AR308 accuracy, little help needed.

[rfk25]

My AR308 DPMS was not built be me when I received it several years ago. First impressions was it is POS, it wouldn't cycle and I was lucky to have 3" MOA.
Fast forward to 2023. With three different brands of 175gr match ammo, this thing shoots approx 4" MOA. With and without the can. What gives? I'm not new to firearms and understand the fundamentals. Open to any and all ideas, roast away. TIA.

• Cycling issue has been resolved.
• CMMG lower with unknown trigger, but breaks nicely.
• Sterling Arsenal upper.
• PRS stock.
• Replaced the 18" medium BA barrel with a 20" heavy JP match barrel with bolt.
• JP rifle gas tube, and JP adjustable gas block.
• AAC 762SD suppressor mounted.
• Optic base and rings are tight.
• Bipod is tight and shooting off a rear bag.

 

[bfoosh006]

My AR308 DPMS was not built be me when I received it several years ago. First impressions was it is POS, it wouldn't cycle and I was lucky to have 3" MOA.
Fast forward to 2023. With three different brands of 175gr match ammo, this thing shoots approx 4" MOA. With and without the can. What gives? I'm not new to firearms and understand the fundamentals. Open to any and all ideas, roast away. TIA.

• Cycling issue has been resolved.
• CMMG lower with unknown trigger, but breaks nicely.
• Sterling Arsenal upper.
• PRS stock.
• Replaced the 18" medium BA barrel with a 20" heavy JP match barrel with bolt.
• JP rifle gas tube, and JP adjustable gas block.
• AAC 762SD suppressor mounted.
• Optic base and rings are tight.
• Bipod is tight and shooting off a rear bag.

I could very well be your barrel doesn't like the ammo you have tried.
I have had very good results with 168gr FGMM, and Hornady 155gr Amer. Gunner.

And, no offense, but how much trigger time do you have behind a LFAR, they do need a different bench technique compared to bolt guns and AR15's.

 

[rfk25]

I have not tried 168s yet. No offense here, lots of trigger time professionally behind M4s. I've never shot off a bench since its not real life. I'm shooting prone on nice ground with the bag and bipod. Not looking for sub-moa, but I expected 1-1.5".

 

[Hobo Hilton]

If possible, swap the entire upper. Borrow one from a friend or from some other source.
You are down to process of elimination.

 

[BCP]

Get a lead sled and a target scope. Single feed match ammo into the chamber and take your time. Then shoot fed from a loaded magazine.

I thought my 716i was basket case but in a lead sled with match ammo and a 16x weaver target scope it puts 5rds into 3/4 or better.

Out of the led sled, with a 4x scope that has a thick reticule, shooting FMJ ammo, more like 3".

 

[rfk25]

If possible, swap the entire upper. Borrow one from a friend or from some other source.
You are down to process of elimination.

Get a lead sled and a target scope. Single feed match ammo into the chamber and take your time. Then shoot fed from a loaded magazine.

I thought my 716i was basket case but in a lead sled with match ammo and a 16x weaver target scope it puts 5rds into 3/4 or better.

Out of the led sled, with a 4x scope that has a thick reticule, shooting FMJ ammo, more like 3".

Optic is a NightForce NXS 3.5-15, but the sled and single round is a good idea.

 

[Lug Nut]

I have not tried 168s yet. No offense here, lots of trigger time professionally behind M4s. I've never shot off a bench since its not real life. I'm shooting prone on nice ground with the bag and bipod. Not looking for sub-moa, but I expected 1-1.5".

Then we need to ask:

Do you shoot off the bench or prone at 1 MOA or better with other rifles?

 

[rfk25]

Then we need to ask:

Do you shoot off the bench or prone at 1 MOA or better with other rifles?

I pretty much have zero bench experience. Done it a few times and was so uncomfortable because I wasn’t trained that way. I went back to prone. I have shot 1 MOA or slightly better with issued weapons. What is the advantage on the bench over prone? I feel like for me I can get behind the weapon on the ground. More contact equals more stability right?

 

[Lug Nut]

I pretty much have zero bench experience. Done it a few times and was so uncomfortable because I wasn’t trained that way. I went back to prone. I have shot 1 MOA or slightly better with issued weapons. What is the advantage on the bench over prone? I feel like for me I can get behind the weapon on the ground. More contact equals more stability right?

I’m no expert.

Yes, prone is good and more contact can mean more stability, provided you are not using muscle to hold position.

Since you can shoot 1 MOA or better, then you know that consistency is key.

If shooting prone, using a bipod, make sure to load the bipod consistently. Be relaxed and comfortable in your position. Don’t use muscle to hold position. One can fatigue using muscle and this hurts precision.

I like shooting prone, but I shoot better from the bench. It’s easier for me to be consistent and comfortable, especially when shooting for extended periods of time.

