.308 AR isn't accurate enough. Barrel swap?

[StevieP]

I build my .308 AR off one of the 80% lower group buys a couple years ago.

DPMS lpk w/ Geissele SSA trigger. Nikon M-308 scope. DPMS SASS 18.5" barrel is, I think, the problem. At 100 yards, it's all I can do to get 3" groups. I've tried many different types of factory ammo, including 'match grade' stuff, but it's still all over the place. This thing SHOULD be a sub-MOA gun, and it pisses me off that it's not.

I'm thinking of changing the barrel for something different/better. Before I do, should I try changing out my muzzle device to just a threaded protector with target crown?

Suggestions on REALLY accurate .308 AR barrels that won't break the bank?

 

[one-eyed Jack]

Have you had anyone else shoot the gun? Jack.

 

[Ben Diss]

How's your barrel nut torque?

 

[Rate_of_Twist]

What bullet weights? What's the rate of twist on your barrel?

 

[icyclefar]

How's your barrel nut torque?

Type of hand guard? Free float?

Have you tried another optic?

 

[Mountain]

Is the optic possibly moving on the rail?

Headspace checked?

 

[hminsky]

I would definitely look again for anything 'loose', considering you built it yourself

Any play in the optics mounts (or maybe internal to the scope itself) will certainly cause trouble.

 

[Rockrivr1]

What bullet weights? What's the rate of twist on your barrel?

Was thinking this as well. Wrong bullet size for twist rate.

 

[jasons]

Suggestions on REALLY accurate .308 AR barrels that won't break the bank?

Fulton Armory sells 20" stainless Criterion barrels (button rifled) for the AR-10 style rifles for $330ish. It won't last as long as a cut rifled barrel like a Krieger but they're also not $600+ bucks.

I also have a DPMS barreled LR308 and I'm unimpressed with it as well. It's not as bad as you describe but it's not as tight as I'd like it, and certainly not "sub-MOA." DPMS barrels seem to range from "OK" to mediocre at best. (Now someone's going to jump in and tell us how their 16" DPMS shoots 1/4 MOA with 50,000 rounds on it.)

 

[7.62x39]

Fulton Armory sells 20" stainless Criterion barrels (button rifled) for the AR-10 style rifles for $330ish. It won't last as long as a cut rifled barrel like a Krieger but they're also not $600+ bucks.

I am a huge fan of Criterion barrels. I have several of them, However, none of them are in 308. But I would hazard a guess that they are just as good as the wylde chambered ones that I use.

Brownells sells the Criterion chrome lined 308 barrels for $321 and the stainless for $303

 

[jasons]

Brownells sells the Criterion chrome lined 308 barrels for $321 and the stainless for $303

I'd personally go with the stainless over chrome lined if it's for an "accuracy build," and for an extra $30 I'd probably get one chambered by Fulton. The Brownells ones are probably good, I just don't know who chambers them and Fulton is pretty well respected so I'd lean in their direction.

My understanding is that Criterion's stainless blanks are made by Krieger but they're button rifled instead of cut rifled to lower the manufacturing cost. They should be comparable to a Wilson or any of the other button-rifled stainless barrels out there (which is to say very good for the price,) assuming they're chambered by someone who knows what they're doing.

 

[StevieP]

Thanks guys.

1:10 twist 18" heavy barrel. Fluted.

http://www.brownells.com/rifle-part...rel-prod54489.aspx?avs|Contour_1=Fluted|Heavy

Currently has a Griffin flash/comp on it. Thinking about just a threaded end cap as a test.

I've tried every ammo from 147, 149 up to 168, and even 180 (Core Lokt) just to try everything.

Optic and mount are rock solid. Could be the forend, but I don't think so. It is a Troy free float tube that seems secure, but I'll tighten it.

I don't have a torque wrench. Bought the AR tool from the guy on here selling his homemade ones, and it seems tight as Hell. The gas tube seems to be in the same place wrt the barrel nut, so it doesn't seem to have slipped.

I'll have someone else shoot it with quality ammo, and if it still gives such crappy groups I'll consider a different barrel.

Thanks again for the suggestions.

 

[ephemeratta]

Barrel nut, comp timing, bolt head, head space, hand guard, bore ream...
There's a lot to check before that barrel goes. Good luck bud.

