DPMS LR 260 - Gas Block Question - Possible Leak?

[CPRifle]

I shot my new DPMS LR260 today for the first time. Overall I'm impressed, but the rifle did have a hard time cycling (short stroking) with a particular handload. The rifle did cycle and pick up the next round with Rem factory core-lokt (every time).

I figured the problem was with the handloads being under powered, however I did see some residue around the gas block and thought I should ask this forum's thoughts.

Here are the pics. Thanks.

 

[danr]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

Same thing happened with my very first LR-308 but in my case it was'nt so much a leak it was the that the gas block had not been properly aligned with the barrel's gas port. I took it off cleaned it and set it back directly over the gas port and never had feeding/cycling issues again.

 

[8up]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

Agree with what danrodder said. Check alignment of your gasblock to the gas port. Make sure the gas block screws are tight and have not worked loose. The gases are leaking in your pic's.

 

[CPRifle]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

One of the two allen screws was a bit loose... not significantly, but I did get an additional 1/8 turn on it.

Any idea on what the torque spec is for the two allen screws?

How do I when the gas block is properly aligned?

 

[CPRifle]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

I took the gas block off, cleaned it up, and re-installed it square to the receiver rail. Both allen screws are now 'snug' (about as much force as I can apply with a little allen wrench).

I also noticed that the buffer tube / spring were completely dry and not lubed. They are now, and the rifle feels smoother when using the charging handle.

Thanks for the advice. I'll reply with a range report after the next time I get out.

 

[Pat M]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

they run better lubed good.
that looks like x2 residue compaired to my DPMS 260.

 

[Casey Simpson]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

Red Lok-Tite the allen screws. A little heat from a bic lighter gets em off when you're ready.

 

[CPRifle]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

I just got back from the range. After the minor adjustments mentioned above (tightening the gas block screws, blue loktite, lubing the buffer spring, the same load would now cycle properly, except the bolt hold open catch wouldn't latch. The brass lands right next to the shooter.

When I switched to a handload I'm developing the rifle functions 100% and throws the brass much further.

Regardless of the load, the above suggestions did help out. Thanks!

 

[8up]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

Glad it worked out. Maybe the those loads before were not optimal for the gas operation. Was the gas leakage problem fixed as well?

 

[Afghanvet09]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

I've seen this phenomena also on a guy's rifle...wondered if the barrel diameter underneath was slight out of spec, and the gas block was not making proper seal? I've measured his barrel's outer diameter with calipers and found the contour was not consistant in sections that are suppose to be the same spec/diameter.

 

[bohem]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

Both mine and a buddy's LR-260's do exactly this.

What load were you running that was short stroking?

I've had my gas block off a couple times to do work on the rifle (muzzle threading, coating, etc) and it still continues to sneeze around the barrel like that.

I put an internal mic across the gas block and on the OD of the barrel, the gas block runs 0.9372-0.9374 and the barrel is 0.9358 at the interface. I think it's just a matter of tolerances involved in a mass produced rifle.

It does shoot like a house on fire and I have no troubles with it short stroking or feeding on my handloads or factory loads. The subsonics that I've been launching with it have just enough gas to unlock the receiver but not start to cycle it. Makes for easy manual cycling.

 

[Afghanvet09]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

That's about .0016 inch difference if my math's correct. IIRC, there should be about .001 inch difference, (e.g., gas block is .750" and so barrel should be .749" [.001 difference]) for good fit. Maybe someone who does barrel work can chime in.

 

[CPRifle]

Re: DPMS LR 260 - Gas Block Question - Possible Leak?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 8up</div><div class="ubbcode-body">Glad it worked out. Maybe the those loads before were not optimal for the gas operation. Was the gas leakage problem fixed as well? </div></div>

Mostly... there is still some residue foward of the gas block (muzzle end), but not as much as before.

The loads that were short stroking, were not mine (came with the rifle) and were: 129 SSTs, 40.5gr H380, mag primer, FC brass. I'm not happy with the peformance of this load at all (around 2-3" groups at 100 yards). I worked up 5 loads with 142gr SMKs and H-4350 from 41.9-43.1, they all cycled the bolt properly and are around 1 MOA.