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Posted: 12/27/2014 1:29:56 AM EDT
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Hello, new member, although I've read topics on here for years and always have found the knowledge of you guys very helpful in my builds or trying to diagnose problems on AR's. I've got a AR that I have been messing with for sometime and it is giving me fits. I've tried everything I know to do with no luck. Any help you guys can give will be much appreciated.
The gun: Aero upper, Midwest barrel, mid length gas system. The lower is a spikes with CMMG parts kit and a POF trigger and a minimalist style non collapsible stock with standard buffer and spring. Problem: I think it's short stroking, but not positive. It will not lock bolt back and it fails to eject 3 out of 5 times. The barrel has been modified. I cut 2" off at put on a fake can style muzzle break on it that I plan to pin on if I ever get it problem free. I've enlarged the gas port in the barrel about 10 thousandth, with no help, I've switched to a adjustable gas block and all the way in or out no difference. I've shot the lower on another upper and it's trouble free. Shooting American eagle 55 gr. brass. What am I missing or what other info do you need to troubleshoot this thing. It's driving me crazy. Thanks for your help |
Sounds like a dwell time issue, meaning that you may not have enough barrel past the gas port to reliably get gas back into the bolt carrier assembly. Sometimes this can be deal with by using a muzzle brake that helps create back pressure, look at something like a Noveske KX3.
CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
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Quoted:
Sounds like a dwell time issue, meaning that you may not have enough barrel past the gas port to reliably get gas back into the bolt carrier assembly. Sometimes this can be deal with by using a muzzle brake that helps create back pressure, look at something like a Noveske KX3. http://www.brownells.com/userdocs/products/p_100003335_1.jpg CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 That's kinda what I was thinking. Wasn't sure what you call it, but that makes since. Just wondering, what's the possibility of going to a shorter gas tube? I would have to machine a slot in barrel for the gas block and then weld the gas hole up, but I can if it would fix the problem. It would be way easier to put on a flaming pig if it would do the trick. |
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Quoted:
2 inches cut from 16" barrel Your still in the hunt, since the 14.5" barrels uses around the same size gas ports as the 16" barrels (read increasing the Gas port by .010 should have had you right back in the hunt with the shortened barrel if it ran before). So on this note, you need to go back and check the gas system for leaks or blockages. Here you may not have the gas block indexed correctly with the barrel port, the gas block to barrel, or gas tube to gas block may be leaking, The carrier key is leaking against the top of the carrier. Also to point out, once you play with the gas block, make to check alignment of the gas tube to carrier key. This is done by just using the carrier without bolt in the upper receiver by hand. Also, make sure that your bolt catch is moving freely (just has spring tension pulling it back down), Shotgun the upper open, install a empty mag in the well to confirm that the empty mag follower is raising the bolt catch all the way up, Then with the upper back locked down, pull the charging handle all the way back to confirm two things, 1. The front face of the bolt stops about 1/8" to 1/4" in from of the back of ejection window with a full pull of the handle. 2. During the last half of the charging handle pull test for bolt back postion, there is not a increase is the tension needed to pull the handle all the way back. If the last inch'ish of the handle pull needs more tension to pull it back, either you have the wrong recoil spring in play and it's coil binding up, or you have hammer wedging going on and the tail of the hammer it too long. |
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Quoted:
Your still in the hunt, since the 14.5" barrels uses around the same size gas ports as the 16" barrels (read increasing the Gas port by .010 should have had you right back in the hunt with the shortened barrel if it ran before). So on this note, you need to go back and check the gas system for leaks or blockages. Here you may not have the gas block indexed correctly with the barrel port, the gas block to barrel, or gas tube to gas block may be leaking, The carrier key is leaking against the top of the carrier. Also to point out, once you play with the gas block, make to check alignment of the gas tube to carrier key. This is done by just using the carrier without bolt in the upper receiver by hand. Also, make sure that your bolt catch is moving freely (just has spring tension pulling it back down), Shotgun the upper open, install a empty mag in the well to confirm that the empty mag follower is raising the bolt catch all the way up, Then with the upper back locked down, pull the charging handle all the way back to confirm two things, 1. The front face of the bolt stops about 1/8" to 1/4" in from of the back of ejection window with a full pull of the handle. 2. During the last half of the charging handle pull test for bolt back postion, there is not a increase is the tension needed to pull the handle all the way back. If the last inch'ish of the handle pull needs more tension to pull it back, either you have the wrong recoil spring in play and it's coil binding up, or you have hammer wedging going on and the tail of the hammer it too long. Quoted:
