Failure to re-feed and sometimes extract. Help!

[XavierRED]

I have a DPMS G2 Hunter. .308 with a 20" barrel. I went to the range today and had a shitty day. Let me start 3 weeks ago...
I shot my rifle for the first time 3 weeks ago. I bought 2 boxes of PMC 147 grain .308 and 2 boxes of Federal 149 grain 7.62x51. The PMC worked great with zero problems extracting or re-feeding, I put all 40 through it. When I tried to shoot the Federal it wouldn't re-feed immediately but would extract... I only shot 12 rounds of this and called it a day.
Now TODAY I brought 100 rounds of CMC/Magtech .308 (I think 149 grain) with me and immediately it wouldn't re-feed and twice it wouldn't extract...
I tried various mags, Pmag and steel, and it still wouldn't re-feed. Is this a gas block problem? Ammo problem? Help me out! Thanks guys!

Wes
Colorado Springs

 

[wareagle700]

Before I say it sounds like it isn't getting enough gas, did you lube the BCG inside and out liberally before shooting? .308's tend to be a bit picky when new and if ran dry.

If lube was not the issue, check gas block alignment. Try some full power .308 win loads with 168-175gr bullets. Those 7.62 loads may not have enough oomph to reliably cycle the new rifle.

 

[mosquitoshooter]

I vote that it's a gas block alignment issue. If the gas block is perfectly aligned, then maybe a gas port issue in your barrel. Not big enough?? I have had many barrels built in 308 and If you were to talk to Krieger barrels they would tell you that 20 inches is the lowest they would recomend building with their barrels in 308. Why? because the shorter barrels don't have enough dwell time to create enough gas back pressure. I know your barrel is at 20 inches but my point is that shorter barrels tend to have more issues than longer barrels. It doesn't mean that shorter barrels are a bad choice, there are just trade-offs.. Regardless, I'm still betting that it's your gas block.

 

[mosquitoshooter]

Another thing, it certainly is a short stroking issue. It takes less gas pressure to extract the spent around then it does to provide enough force to carry the bolt carrier all the way back to strip a new round out of the magazine. If you were to shoot one round at a time, I bet you would find that it extracts the old rounds just fine, but, it doesn't move far enough back for the magazine to lock the bolt open. Also check the gas key on top of the bolt carrier group. Make sure it is tight. Also take the bolt out of the carrier, then make sure the gas key aligns with the gas tube. No Drag between the gas tube and gas key should be the case. Additionally, look at your gas rings on the bolt. Do they look good? Are they staggered the way that they should be? Hope that makes sense

 

[Ballista One]

Sounds like a short stroking problem for sure. As wareagle700 pointed out, a copious amount of lubrication is mandatory. Using some of the ammunition your having problems with, load a single round and verify that the bolt is locking back on an empty magazine. If it isn't, a thorough inspection of the gas system is in order. Did I forget to mention that a copious amount of lubrication is mandatory?

@mosquitoshooter - Staggering the gas rings is unnecessary. There is no gap when the bolt is installed in the carrier. This is one of those urban legends that just won't die...

 

[mosquitoshooter]

Sounds like a short stroking problem for sure. As wareagle700 pointed out, a copious amount of lubrication is mandatory. Using some of the ammunition your having problems with, load a single round and verify that the bolt is locking back on an empty magazine. If it isn't, a thorough inspection of the gas system is in order. Did I forget to mention that a copious amount of lubrication is mandatory?

@mosquitoshooter - Staggering the gas rings is unnecessary. There is no gap when the bolt is installed in the carrier. This is one of those urban legends that just won't die...

Good to know, thanks. I've never tested with the gaps fully aligned but it does make sense that when you put the bolt in the carrier, Because the rings are compressed, there is no gap