If shooting prone for extended periods, I fatigue, lose form, and generally suck. This becomes glaringly evident during multi day events, when I go prone on day two. I’m sore before the first round is fired.

Now, I know that one should not fatigue using proper form while shooting prone. I’m just not there, yet.

It looks like you now have a good barrel. I would guess you should be able to do 1 MOA or better with that set up.

My Fulton DPMS .308 shoots consistent sub MOA, and I’m no rifleman.

You may find it easier to be consistent from the bench.

And since one can’t drag a bench everywhere, prone is a valuable skill, for sure.

 

[BCP]

Shooting it with a different optic and no muzzle device is another test.

The lead sled is a real life saver for troubleshooting accuracy issues and sighting in rifles since it will hold the rifle in place.

 

[rfk25]

I’m going to give the bench another try. Good ideas.

 

[LRRPF52]

The JP barrel should be shooting 1 MOA or better for you.

How sloppy was the barrel in the upper before you tightened down the barrel nut?

I’ve had Kriegers and JPs that didn’t shoot until I bedded them into the uppers. They were shooting 1.7” groups before I re-built them with an accuracy checklist.

Once I bedded them, the .308 billet receiver set Krieger combo shot 5rds in the .6s consistently with an existing load not even tuned to that rifle, and the .223 Wylde JP shot .3" - .5” groups.

 

[gopherslayer]

Was going to ask if it was bedded but lrrpf beat me to it. I have a PSA AR 15 upper that’s loosey goosey and will be bedding it.

 

[Expert684]

Try this: make sure EVERYTHING is tight. Scope, mount you name it.
Shoot 3 rounds of FGMM 168 or 175. Just for group size. Shut the gas system off load 1 round at a time of FGMM. Open the gas block just enough the gun cycles an locks open. Then shoot three more rounds for group size and see if the group size changes?
I did this with my DPMS 308” 18” barrel gun. It shoots .375” all day. 5 or ten shots. Mine was over gassed.
Just a suggestion.

 

[LRRPF52]

Even with free-recoiling the rifle, it should be shooting in the 2” region with those loads.

Something is loose, not aligned or square, or scope issues.

Gas guns in larger calibers require very attentive gas gun fundamentals.

You can lazily get away with loose fundamentals on a .223 Rem, but not a .308 Win.

 

[rfk25]

I've got a few things to test out one at a time.

• Recheck torque specs
• Close off the gas port, take gas out of the equation
• Remove the AAC762
• Find a lead sled
• Keep playing with loads

I've seen a few mention lapping the upper, are tolerances on uppers off enough that this a real problem? Is this something that everyone does even on new builds just because its a known issue?

Seems like gas with AR308s is much more of a thing than AR15s. I'm used to finding the spot in the gas block that locks the bolt back and then turn it 1/2 more to account for "just to make sure" scenarios. Maybe I've got the gas port open too far? Brass is landing around 4:30. Guns that run dirty (to a point) don't bother me. They get cleaned, but I always wanted mine to have the power from the gas to cycle no matter what.

 

[Billiam1211]

So a lot of the stuff mentioned here will certainly help improve accuracy HOWEVER I’m not sure any these solutions will turn a 4 inch group to a 1-1.5 group. Try and have another buddy shoot it too, my friend got on my AR10 and stacked a tiny group at 600 which made me feel like shit

I struggled with my AR10 a bunch and eventually came to the conclusion that it was me. My other rifles all shoot 1/2 MOA and sometimes better… AR10 in 308, crushed my ego. I spent a TON of money troubleshooting parts and it helped but in the end I had to learn how to show my AR10 and it’s slightly different from my other rifles.

currently running an Aero m5 upper, Wilson Combat 20” barrel, Rubber City BCG, SLR agb, and SCS buffer set to H2. When I’m on point, I can stack shots in sub minute groups HOWEVER when I’m tweaking my NPA and getting settled it sends shots all over the place. I think you’ll have better luck taking good ammo and play with your NPA, rifle to shoulder connection, grip, and follow through. Once it starts shooting remember what you did and try to replicate it.

 

[rfk25]

So a lot of the stuff mentioned here will certainly help improve accuracy HOWEVER I’m not sure any these solutions will turn a 4 inch group to a 1-1.5 group. Try and have another buddy shoot it too, my friend got on my AR10 and stacked a tiny group at 600 which made me feel like shit

I struggled with my AR10 a bunch and eventually came to the conclusion that it was me. My other rifles all shoot 1/2 MOA and sometimes better… AR10 in 308, crushed my ego. I spent a TON of money troubleshooting parts and it helped but in the end I had to learn how to show my AR10 and it’s slightly different from my other rifles.

currently running an Aero m5 upper, Wilson Combat 20” barrel, Rubber City BCG, SLR agb, and SCS buffer set to H2. When I’m on point, I can stack shots in sub minute groups HOWEVER when I’m tweaking my NPA and getting settled it sends shots all over the place. I think you’ll have better luck taking good ammo and play with your NPA, rifle to shoulder connection, grip, and follow through. Once it starts shooting remember what you did and try to replicate it.