Quoted:
2 inches cut from 16" barrel Your still in the hunt, since the 14.5" barrels uses around the same size gas ports as the 16" barrels (read increasing the Gas port by .010 should have had you right back in the hunt with the shortened barrel if it ran before). So on this note, you need to go back and check the gas system for leaks or blockages. Here you may not have the gas block indexed correctly with the barrel port, the gas block to barrel, or gas tube to gas block may be leaking, The carrier key is leaking against the top of the carrier. Also to point out, once you play with the gas block, make to check alignment of the gas tube to carrier key. This is done by just using the carrier without bolt in the upper receiver by hand. Also, make sure that your bolt catch is moving freely (just has spring tension pulling it back down), Shotgun the upper open, install a empty mag in the well to confirm that the empty mag follower is raising the bolt catch all the way up, Then with the upper back locked down, pull the charging handle all the way back to confirm two things, 1. The front face of the bolt stops about 1/8" to 1/4" in from of the back of ejection window with a full pull of the handle. 2. During the last half of the charging handle pull test for bolt back postion, there is not a increase is the tension needed to pull the handle all the way back. If the last inch'ish of the handle pull needs more tension to pull it back, either you have the wrong recoil spring in play and it's coil binding up, or you have hammer wedging going on and the tail of the hammer it too long. Thanks for the info, I'll do some checking and see where we end up. Thanks for the suggestions by everybody!!! |
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Quoted:
That's kinda what I was thinking. Wasn't sure what you call it, but that makes since. Just wondering, what's the possibility of going to a shorter gas tube? I would have to machine a slot in barrel for the gas block and then weld the gas hole up, but I can if it would fix the problem. It would be way easier to put on a flaming pig if it would do the trick. Quoted:
Quoted:
Sounds like a dwell time issue, meaning that you may not have enough barrel past the gas port to reliably get gas back into the bolt carrier assembly. Sometimes this can be deal with by using a muzzle brake that helps create back pressure, look at something like a Noveske KX3. http://www.brownells.com/userdocs/products/p_100003335_1.jpg CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 That's kinda what I was thinking. Wasn't sure what you call it, but that makes since. Just wondering, what's the possibility of going to a shorter gas tube? I would have to machine a slot in barrel for the gas block and then weld the gas hole up, but I can if it would fix the problem. It would be way easier to put on a flaming pig if it would do the trick. You could always do a shorter gas system and fill the other gas port as you mention, but I would try the muzzle brake or comp to create more back pressure first, as it would be a lot less hassle. I would also recommend you avoid violating any NFA laws by either registering it as an SBR, or permanently attach a muzzle brake or comp so you barrel is at least 16" in length or more. CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
| The OP mentioned opening up the gas port .010 and then putting on an adjustable gas block when increasing the port size did not help. It should be pointed out that an adjustable gas block will not increase gas flow any more than what the port hole is in the barrel. If the port hole is X and you put on an adjustable gas block, all you can do is constrict smaller than X and decrease gas flow, you cannot increase gas flow larger than X. In the way the adjustable gas block was used here it was wasted money since the OP was trying to increase gas flow. |
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Are you running a rifle buffer in a carbine style receiver extension? When you say "minimalist" style stock I'm not sure if you mean an A1, A2 or CavArms A1 style or fixed "carbine" style stock?
Carbine receiver extensions require the use of carbine buffers. Rifle buffers are too long and will cause issues because they can't go far enough to the rear. When using the charging handle will the action lock open on an empty magazine? If not this is your problem. |
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My first suspicion is that the gas block may be partially obstructing the gas port. It can sometimes happen with a gas block seated all the way against the shoulder on the barrel, which is (usually) located to allow space for a handguard ring. Or it's just not aligned correctly. If you remove the gas block you can usually see a circle of fouling on the barrel which will be where the gas port is in the gas block - the circle of fouling should be centered, or nearly so, on the gas port in the barrel.
Second would be that you have some kind of mixup in buffer/buffer tube/spring configuration... rifle spring in a carbine setup for example. If you're using carbine size parts in a rifle tube, your gas key would be impacting the top of the lower receiver at the back of its travel. |
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