Ruger AR 556 MPR First Shots

[jmorris]

Been reading good things about it and got a sale email last week featuring it. But then found it cheaper at Sportsman Outdoor Warehouse ($649, no tax, no shipping) and ordered it. Hit the range today. Started zeroing and after about 15 shots something didn't feel right. Then a couple feeding problems. Then I discovered the bolt had only gone about halfway back. I manually cycled and fired it a few time until the bolt barely moved back after a shot. Broke it down and checked everything and couldn't find anything wrong. Relubed and reassembled, still the same problem. Had an idea but not the tools to check so headed home. If you want to take a guess I put some space here before the explanation.
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The gas block shown below should be snug against the ridge. Evidently it wasn't tightened down enough and slowly moved forward. Moved it back and tightened the screw down. Will test fire this weekend.

[Jusme]

I was going to guess a gas block issue. During my stint selling guns, we had this issue, on some ARs. I don't recall any with the Ruger, but a few with DPMS, low profile gas block models. We would advise our customers, to check the torque on the gas blocks, before shooting them.

[jmorris]

Ugh. Held with a set screw? Just me, but I'd back the screw out, set back and center the GB(as you have), and drill a ~1/16" detent for the set screw, then degrease and LT Red it in place.

At this point I've just tightened it down. Ran about 40 rounds and no movement. If I see any I'll try that.