308 AR Bolt Wear - Is this normal?

[Arne K]

DPMS LR-6.5 Creedmoor with ~400 rounds through it.

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[Member 34319]

Looks fine to me. That side of the lugs is not the part that is taking the pressure anyways. So that chunk is probably from early on when it was fitting itself to the barrel extension. The other side facing away from the picture, is the side that engages similar lugs on the barrel extension and taking the pressure.

 

[Arne K]

Thank you. I'm working on resolving a gas problem and just wanted to be sure the wear pattern on the bolt lugs wasn't pointing at another issue.

 

[P7M13]

6.8 SPC, >2000 rounds:

 

[Member 34319]

Front of the bolt isn't the picture you want, try the back of the bolt.

 

[Arne K]

Back of the bolt is slightly boogered up but not like the front.

 

[drstrangelove]

Looks like a mismatch. Time for a new BCG or BCG head. How do the corresponding barrel locking grooves look?

 

[Ops]

dpms isn't known for top tier parts

 

[Arne K]

I now know that DPMS is highly questionable quality. I bought this rifle new about 8 years ago and won't buy another DPMS product. However, I won't try to offload it to an unsuspecting buyer and would rather fix it than taking a loss and starting over.

 

[P7M13]

That looks rough. Do you have a USB camera? Glad to loan you one of mine if you're in the Beaverton/Hillsboro area.

 

[Arne K]

I think it's more dirty than rough. I run it extremely wet to get it to function and also didn't clean it before taking pics so that wear points might be more visible. What's a USB cam? A quick search gives me spy cams.

 

[P7M13]

Endoscope

 

[FullMetalJerk]

I'd avoid new "DPMS" stuff and stick with older DPMS. After the "Freedom Group" bought up DPMS, Remington, Henry Rifles, Barnes ammunition and a few others the quality went downhill quite a bit. Barnes ammo had the bullets falling out of the cases, the Remington R51 was garbage and their shotguns aren't what they used to be. Remington ammo on the other hand is fine from what I can tell, just slightly underpowered.

 

[Eveskcige28]

What kind of gas issue are you experiencing?

 

[oli700]

DPMS LR-6.5 Creedmoor with ~400 rounds through it.

View attachment 659453 View attachment 659454

looks like one of two things there , bad heat treat or your rifle is unlocking way too fast........or a combo of both . Either way it is excessive for 400 rounds

 

[2A2Dend]

What someone has yet to say is, barrel/bolt mis-match. Not a matched pair. IOW, grab a BCG and toss it in there.
In your case, filing those rough spots away, can help the break-in. Keep putting oil, and the rounds to it. 400 rounds is just getting started.

 

[Member 34319]

That's fairly typical issue. The bolt isn't exactly perfectly matched to the barrel extension. That's why one lug looks worse than others. It's literally taking more of the pressure than the rest of the lugs. One of two things will happen, over use the lug will fit itself to the barrel extension, or that lug will break under stress as it is the only lug really engaging with the barrel extension.

Also, just like the first set of pictures, the parts of the barrel extension you can see, are not the sides of the extension that you need to be examining. The parts facing the chamber are the parts that mate up against the back side of the bolt.

I too will be curious to hear the issues you are having with this gun.

Otherwise this issue with the bolt is very common as AR15s are assembled everyday with parts that are not a 100% match.

 

[Arne K]

The rifle seems to be under gassed. It short strokes, frequently not stripping a round out of the mag or grabbing the top of the case and jamming. It doesn't lock open on an empty mag when fired. Factory mag and 2 different Magpul's give the same results. It does lock open on empty mags when cycled manually. Buffer, recoil spring, and extension tube are correct for the rifle. Gas leakage at the block is minimal and system is clear. I believe the problem is that the gas port is undersized. It measures. 081" and every manufacturer I can find specs port sizes from .086-.097".

 

[Member 34319]

Very unlikely, but a mismatched bolt could be causing this. If the bolt isn't able to come out of battery as it is supposed to, it could be the culprit.

If the action is opening, but short stroking. Adding gas by opening up the port, or loosing weight by reducing buffer weight and spring tension help.

It wouldn't hurt trying a new bolt first. At least that's way you could upgrade to a dual ejector.

 

[Arne K]

This is probably a dumb question but if the issues is a mismatched bolt, how would installing a different random bolt help? Is the idea that it couldn't be worse but might be better?