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Posted: 4/5/2009 10:19:34 AM EDT
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I picked up an upper a few months ago and finally got a chance to take it out to the range the other day. Nearly every shot, it was having a failure to feed. When I loaded the first round with the charging handle, probably 95% of the time it jammed. Even on the few times when I got the first round to feed correctly, the 2nd round jammed nearly 100% of the time. I tried different mags and different types of ammo and each time it was the same. I also tried a different bolt. All of the mags and both bolts I tried work perfectly on my other AR. On a number of the rounds, when I dropped the mag and cleared the jam, the bullet was scratched pretty deeply and pushed into the casing. I was able to recreate the problem with snap caps and pics are below. I also took a few pics of the empty chamber if that helps. Please let me if know if yall need any other info to help diagnose the problem. Thanks in advance.
Dan 
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I tried it on another lower (I have 1 other AR, a S&W) and it had the same problems. I was hoping to have a dedicated lower, a CMMG lower that I built. As a test, I used the CMMG lower with the S&W upper and didn't have the problem.
I will try adjusting the mag catch. Would I need to tighten or loosen it? Thanks for the reply QUIB. ETA: When I look closer, its almost like the tip of the bullet is getting wedged in the feedramps. |
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Quoted:
I will try adjusting the mag catch. Would I need to tighten or loosen it? If you tried the upper on other lowers that function with their uppers, and the problem still exists, then it’s most likely not a mag catch issue. But, if you want to try adjusting the mag catch a good basis to start from, would be to adjust the catch so that the threaded portion of the catch is flush to just under flush with the top of the mag catch button. |
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i actually just finished adjusting the mag catch (I loosened it). It significantly reduced the number of jams. I only have 4 snap caps but in loading and reloading them 3 times I only had 2 jams, and pulling the charging handle back again fixed the problem (whereas it didn't fix it before). Hopefully I will be able to get to the range in the next week or so to try it out to see if it fixed the problem. I really appreciate the help.
Dan |
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Good deal.
Take her back out, and run some rds through her. If necessary, loosen the catch and try again. When the mag catch is too tight it keeps the magazine from floating and self adjusting as rds are stripped and loaded. The mag is held at one angle and sends the rds into the barrel extension rather than the feed ramp. Loosening the catch allows the mag to float as the rds are stripped, letting them glide along the feed ramps and into the chamber. |
| I put together a complete AR not too long ago. When I first tried shooting it, evey round would short stroke. It would fire, eject the round but not completely retract far enough to catch the next round. Many times when it did catch a round and try to feed, the round would not go all the way in. It would stop kind of like in the picture you show. I figured out it was just tight tolerances and no break in. I lubed the hell out of it, cycled it about 200 times by hand and then put another 200 rounds though it. But the end of the first 100 rounds, the problem went away and it began to function more reliably. Since then, I have shot about 400 more rounds and have not have a single jam or failure to feed yet. In my case it just needed to be broke in. It was all real stiff when I first assembled the rifle. Could it be that your rifle just needs to be broken in? Lube the hell out of it ...... I mean dripping and see what happens. |
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Quoted:
I put together a complete AR not too long ago. When I first tried shooting it, evey round would short stroke. It would fire, eject the round but not completely retract far enough to catch the next round. Many times when it did catch a round and try to feed, the round would not go all the way in. It would stop kind of like in the picture you show. I figured out it was just tight tolerances and no break in. I lubed the hell out of it, cycled it about 200 times by hand and then put another 200 rounds though it. But the end of the first 100 rounds, the problem went away and it began to function more reliably. Since then, I have shot about 400 more rounds and have not have a single jam or failure to feed yet. In my case it just needed to be broke in. It was all real stiff when I first assembled the rifle. Could it be that your rifle just needs to be broken in? Lube the hell out of it ...... I mean dripping and see what happens. His problem is a bit different than yours. His rounds are stripping fine, but hitting the feed ramps. Nothing that lube can help, as in your case. Adjusting the mag catch has obviously helped enormously to this point. Now all that is required is to live fire the weapon and possibly make a few more adjustments. |
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Quoted:
Quoted:
I put together a complete AR not too long ago. When I first tried shooting it, evey round would short stroke. It would fire, eject the round but not completely retract far enough to catch the next round. Many times when it did catch a round and try to feed, the round would not go all the way in. It would stop kind of like in the picture you show. I figured out it was just tight tolerances and no break in. I lubed the hell out of it, cycled it about 200 times by hand and then put another 200 rounds though it. But the end of the first 100 rounds, the problem went away and it began to function more reliably. Since then, I have shot about 400 more rounds and have not have a single jam or failure to feed yet. In my case it just needed to be broke in. It was all real stiff when I first assembled the rifle. Could it be that your rifle just needs to be broken in? Lube the hell out of it ...... I mean dripping and see what happens. His problem is a bit different than yours. His rounds are stripping fine, but hitting the feed ramps. Nothing that lube can help, as in your case. Adjusting the mag catch has obviously helped enormously to this point. Now all that is required is to live fire the weapon and possibly make a few more adjustments. I see now.......guess I read it wrong. Learned something though (about the mag catch) |
| Look at the barrel extension the feed ramps look like they are not deep enough even by a standard extensions standards.Those ramps should at least meet the uppers ledge.Are the rounds hiiting the ramps edge causing FTFs?You can see under the left ramp some brass copper strikes from the bullets nose..at least thats what it looks like to me.As L lokka ta it again something just doesnt look right on that barrel extension.You buy the upper new or used?and was it factory assembled or individual install?Ive seen that where the barrel nuts been overtightend and the index pin damaged causing barrel movement and slight mis alignment causing that type of malfunction.If the mag catch loosening doesnt clear up the problem 100% id have some one take the barrel off and ss if anythings going on there. |
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