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Posted: 9/2/2016 4:51:15 PM EDT
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I bought an extra bolt carrier years ago from I don't remember where. The only mark I see is a D on the 6 o'clock of the bolt.
I've run this BCG in every gun I own and still no dice. It usually fails to eject but when it does, it doesn't feed the next round. It makes the rifles single shot. Rack the CH and squeeze the trigger, boom.....click. I've stripped it many times and everything looks good. The gas rings are aligned properly and staggered. I'm at a loss. Help me please. |
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Sometimes the front carrier key screw can break. It still looks good because of the staking but lets gas out and causes short stroking.
Sometimes the ejector can get clogged with small brass shaving and fail to function properly also. Saw one broke/ weak ejector spring that cause failure to eject but not every time. |
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Being a extra B/C, swap the bolt on it with a bolt from a working B/C, and try both B/C's in a rifle.
This will weed the problem down to either the both or carrier being the problem. If bolt, then need to check the demension of it to make sure it head spacing on the barrel correctly, hence distance of the barrel lugs themselves, then the distance from the face of the bolt to the bolt face recess. 
Also, take the bolt and stick it in the carrier all the way without a cam pin, and make sure when you go to pull the bolt back out, it not binding. Hence the bolt does not have a bad machine cut, increased diameter just before the bugle section and this is causing the bolt to bind in the gas chamber section back channel isntead. 
If the carrier, then dry fit the carrier with key (no bolt) to make sure that the carrier key is not biding in the upper receiver channel, the gas tube is aligned with the key to start with. If these are good, the suspect that you have a leak between the bottom of the key to the top of the carrier. Hence either the bottom of key gas passage has a entry channel bur, or the same on carriers gas passages channel, and when the two where bolted together, the bur is causing the leak (or as pointed out, one of the bolts snapped isntead). As for how to some the leak problem, remove the key bolts and throw them away. On the key in hand, use a lapping place with some 400 sand paper, and make sure that the bottom of the carrier is true and bur free. On the carrier double check the gas passage channel for an edge bur that my be proud that needs to be resolve, then with some lapping compound, lap the trued key into the top of the carrier to mate the two surfaces. Now with the bolt surfaces clean, put a drop or two of 272 loctite on the top of the carrier surface (being use to make a thin gasket, and not bolt locker), place the Key in place on top of the carrier and move is slightly front to back to get the 272 to wick across the two's surfaces, and then using new key bolts, tighten the key bolts to 37in lbs (3.08ftlbs), blow down the key channel to make sure that the 272 is clear of both passage channels, and stake the key metal into the side spline of the key bolts (do not try to peen the key bolt heads). |
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The "D" on the bolt is generally found on DPMS bolts. You may wish to contact their customer service, as they are an Industry Partner here.
CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
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Quoted: Being a extra B/C, swap the bolt on it with a bolt from a working B/C, and try both B/C's in a rifle. This will weed the problem down to either the both or carrier being the problem. If bolt, then need to check the demension of it to make sure it head spacing on the barrel correctly, hence distance of the barrel lugs themselves, then the distance from the face of the bolt to the bolt face recess. http://i1286.photobucket.com/albums/a601/AVIDavid1982/headspaceboltdimensionalinspeciton_zpscbb3d395.png Also, take the bolt and stick it in the carrier all the way without a cam pin, and make sure when you go to pull the bolt back out, it not binding. Hence the bolt does not have a bad machine cut, increased diameter just before the bugle section and this is causing the bolt to bind in the gas chamber section back channel isntead. http://www.gunco.net/gallery/data/500/MVC-539X2.JPG If the carrier, then dry fit the carrier with key (no bolt) to make sure that the carrier key is not biding in the upper receiver channel, the gas tube is aligned with the key to start with. If these are good, the suspect that you have a leak between the bottom of the key to the top of the carrier. Hence either the bottom of key gas passage has a entry channel bur, or the same on carriers gas passages channel, and when the two where bolted together, the bur is causing the leak (or as pointed out, one of the bolts snapped isntead). As for how to some the leak problem, remove the key bolts and throw them away. On the key in hand, use a lapping place with some 400 sand paper, and make sure that the bottom of the carrier is true and bur free. On the carrier double check the gas passage channel for an edge bur that my be proud that needs to be resolve, then with some lapping compound, lap the trued key into the top of the carrier to mate the two surfaces. Now with the bolt surfaces clean, put a drop or two of 272 loctite on the top of the carrier surface (being use to make a thin gasket, and not bolt locker), place the Key in place on top of the carrier and move is slightly front to back to get the 272 to wick across the two's surfaces, and then using new key bolts, tighten the key bolts to 37in lbs (3.08ftlbs), blow down the key channel to make sure that the 272 is clear of both passage channels, and stake the key metal into the side spline of the key bolts (do not try to peen the key bolt heads). I thought spec was 56 in/lb for gas key screws. Here is my how to thread on replacing gas key screws: http://www.ar15.com/forums/t_3_4/697684_How_to_fix_a_loose_gas_key___with_pictures.html |
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With new bolts inbound, will be a a breese to correct as I pointed out above. As for the snapped bolt, should be able to use a pick tool to spin it back out.
The torque specs have increased, but 37inlb pounds still works fine, and you don't chance snapping another bolt isntead. hence if the bolts and the keys metal is not up to the new specs, then you just chance snapping new bolts again. As for peen'g the bolt metal into the side of the spines on the bolt, machine tool will give you the factory side type pinching, but not needed. Hence all you really need to do once the bolts have been tighten to 37inlbs, is just flow enough of the softer key metal into the harder bolt spines only. And again, do not try to peen the heads of the bolts into the key in any way, but the softer metal of the key into the sides of the bolt head spines. Note, very old topic, and why you see old bolts that the heads of the them have been peen'd in some fashion. http://www.ar15.com/content/page.html?id=122 So top and bottom staking is fine, but the center carrier staking where the bolt head itself has been peen, bad instead. Hence only does this cause a problem with the bolt loosing there torque to start with, but also can hair line fracture the bolts to cause them to snap again. 
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