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Posted: 5/28/2009 6:19:33 AM EDT
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I have a Bushmaster XM15-E2S that came with a post ban A2 stock. I changed out the stock to a Command Arms collapsible stock with a commercial spec tube & spring that came as a complete kit. Right after I changed the stock I noticed that it took considerably more force to pull back the charging handle. I removed the spring and it measured 10 7/8". I had heard about CCA shipping the wrong springs a while back, but this spring was in the 10 1/16" to 11 1/4" specs so I thought it was just a difference in the age of the springs.
Well, I went to the range and my semi turned into a bolt action with the new stock. There was not enough pressure to hold the bolt back on an empty magazine and while the spent cartridge did extract, the bolt didn't go back far enough for a new shell to be loaded. I then took the CAA stock off and reinstalled the A2 stock. Everything has been working fine since with the original stock. I was wondering if: The CAA spring could be out of spec even though it's the correct length? If the problems with the CAA stock, corrected by the re installation of the A2 stock & spring is a sign of an underlying gas pressure problem somewhere? I really like the CAA stock, but having a bolt action AR bites the big one. Oh, some things I checked so far: The gas rings pass the "tightness test". The gas key screws are tight and staked. Different ammunition was tried to no avail. Does anyone have a picture of what the rear of the gas tube should look like? I have read about the mushroom, but can't visualize what it should look like. I also have to pick up a set of good calipers to measure the diameter of the gas tube to the ID of the gas key. I have no idea how many rounds have been through the rifle as I bought it used from a dealer (and yes I paid way too much for it). I think that's it, but if I left something out I'm hoping someone will let me know. Thanks in advance for your help. ETA: Changed mil-spec to commercial spec and to add kit number of CBST |
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The A2 stock has a longer buffer than a collapsible stock . The kit should have had a short buffer included and the spring is shorter . Sound like you used the long buffer in the tube .
In that case your buffer is bottoming out in the tube . The spring will be totally compressed by the longer buffer even if you use the short spring . Sorry don't have any pics . Stand by getting pics 
you need to use the shorter one of the two in the pic |
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Quoted:
The A2 stock has a longer buffer than a collapsible stock . The kit should have had a short buffer included and the spring is shorter . Sound like you used the long buffer in the tube . In that case your buffer is bottoming out in the tube . The spring will be totally compressed by the longer buffer even if you use the short spring . Sorry don't have any pics . Thank you for taking the time to clarify ARfoxone. Yes, the kit did come with a new buffer (sorry for not including that in my original post) and is considerably shorter than the A2 buffer. |
If you have another carbine spring and buffer, switch it out with the CAA one and see if that is the problem. If not, doulble check the buffer seating into the spring. The last coils on the spring can be tight and not fully seat on the final rim of the buffer which would hold the BCG up a little. (Although after a few cycles it seems like it would seat itself). Anyway, here are three photos: The first is the mushroom on a gas tube just because you were curious, but probably doesn't have anything to do with the problem. The second is the buffer not fully seated on the spring and the third is the buffer properly seated.
  
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Quoted:
If you have another carbine spring and buffer, switch it out with the CAA one and see if that is the problem. If not, doulble check the buffer seating into the spring. The last coils on the spring can be tight and not fully seat on the final rim of the buffer which would hold the BCG up a little. (Although after a few cycles it seems like it would seat itself). Anyway, here are three photos: The first is the mushroom on a gas tube just because you were curious, but probably doesn't have anything to do with the problem. The second is the buffer not fully seated on the spring and the third is the buffer properly seated. Thank you for the post RLR350. The picture of the gas tube helped a lot. I wasn't sure how much mushroom there should be, but I do now and with that I can rule out that possible issue. I think I'm going to try and find another carbine spring. The usual sites are sold out (gee imagine that), but I might be able to get lucky somewhere else. As for the spring/buffer seating, I know I had the spring tight up against the buffer. I wish it were that simple. |
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Well, I just returned from the range and my AR is all set now. I ordered a new carbine spring and installed it before going to the range. An hour shooting holes in paper yielded zero problems. I could tell there was a difference between the CAA spring and the new spring as soon as I installed the new one and the shooting confirmed that the CAA spring had too much tension.
It's nice having my semi Bushmaster back 
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