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Posted: 8/7/2007 1:39:59 AM EDT
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I bought a DPMS 16" barrel A-4 style AR . One of the gas rings broke with only about 500 rnds through it . I replaced the rings and put another 400 rounds through it . The bolt was tight when I installed the new rings but after the 400 rounds it isn't tight . The bolt carrier wont stay up when you put the bolt face down . I read that the bolt carrier should stay up when placed up right and if not it's time to replace the rings . The rifle shoots fine , cycles properly . Is it possible that my assembly is just loose ? I plan on shooting it and seeing what happens . My other half has a bushmaster and the carrier assembly is much tighter . Are DPMS carrier assemblies just a looser tolerance ? Any help would be greatly appriciated . Eric |
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Welcome to the site, Eric. Just to clearify, the Bolt should stay in the carrier when the Bolt Carrier Group (BCG) is out of the gun with the BCG held bolt down (is this what you meant). Look inside the carrier at the cam pin hole area, you may have a burr that is damaging the rings. Also check the lip just inside the carrier opening for a sharp edge. Also, make sure you lube the rings when you install them. If your bolt will not stay in the carrier with ring pressure alone, you could run into maflunctions if you take it to the range (just a note). Hope it helped. |
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I had one bolt carrier, a Smith, that would eat regular rings. It would usually break the end off the last ring. Every time. I could not detect a burr in the bolt carrier, and after careful cleaning and examination, careful reassembly, it would happen again. Even though breaking the last ring, it never malfunctioned. There were two possible solutions. The expensive solution was to simply replace the bolt carrier. I didn't do that. The cheap solution was to replace the rings with a McFarland spiral ring. That was done, and has not been replaced since. |
First, remove the bolt from the carrier by removing the firing pin retainer (cotter pin under aft end of gas key). Turn the carrier, bolt "up" and the FP should fall out (might need a tap). Push the bolt back into the carrier. Turn cam pin 90 degrees (to clear gas key) and pull out. Now the bolt can be removed from the carrier. Using a pick, working rings off back of bolt, gently lift one end (rings are split) of the back ring over the retainer edge (helps to push on the other side of the rings to hold them still. Push straight in on them) and "roll" it out by sliding the pick round the bolt . Continue with the next one, then the last one. Just be gentle, unless you are NOT going to re-install them. To re-install, reverse the order. Place one end of the ring into the retainer edge, and "roll" it in. After you have re-installed them all, apply lube to rings and re-install bolt in carrier (will take a little push) and assemble carrier in reverse order. NOTE: extractor goes on the side that the spent cases leave the rifle (the cam pin should not enter the bolt if it is installed incorrectly, but if your pin or bolt is worn, it could be possible). If you have trouble re-installing the FP retainer pin (cotter), try twisting it, it should go in till the head of the pin it flush with the carrier. Replace it if it appears bent. Hope that helped. And, sorry to OP for hijack. 
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To add to the above detail, A thumbnail instead of a pick will less likely end up with you bending or snapping a ring as your ride the rings in or out of the annular retaining groove of the bolt (one ring at a time). Since the rings are stamp cut, one side of the rings will have rounded edges, with the other sides sharp edges. When you stack the rings, the sharp/bottom stamped edge of the rings will direction towards the back of the bolt (where the FP enters, and all the rings installed the same edge direction). The reason for this is the sharp edge will seal better than the rounded edge until the rings break in/mate to the carrier walls. http://www.ar15.com/content/manuals/TM9-1005-319-23.pdf Pages, 3-21 and 3-24 Covering install and removing bolt gas rings. Also, on the cotter pin/FP retainer install direction, the split in the pin should be direction front to back, not up/down in the bolt. Granted it really doesn't make that big of a difference on in-spec retainer, but on some of the off brand softer type FP retaining pins that go south in a thousand rounds if installed without being directional this way, it gives them a bit more serviceability life. |
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