I totally agree, I got my soul crushed since I thought I was a decent shooter. Thankfully, I had a former trigger puller shoot it and he couldn't do any better. I'm not giving up, but its been humbling. I would like to receive formal long range instruction once its dialed in.

 

[bfoosh006]

I've got a few things to test out one at a time.

• Recheck torque specs
• Close off the gas port, take gas out of the equation
• Remove the AAC762
• Find a lead sled
• Keep playing with loads

I've seen a few mention lapping the upper, are tolerances on uppers off enough that this a real problem? Is this something that everyone does even on new builds just because its a known issue?

Seems like gas with AR308s is much more of a thing than AR15s. I'm used to finding the spot in the gas block that locks the bolt back and then turn it 1/2 more to account for "just to make sure" scenarios. Maybe I've got the gas port open too far? Brass is landing around 4:30. Guns that run dirty (to a point) don't bother me. They get cleaned, but I always wanted mine to have the power from the gas to cycle no matter what.

Lapping has helped quite a few of my LFAR's , and when assm. them I just do it because it is so easy. I also Loctite the barrels RE into the upper.
Did the TnG ( true and glue ) make every factory load better ? No, but the ones that did improve, made me a believer.
Thread link and not a beat all test, but good enough for me.... https://www.ar15.com/forums/industr...-again-UPDATED-with-Tn-G-results-/301-285762/


You mention the gas differences between a AR15 and a LFAR ( large frame AR ), and while that is some of its differences, the added mass banging around can be just enough to skew your results. That is why I mentioned it earlier.
That mass will cause accuracy issues if not given full attention.

I typically prefer to shoot off a bench, for precision shooting... I don't like "sleds".. I use a front bag and a squeeze bag for the rear.
I tend to allow the LFAR to quit bucking well after the bullet has left the barrel.
To me it helps keep the firearm in the same repeatable GTG position for the next shot.

You might consider trying one of these https://www.midwayusa.com/product/1015049090?pid=610698
When used properly, they help quite a bit.
Place the forearm into the "V" then spread the bottom "v" outside legs... doing that will "clamp" the upper V around the forearm.

Gas block wise... do the single round , mag fed loaded round test.
One round mag fed and loaded, fire, making sure the BCG locks back.
Add one click open, for good measure. I don't know how the JP Adj. GB works ( clicks or threaded screw ).. but for reference my SLR's have 15 usable clicks... I have mine set for 6 clicks open from closed. My brass tends to fall at about 4:30 as well.

Also, make sure your gas tube interacts with the gas key smoothly... no binding, or clunky interaction... Any clunkiness will transmit down to the gas block and barrel and make for poor groups.
FWIW, I have few LFAR's that just don't like the 175gr loads.

How many rounds through the JP barrel ? It is possible it just wants a little more break in.

 

[rfk25]

I'll grab one of those bags for and give it a go. I'm guess the barrel has around 200-250rnds through it. I'm going to close off the port and cycle each round by hand, take gas out of the equation for now. I feel like I might have it over gassed after researching.

Lapping the upper looks fairly simple and easy since I'm going to be checking the torque specs, might as well do it. Everything seems to function well without dragging, certainly no clunking. I feel like a I should have someone take a look other than me, my tolerances for function are "service grade." Very possible I'm missing one thing or two that are off just enough.

 

[rfk25]

Update. Retorqued barrel nut, new Aero rifle spring and buffer, lapped upper, adjusted gas block. IMI 175gr match. Shot off bipod and support hand wrapped in towel for support. Just quick testing.

 

[bfoosh006]

Very nice, Thanks for updating.

 

[ARKEMAXUS]

Nice, looks like you may have figured it out. I had a DPMS LR308 10 years ago that had amazing accuracy. Only reason I got rid of it was; higher quality options came up that were lighter.

Prone and off a bench has very little, if anything to do with it in your case. Sounds like you know what you're doing prone. I almost never shoot off a bench. It's always prone and I sometimes get .5MOA groups out of some of my rifles but I've been having similar issues to yours with one of my semi autos. Chalked it up to the fact that it's a battle rifle, not a precision rifle.

 

[rfk25]

I will get to a bench because I want to know what it can do, but I’m really happy with this. Time to fine tune with loads and get my skills honed back in. It’s been a minute since I spent real time behind a rifle. Since leaving the uniform, I carry a pistol and shoot clays regularly now.