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Posted: 12/30/2011 11:21:22 AM EDT
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So I bought an A2 stock second hand from a local shop who said it was just a takeoff stock and the guy didn't want it after having an adjustable stock put on. I bought it for $40, but then had to buy the spacer and top screw, no big deal.
This stock was for a varmint build and I had purchased a new bushmaster 20" Predator upper to mate to a lower that built itself around my house. Noticed that it felt pretty strong but it was my first rifle buffer system and just figured thats how it was. Took it out last weekend with my wife and burned through 20 rounds of PMX X-TAC, my wife was shooting and when she got near the end, asked if any were left, I said look at the bolt, if it is open, you are empty. The bolt was closed, but she was empty. Tried another magazine, failure to lock back on empty. some unknown mfr tracer rounds would FTF due to short stroking, but would eject fine. We put it away and I figured I didnt lube it well enough. I re-cleaned and re-lubed, tried again. Same thing, would feed ammo, but not lock back. I double checked everything in the gas system, all looked good, and the only thing I could not confirm the origin was the buffer spring. I dug around the net and found the comparison chart and it said the wire diameter should be .072 for a factory spring, rifle or carbine. Measured my carbine. 072. Measured the unknown rifle spring... .077. AND only 39 coils instead of the 44. but it is also 12.5" relaxed Here is the spring in question. Unkown spring on top, New DPMS rifle spring on bottom (which is 44 coils, .072, and smoothed up the bushmaster quite nicely) 
Now I see carbine springs also say 39 coils, but should only measure 11.25 relaxed. couldnt find dimensions on other springs. TL;DR - What buffer spring is 39 coils .077 wire diameter 12.5" relaxed length after racking the charging handle, I am pretty sure my problem will be resolved, but wont get a chance to fire it for awhile. at least it was only a $4 fix |
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Quoted: yes it does, when manually pulling the CH back with an empty mag the bolt catch engages normally. these are all p-mags btw This is what I was talking about. AR-15 » Troubleshooting » Problem bolt catch help That might be a worn carbine spring that somebody pulled to make it longer. |
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Quoted:
Just start with a new / correct spring and be done with it. Makes more sense than spending hours counting coils and measuring.  Which is what I did. But now I have a spare spring, buffer, some grips... Almost a rifle, I just want to be able to label my spare parts :) |
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