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Posted: 8/23/2015 3:10:56 PM EDT
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I just finished up a new build for 3Gun, and I'm having problems with it. The gun will chamber the first round manually with no problems, and fire that round, however, it will fail to extract and chamber a new round every single time. I tried a different lower to pinpoint the problem to the upper. It functioned the same with the different lower.
The buffer in the first configuration is a non marker buffer that came with the Magpul Stock kit from DSG Arms. I also tried a different bolt. No change. I also tried a "H" buffer. The gun fired and would eject the round with the "H" buffer, however, it still failed to pick up the next round and would go forward on an empty chamber. The specs are: 18" rifle gas length Faxon Barrel, with a rifle length gas tube A slick side upper from MAS Defense MI rail AIM Bolt Nordic Components Corvette Comp. PMC Brass ammo, which shoots fine in several other AR's I have. What buffer should I be using? Any known problems with the 18" Faxon's? Problems with the upper? I'm at a loss here. Thanks |
| Sounds like there is no gas going back to the bolt to operate it. I'd check the entire gas system, especially the gas block. The gas port/hole in the barrel probably doesn't line up with gas port in the gas block. Check the gas block first to see if it was mounted crooked, or mounted too far forward or backward. |
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Quoted:
I just finished up a new build for 3Gun, and I'm having problems with it. The gun will chamber the first round manually with no problems, and fire that round, however, it will fail to extract and chamber a new round every single time. I tried a different lower to pinpoint the problem to the upper. It functioned the same with the different lower. The buffer in the first configuration is a non marker buffer that came with the Magpul Stock kit from DSG Arms. I also tried a different bolt. No change. I also tried a "H" buffer. The gun fired and would eject the round with the "H" buffer, however, it still failed to pick up the next round and would go forward on an empty chamber. The specs are:cd 18" rifle gas length Faxon Barrel, with a rifle length gas tube A slick side upper from MAS Defense MI rail AIM Bolt Nordic Components Corvette Comp. PMC Brass ammo, which shoots fine in several other AR's I have. What buffer should I be using? Any known problems with the 18" Faxon's? Problems with the upper? I'm at a loss here. Thanks The lower should not have any effect unless it is so far out of spec that the inserted magazine binds the BCG or BCG travel is impeded by the BCG hitting the front edge of the receiver extension. Either of these are unlikely, as you would not be able to charge the gun or insert a loaded magazine on a closed BCG with either these conditions present. The DSG buffer you have is a standard carbine buffer and the DSG action spring is a standard carbine action spring, so they are not the issue and should function fine as the increased mass of an "H" buffer actually provides more resistance to BCG movement. You have a gas problem. Either gas is not getting to the gas key on the BCG or your gas key is not secured properly (gas key screws not tightened or sheared) or there are no gas rings on the bolt. Make sure the gas block is aligned and there is no obstruction in the barrel gas port. Make sure the gas port in the gas tube is facing the gas port in the barrel. make sure there are no obstructions in the gas block and gas tube. Make sure the gas key is secured properly. Check the gas rings on the bolt (it should still function with only one gas ring.) |
| Definitely sounds like it's short-stroking, which is indicative of a gas issue. What gas block are you using? How did you verify the alignment? Provided there are no leaks and you have good alignment I'd next try some different ammo. I'm not sure how the PMC stacks up but it might be slightly under powered. |
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I've tried two different BCG, one new one, and one with a couple hundred rounds under its belt. Short troke on both.
I measured the distance from the barrel shoulder to the gas hole, and the distance to the hole in the gas block. Its made so the gas block fits against the shoulder. The gas block is the factory gas block that came with the barrel from JoeBob Outfitters. I'll try different ammo, but I still think its something gun related. |
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Using different ammo will help tell you whether or not it's the gun. So will trying different magazines - you didn't mention this, but it's important. A magazine that drags on the bottom of the carrier can cause a lot of issues, including short-stroking. Trying the gun with a single round of the current ammo in the magazine is a first step.
It sounds like the BCG's not getting quite far enough back. That could be gas, it could be the way the upper is lubed, it could be both. Since you have used a different bolt, I don't think that the problem is due to the original bolt itself, BUT how about the carrier? With a brand new build, running the carrier really WET helps a lot. The carrier's fit to the bolt and the upper are critical points that can rob a system of some of the power it needs to run. |
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Sorry, should have clarified better, I've tried a different complete bolt and carrier.
I've also tried with two different mags. If I load one round into the gun, then remove the mage, it doesn't go back far enough to lock open the bolt. I'll try to take the gun apart tomorrow to check the gas port in the barrel, and to verify that the gas tube doesn't have an extra hole in it I didn't see when I put the gun together. Other than that, I'm at a loss why I'm not getting enough gas. I lubed the gun up very wet with CLP before I started shooting. |
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Quoted: I'll try to take the gun apart tomorrow to check the gas port in the barrel, and to verify that the gas tube doesn't have an extra hole in it I didn't see when I put the gun together. Other than that, I'm at a loss why I'm not getting enough gas. |
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Check the gas tube for obstructions; it is rare but not unheard of.
More likely the gas port is small and requires ammo with high port pressures like the IMI Razor. I have heard some manufacturers do this for recoil control. I had to go to a std spring and H buffer with my 18” rifle gas barrel. |
| Like others have said, it is a gas problem. It was asked, how did you check to make sure you have good gas flow? Just because a gas block looks like it is lined up, it does not mean that it is. When I install a gas block, I will squirt a heavy amount of Gun Scrubber down the gas tube to see how well it flows out of the barrel. If it trickles out, poor flow and poor alignment. If it streams out, good to go. |
| I will mimic what others have suggested and try 5.56 ammo first just to eliminate that variable. I had a factory new 14.5" KAC Mod 1 upper that was having the same exact issues with Independence ammo but, would run 5 other brands of ammo of the same bullet weight with no issues at all. After about 300 rounds of running the ammo I knew functioned 100%, it started to run the Independence ammo without issues. Could be that your barrel just needs a little break in before being able to run the PMC. |
Tried some hotter ammo this morning. Apparently(I knew) the Wolf just didn't have enough steam. This ammo ran 100% without any problems, even locked the bolt back after the last round. I had even put the heavy buffer back in after the Wolf wouldn't run with a standard carbine buffer. Will continue to run milspec ammo for a few hundred rounds and then try Wolf. OP: try running some hotter ammo as others have suggested here. Thanks to all that posted, sorry for the hijack of the thread.
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A blast from the air gun thru the gas tube before installation.
I mark center lines on the barrel and block, add a spacer for the blocks that need to be spaced away from the shoulder. Also depending on the type of block check to make sure it is dead on level with the rail on the upper. |
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Quoted:
Check to make sure you are running the correct buffer with the buffer tube. An H buffer is way lighter than a rifle buffer. I don't think the buffer is the problem. A lighter one may help it cycle, but it should be cycling with a heavier buffer. IMHO, it's like others have said, it's either a gas problem, or the BCG has some kind of unnecessary drag on it. |
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