 

[mac1911]

With the intention of building a 308 AR I need to ask some questions.
1. What makes you believe your set up is supposed or is capable of sub moa groups.
2. What match ammo did you try specifically.
3. Did you try all these different loads in one sitting? I learned the hard way tossing 10 rounds of this and that down the pipe in one sitting does not help with accuracy. My latest build showed this 10 fold. When I later cleaned the barrel again and just tested one load accuracy was much better...down to about 1" I still think my scope and trigger are keeping me from getting under 1" consistently.
4. As mentioned get a known good shot to test it out. I have a go to guy at my club . Ret. Marine armor . He's a very good shot and has some outstanding rifles.
He has time and time again shown me it's not the gun.

Good luck and keep us posted

 

[wmass]

I'd check the headspace and barrel nut torque. I am a fan a Rainier barrels. I've set up 2 18" 5.56 rigs with them and had great results. I plan on using them for my 7.62 build. It seems Dpms barrels can be hit or miss.

 

[Bonesinium]

Operator error.

 

[xtry51]

Have you had anyone else shoot the gun? Jack.

This.

The first thing to do is definitely find someone you know is really good shoot it benched with a known quality ammo like a box of Black Hills 168gr Match.

Before they do that make sure the barrel nut and the scope mount are tight.

 

[55_grain]

This.

The first thing to do is definitely find someone you know is really good shoot it benched with a known quality ammo like a box of Black Hills 168gr Match.

Before they do that make sure the barrel nut and the scope mount are tight.

Again, this. Get known good ammo, BH match or Fed GMM or a proven handload and a 2nd shooter, benched with 2 sandbags. I bet it's way better than 3 MOA.

How good is the glass? I've wasted lots of time trying to dial in cheap scopes that didn't hold zero. Use a known good scope.

55_grain

PS: your location is awesome!

 

[dcmdon]

I would do the following.

1) Retorque the barrel nut - not too tight
2) get some Federal Gold Medal Match
3) Confirm the scope is tight in its rings and the rings tight on the rail.
4) give the bbl a good scrubbing
5) shoot some foulers
6) give the gun to a known "good shot".

If its good then try shooting the gun yourself.

If its still bad then you have a problem.

I've found Federal GMM to shoot well in every .308 I've ever put it in. Its magical. Especially the 168s.

 

[StevieP]

I found the barrel nut *did* work itself a bit loose.

Follow-up and range report to follow.

 

[drgrant]

This.

The first thing to do is definitely find someone you know is really good shoot it benched with a known quality ammo like a box of Black Hills 168gr Match.

Before they do that make sure the barrel nut and the scope mount are tight.

All of this, so much... this this this....

-Mike

 

[StevieP]

Shit. I think I've done some damage here if the tube & key were slightly misaligned.

Definitely going to replace the tube. Do I need a whole new bcg, or can I live with the key like this, or have a 'smith replace it?

Gas key on the bcg.

Gas tube.

 

[jasons]

I'd try cleaning both up with a file before I spent money swapping them out. What do you have to lose?

 

[mac1911]

would that damage hurt accuracy?
was the barrel loose?

 

[StevieP]

would that damage hurt accuracy?
was the barrel loose?

The barrel WAS loose.

I'd try cleaning both up with a file before I spent money swapping them out. What do you have to lose?

I think the gas key can be smoothed out with a small file. The tube's cheap enough not to take a chance on.

 

[bman940]

Just to chime in on the DPMS LR-308. I had one and it was a tack driver by almost anyone's standards. Granted I bought mine 5 years ago and it easily had 2000 rounds through it and still shot .75 MOA. I could not have been happier with it in the filed either as it accounted for easily over a dozen deer. Only thing I didn't like about it was the weight! A young guy I know wanted to buy mine after borrowing it and I gave him a good deal. I'm not sure if anything about their barrel's have changed since moving all their operation's South, I just know I was very pleased. My LMT .308 and CMMG are both 1.125 MOA for the most part with hunting ammo.

 

[ephemeratta]

The barrel WAS loose.


I think the gas key can be smoothed out with a small file. The tube's cheap enough not to take a chance on.

Good call. The one part on a rifle I never try to repair is a gas tube.

 

[7.62x39]

Definitely going to replace the tube. Do I need a whole new bcg, or can I live with the key like this, or have a 'smith replace it?

Definitely don't need a whole new BCG. You don't need a smith either. The gas key is simple enough to swap out and re-stake

 

[icyclefar]

The barrel WAS loose.


I think the gas key can be smoothed out with a small file. The tube's cheap enough not to take a chance on.

Did you properly torque it the first time?

Proper procedure would call for degreasing the parts, applying Mil spec anti seize, and torquing to XX ft lbs (whatever the manufacturer calls for)

I've never had one come loose when I followed procedure.

 

[71montess]

Yes on the BCG's a small rattail file(chainsaw) would clean that up, if you need a new key, Brownells sells a key staking tool for about $70.00.