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Posted: 8/4/2008 8:03:50 PM EDT
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Good evening, I searched back 3 pages and found nothing like my problem, so here goes. I bought an RRA NM upper last year and have been using it in competition for the last two seasons. It is attached to a Bushmaster lower with an RRA/WOA two-stage trigger in it. Additionally, I installed a Tubb CWS. The rifle will not lock back in single fire or rapid, but does manage to come back far enough to strip and feed a new round in the rapid stages. I have changed the bolt catch and spring for a new one. No joy. Swapped bolt carriers. No luck. Removed the CWS. Same story. (This is with the ridiculously hot loads High Power guys like) The buffer spring is practically new, only about 1,000 rounds on it. Sometimes the bolt catch will snag the carrier instead of the boltface, locking it back sort of, however, when I rock the rifle over to drop in a new round, it snaps shut. I have tried several different magazines, new NMHTGs, Adventureline, a Bob SLED, and a Sinclair follower. Not one of them works to get the rifle to lock back reliably. I cannot tell what the hell is going on with this thing and I have a regional championship coming up in 2 weeks, so any help will be appreciated. Thanks |
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Pull the FSB and confirm that the barrel was indexed correctly (gas port set TDC to the receiver). If it was not, could be that when you Zeroed out the FSB (set screws) you blocked the gas port (burn mark around the barrel gas port should have the port in the dead center of it). As for the tubbs system, if you have the action tuned for the ammo being used, it's never needed. If you have the action set light for light ammo, and need the extra weight for hotter ammo, then it does have some merit there. |
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I don't have an adjustable front base. Be cool if I did. I pulled it apart about 300 rounds ago to fix a couple of things in the barrel, and when I did that it seemed that the gas port and base were slightly mis-aligned but the gun had functioned 100%. I just now pulled the base back off to see if it had gotten messed up during reassembly, but it's just like it was before. Like I said, I'm at a loss to explain this problem. |
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Confirm that the bolt is entering and exiting the barrel extension without binding. The barrel could have slipped index when you tightened the barrel nut on reinstall. And, when did RRA stop using set screws on there NM Barrel FSB's to allow them to be adjustable? |
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You might want to take a look at the bolt catch again. Check to see if there is a lot of play between the bolt catch and lower receiver. If there is a lot of play the bolt catch can actually slide off the follower or catch the very back end of the follower causing the bolt catch to engage the bolt carrier in stead of the bolt face or not catch at all. pull your upper off and grab the top ot the bolt catch and see if you can move it front to back. It should move very little. Put an emply magazine in and see how much the bolt catch engages the end of the follower, the final test, see if you can push on the bolt catch and make it slide off the follower. Hope this helps Scott |
It's doing it with all loads. I may have a chance on Saturday to get it looked at with a borescope so I can check out the gasport alignment, it feels like it's under gassed, like the bolt is just not making it back far enough for the catch to engage. |
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