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Rifles, Reloading, Optics, Equipment
AR15/10 Rifles
AR10 cycling problem
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<blockquote data-quote="tim_w" data-source="post: 1820069" data-attributes="member: 11132"><p>So to understand. You first time out with the gun it cycled fine for 5 shots then stopped cycling using the same ammo.</p><p></p><p>You mention AR10 then the upper you used. Many people use "AR10" to describe all large frame ARs. As you can see their are basically two main variants. Those patterned after DPMS/Knight and those after Armalite's AR10. So what is your lower give us and manf or do you know which pattern? Overwhelmingly DPMS is the most used They Aero upper you have is DPMS patterned. I am hoping you just used AR10 as a descriptor. Assuming that is not an issue moving on..........</p><p></p><p>You have a 20" and by your measurement its a rifle gas port. Normally the port for 308win is around .085- .098 for .750 diameter rifle length 20". If you have or can get a drill bit set that is on wire size try bits between size 40 (.098) thru 46 (.081) (large number is smaller diameter). Drill bits are the fast cheap way to get very close to spot on. Use the shaft section. But the size you estimated is inside the normal range. Just remember small changes in port size create large charges in gas vol and @ carrier psi.</p><p></p><p>Given your work on the gas block etc it does not sound like that. Same with the gas tube. Not saying the tube is correct but given the fact it was running and then stopped indicates something changed. Given that lets just temp rule out those two out and check some other things that will be clear if they are the cause.</p><p></p><p>Farmboy is onto something, as other than what we temp rules out above, there is only one area that can really change and its in the bcg. The most likely one is the gas key's allen head screws have come loose or sheared.. </p><p></p><p>First look and see if the screws /key were actually staked. Ideally they would be staked and counter staked. If they are not that needs to be done when finished. But either way check the screws with a tq driver. Its possible they used cheaper weaker grade 5 screws. Grade 8 is proper. 55-58 inch lbs. I use and very much prefer torx head grade 11.5 @ 60inlb screws. No risk of stripping the allen head. They have ribbed outwall which grabs staking better. Also no standard vs metric size issues. </p><p></p><p>. Actually check it against bare glass to see its flat. If it came loose and was fired it could have been warped. If it is order a new one and a couple extra is not a bad ideal to have around. I also take the gas key once its off and lightly sand its base over a piece of glass to insure its flatness for mating to the carrier flat</p><p></p><p>If you find a screw/s loose not sheared replace them regardless as they could gave stretched.</p><p></p><p>The other less likely is the gas rings on the bolt tail are loose to the carrier fit. Stand the carrier on end with the bolt extended. It should not compress under its own weight. It should take some downward force from your hand.</p><p></p><p>Another recommendation (off topic) to ensure smooth initial operation of a freshly built AR or any gas gun for that matter and what I did with every AR I built and sold was to oil the bcg up heavily and then manually cycle it by the charging handle a min of 500x. On high ends builds I did 1000 cycles. It laps and smooths all the contact areas and breaks in the action so it cycles much smoother from the start instead of taking 10-20 mag loads.</p><p></p><p>I used to have the whole family sitting watching TV with towels on the floor cycling ARs while we watching TV 3 days a week to keep caught up. </p><p></p><p>So first thing is lets make sure you have same pattern upper and lower.</p><p></p><p>Next check and see what drill bit shaft fits in the gas port.</p><p></p><p>Inspect your bcg screws and staking.</p></blockquote><p></p>
[QUOTE="tim_w, post: 1820069, member: 11132"] So to understand. You first time out with the gun it cycled fine for 5 shots then stopped cycling using the same ammo. You mention AR10 then the upper you used. Many people use "AR10" to describe all large frame ARs. As you can see their are basically two main variants. Those patterned after DPMS/Knight and those after Armalite's AR10. So what is your lower give us and manf or do you know which pattern? Overwhelmingly DPMS is the most used They Aero upper you have is DPMS patterned. I am hoping you just used AR10 as a descriptor. Assuming that is not an issue moving on.......... You have a 20" and by your measurement its a rifle gas port. Normally the port for 308win is around .085- .098 for .750 diameter rifle length 20". If you have or can get a drill bit set that is on wire size try bits between size 40 (.098) thru 46 (.081) (large number is smaller diameter). Drill bits are the fast cheap way to get very close to spot on. Use the shaft section. But the size you estimated is inside the normal range. Just remember small changes in port size create large charges in gas vol and @ carrier psi. Given your work on the gas block etc it does not sound like that. Same with the gas tube. Not saying the tube is correct but given the fact it was running and then stopped indicates something changed. Given that lets just temp rule out those two out and check some other things that will be clear if they are the cause. Farmboy is onto something, as other than what we temp rules out above, there is only one area that can really change and its in the bcg. The most likely one is the gas key's allen head screws have come loose or sheared.. First look and see if the screws /key were actually staked. Ideally they would be staked and counter staked. If they are not that needs to be done when finished. But either way check the screws with a tq driver. Its possible they used cheaper weaker grade 5 screws. Grade 8 is proper. 55-58 inch lbs. I use and very much prefer torx head grade 11.5 @ 60inlb screws. No risk of stripping the allen head. They have ribbed outwall which grabs staking better. Also no standard vs metric size issues. . Actually check it against bare glass to see its flat. If it came loose and was fired it could have been warped. If it is order a new one and a couple extra is not a bad ideal to have around. I also take the gas key once its off and lightly sand its base over a piece of glass to insure its flatness for mating to the carrier flat If you find a screw/s loose not sheared replace them regardless as they could gave stretched. The other less likely is the gas rings on the bolt tail are loose to the carrier fit. Stand the carrier on end with the bolt extended. It should not compress under its own weight. It should take some downward force from your hand. Another recommendation (off topic) to ensure smooth initial operation of a freshly built AR or any gas gun for that matter and what I did with every AR I built and sold was to oil the bcg up heavily and then manually cycle it by the charging handle a min of 500x. On high ends builds I did 1000 cycles. It laps and smooths all the contact areas and breaks in the action so it cycles much smoother from the start instead of taking 10-20 mag loads. I used to have the whole family sitting watching TV with towels on the floor cycling ARs while we watching TV 3 days a week to keep caught up. So first thing is lets make sure you have same pattern upper and lower. Next check and see what drill bit shaft fits in the gas port. Inspect your bcg screws and staking. [/QUOTE]
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AR15/10 Rifles
AR10 cycling problem
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