This is the first mechanical issue my Rock River has given me… The bolt isn’t locking back all the time when I fire the last round out of the mag. It does this with all types of ammo, and if I had to guess it only locks back maybe once or twice out of 10 mags.
I know for a fact the gas key is still staked in tight, no debris blocking it off, etc. My gas rings are staggered and in good shape… Everything is clean. I have only put around 900-950 rounds through this gun since bought new. Although I don’t know if it would even be a problem with the gas system, because if it were, wouldn’t I be having issues with more than just the last round out of the mag?
Yes I am using PMAGS, and it happens with any of the 8 that I have on my chest rig. I will trim a few and then use my USGI mags that came with the gun and see if the problem is eliminated.
The mags are always something to look at when this happens, but it you have tried several already, next up is the gas system. This is often an indicator the gas key is leaking (sometimes hard to see), gas rings are worn or gas pressure is being lost or obstructed elsewhere.
It has done this with Monarch brass cased ammo from Academy, Federal XM855, Remington UMC, and Wolf - all 55grn projectiles.
The buffer tube is stock, so I’m not sure what weight it is. My bolt locks back fine when manually locked using the charging handle if there is an empty mag in the well, and if not I can just lift up on the Magpul BAD lever to lock it… It’s just the last round in the magazine that keeps it from locking back after firing. And with or without the Magpul BAD lever installed, there is no stiffness in the bolt catch when releasing.
After close inspection it doesn’t seem like the rear tabs on the PMAG’s would interfere with the bolt catch, but I trimmed one off with the Dremel tool anyways and will try loading a single round in it, as well as my USGI mags and see if the bolt locks to the rear using those mags.
If the problem continues I will just call Rock River. I’ve already e-mailed them and they said they will pay to have it shipped in for inspection/repair so I wouldn’t be out any money… Just without my AR for two weeks :sad:
Yeah, I don’t really expect the problem to be fixed when I try this trimmed PMAG and the USGI mags. So I have a feeling I’ll be sending it in for repair next week.
It’s a problem I’ve had with my recent builds, whether I was using USGI mags, PMag 20s or 30s, or Lancers. What I think it might be, in my case anyway, is that the bolt catch - bolt catch pin - lower receiver fit was too snug. Quality parts were used, though; G&R LPK, lowers were Mega and Noveske. In fact, the issue came up when I started using exclusively G&R LPKs. What I did on my current under-construction build was use a bit of metal polish, cotton rag, and a few episodes of a good TV show to polish out all interacting surfaces, including the exterior of the roll pin itself. When I installed it all and lubed it, it worked perfectly, as I’ve seen factory bolt catches do. No rubbing or binding.
Not saying that’s what’s going on with yours–in fact, I might have to modify a couple of PMags I’ve got laying around–I’m just sayin’.
does your rifle have a pinned front sight/gas block? Is it tight?
I ask because when I completed my built I was getting random failures to lock open on the last round. My issue was that it was undergassed because I did not have the gas block aligned properly. Once I fixed that it has run fine 100%…all unaltered 30 round PMAGS in mine.
may not be your issue, but its one more thing that can be checked if nothing else pans out.
one of the tech support guys at RRA emailed me and said my gun should be shipping back to me today. He said their was a metal burr somewhat blocking the hole in the barrel for the gas system… Something I didn’t really expect but I’m glad they identified the problem quickly. I’m eager to get it back and start shooting again!
Please, stop, do not modify the PMAGS. Lets think about this first. I have never heard of anyone having to “modify” a PMAG so it works correctly with their rifle. Don’t just modify the mag, think about it first. Just my .02
Good thing someone caught it before it broke loose.
Seen it happens last summer on someone’s brand spankin new Brushwhacker within the first 2 mags through it.
The chip came lose, travelled down the gas tube, through the key, and found its way into the rings and pretty well screwed things up from there.
After beating the thing mortar style on the ground pretty hard more than a few times, (with a bit of satisfaction doing it BTW), to try getting it unlocked it finally let the bolt move enough to try and seperate the upper and lower to strip things down and make repairs.
Chip was found kinda hung on the back shoulder of the ring groove and two rings were all but smeared outside the groove after the chip lifted thier ends a bit and gas pressure + lack of actual clearance did thier work.
Found out later that someone else had inspected it when right out of the box, saw the chip hanging in the bore, but put it down to ‘just a gas port shadow’.
No running a brush through, no straightness gauge check, not even a blast of compresed air/carb cleaner/brake cleaner/whatever through the system to see if anything was inadvertantly trapped in there, just ‘nah, its nuthin. its supposed to look like that, go to the range’
New ungouged carrier, new rings, slight honing stone dress of the bolt where chip stuck on, new buttstock plate (did I mention mortaring the shit out of it? :)) and he has finally gotten more than 100 rounds downrange with it, but is already looking into something more along the Colt, BCM, DD, etc. line to have for a quality keeper rifle and plans on just using this as a beater unless someone comes along and offers to buy it 'cause he certainly doesn’t trust it enough to wonder what might go tits up on it next.
