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Posted: 12/17/2007 6:39:12 PM EDT
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I usually shoot 75gr or 77gr bullets out of a 20 inch barreled AR. I recently loaded up some 60 grainers and found the bolt was failing to cycle - the bolt comes back but not far enough to pick up the next round in the mag and then slams forward on an empty chamber. I am using a max load of Varget (27grs). I can't understand why it cycles properly with heavier bullets but not at all with these lighter bullets. Anyone else had this problem? |
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A lot of the heavier bullets in .223 can not be seated to mag length, and are used single shot. If this is not the case, then disregard. Your magazine might be at fault try a different one. You might have bought some bullets that were .223 dia instead of .224 dia and it is not making a good seal in the bore. You may have a Heavy buffer/spring and need a lighter one. Will the bolt lock back on an empty mag/last shot? Check your key it might be loose. |
| Thanks, but how does excessive pressure cause the bolt not to cycle? My cases do have ejector marks but I put that down to a new bolt and a rough face on the ejector stem. The primers are flattened which I suppose indicates the load is on the hot side - but I still don't get the mechanics of the bolt not cycling as a result. |
When the load goes over the top, the residual barrel pressure causes the spent case to the chamber walls at bolt unlock to be too strong/great for a normal cycle/pull (extractor being able to pull the case out of the chamber cleanly at unlock) and a great deal of B/C’s rear momentum is lost on pulling the spent case out of the chamber alone. We refer to this as over cycling, and can be caused by the load going over the top, using powder that burns much to slow for the system, or just have a gas port much too large for the load at hand. |
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