel. If necessary, the handguard is easy to upgrade later.

Will post my thoughts on its quality after I receive it.

I don't see any locks either. Guessing it just relies on the tightened barrel nut, which means it is adequate for now but likely to get changed out down the road.

As to the Picatinny spine, the base (to the bottom of the slots) is there, it is just missing the ridges, which add weight but nothing to strength.

Good point on the locks. For now my intent is to get the thing and running. Still need the barrel and BCG. Haven't decided on the BCG but looking hard at Ballistic Advantage for the barrel. Any experience with their stuff? (My goal is MOA accuracy, not match accuracy.)

I haven't used them but have heard good things about X-Caliber barrels. They do have an appealing "spec your own" ordering system, where you choose twist, rifling, profile, etc.

I did reprofile an X-Caliber barrel once, and the bore looked good to my eye but I didn't shoot it.

I'm a fan of the AP handguards...Not the cheapest out there, but they do utilize a steel nut and four screws to secure the HG in place. A very robust system in my opinion.

Question about the anti-rotation locks:

Has anyone here had a problem with a properly installed guard that did not have them?

Not talking about extreme use, just trips to the range.

I started with LaRue rails so I've never used any type of rail that didn't have them.

I did use Hogue tubes and never had one come loose but It wouldn't and won't really matter if it's just gonna be a hand guard with no front sight on it.

Even if it did come loose the gas tube would'nt let it come off on most types of barrel nuts. It might wobble back and forth but that's it.

I have not, and do use my ARs for more than just trips to the range.

However, I also install my handguards with Loctite, usually the green 680, between the nut and handguard. The only way the handguard will rotate at that point is if the whole barrel nut loosens, never had that happen though.

Given the zero lack of responses to the contrary, I'm guessing there haven't been many problems.

I've had handguards rotate loose but it was due to poor QC from the factory. A properly installed barrel nut shouldn't work loose.

I think most of the handguards with anit rotation tabs or designs are there as a fail safe, not necessarily to prevent common problems. I personally like the feature but wouldn't loose sleep over not having it.

DPMS LR338 Federal and I am pleased with the way it shoots and the big force it takes deer with. It has a Bushnell 4-30x50mm 6500elite with mil dot and LaRue one piece quick release mount.

Got home today to find the hand-guard waiting for me. No barrel yet but I screwed it onto the upper to see if the rail matched up. Perfect fit.

The hand-guard came with two 2-3/8" m-lok Picatinny rails, barrel nut, shims and screws. Was not expecting the rails.

The hand-guard rail is milled out on the underside to further reduce weight.

If I were to find faults it would be these:

1. The spacing on the guard's Picatinny rail does not match up perfectly with the spacing on the upper. (Don't know it that is normal or not.)

2. The edges of the cutouts on the guard are a little sharper than I would prefer. Some time in a tumbler or maybe some sand-blasting would have helped.

For $69.99 delivered, though, I am quite happy with it.

Now to get a barrel!

Who makes the rail?

I got it here:
https://www.mentium-usa.com/products/mentium-15-slim-m-lok-free-float-handguard-for-308-rifle

$69.99 delivered.


Edited to add:
Just a reminder, this is for the original DPMS high-profile rifle and compatibles.

I have tried using Mentium's products too and never got disappointed with it. They deliver fast and their products are usually as displayed in pictures. Highly recommend them!

Criterion for the barrel. I have 4 of them for ARs and all are shooters. My 308 is a 18” mid. Very happy with it. 2 16” lightweights in 223 Wylde and a 20” in 223 Wylde. Very accurate.

I've heard good things about criterion barrels. How "accurate" is your 308? To be exact... I have been thinking about turning my AR10 308 into a 6.5 creedmoor. Might think about criterion when that happens...

Faxon makes 16" 308 and 6.5 that are sub 2lbs, these things do get heavy fast, my 308 is 11lbs and my 6.5 is 13lbs, the next build will be lightweight

A thread on building an accurate lightweight 308 or 6.5 AR10 would be cool...

I'm trying to decide on this 6.5 cm or 308.. right now really leaning towards 6.5 cm. I would definitely use psa bcg it has the double plunger boltface on it which is supposed to help with reliable feeding/extraction. I was reading with the 6mm cm this is not as critical and you can use a standard bcg from a 308.. my buddy has a AR10 18inch barrel with can and it looks fine too me.

how would double plungers help with feeding? I'm assuming by plungers you mean 2 ejectors in the bolt face? All they do is put outward bound tension on one side of the rear of the case so it flies out when it clears the port?

No flame at all, just honestly curiuos. Only way to learn sometimes.

FWIW I took my 308 to AK, (bolt) and rebarreled a 243 to 6.5 cm for Carolyn while I'm gone and even when I'm back. A bit flatter and wind resistant, but all in all, I just don't feel there will be tons of difference on game actually.

Jeff

Yes two ejectors.. Apparently PSA had major issues with the gen 1 BCG's and redesigned it with two ejectors.Maybe the 1 ejector wasn't enough to eject the case? I know some will say it works fine on a 308. Hey I'm just the messenger here . Here is a pretty good video highly recommend you fast forward to the 8:40 minute mark this is where they talk about this BCG. Enjoy.

I have tried using Mentium's products too and never got disappointed with it. They deliver fast and their products are usually as displayed in pictures. Highly recommend them!