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Posted: 12/10/2014 1:29:46 AM EDT
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So, I'm having a problem getting my rounds to load from the magazine. WIth the bolt locked to the rear, I'll pop the magazine in and release the bolt. No problem loading. It jams up on cycling though. Once the first round ejects, the next round gets wedged between the bolt and the point between the upper and the barrel extension (indicated in the picture). At this point I have to clear it and start over. I've tried both Pmags and Battlemags using steel and brass. Same result.
The barrel extension does not extend past the feed ramps of the upper. In fact, there's a very very small landing on the upper ramp before it transitions to the barrel extension ramp. Is this normal, or should it be a smooth transition all the way up? Should I try to grind that ramp down? Any suggestions? TIA. 
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Could be anything from magazine lock up, to gas, to dirty chamber. Or more.
Could you please list the specs of the build and what you have done to troubleshoot so far? If it is a new build, I would start with a chamber brush and CLP or another good clean and lube product. |
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Quoted:
Could be anything from magazine lock up, to gas, to dirty chamber. Or more. Could you please list the specs of the build and what you have done to troubleshoot so far? If it is a new build, I would start with a chamber brush and CLP or another good clean and lube product. It's a Colt 6720 Barrel mated to a no name upper (m4 feed ramps). DPMS bolt assy, PSA buffer & LPK, Spikes lower... As far as troubleshooting, I've only run through different ammo with different mags. Seeing as how it replicated regardless of the combination, I've mostly ruled out it being an ammo/mag issue. There's no apparent ejection issue, either. |
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Quoted:
try pulling the charging handle all the way back and letting it go. trying to get the same force as letting the bolt go from the bolt release. (if you haven't already) also just to be safe: point in a safe direction when doing this if using live ammo I'll give it another shot. Being the third AR I've built and the first time I've seen this, I somewhat assumed it would be some sort of physical issue. I can't discount the possibility of an ID10T user error, though. I'll give it a good thorough cleaning and come crying back if I contine to have issues. |
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Barrel extended ramps do not match the extended upper receiver ramps (have a step protrusion).
Not grinding, but if you built the upper, pull the barrel and polish the bottom of the barrel ramp edges to align them correctly with the upper receiver ramps (400 wet/dry sand paper wrapped on a chopstick will work fine to just rework the very ends of the ramps to take them down a few hundred throusands of a inch to flush out with the ends of the upper receiver ramps ). If you bought the upper pre-built, then send it back to have it corrected instead. |
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Quoted:
Barrel extended ramps do not match the extended upper receiver ramps (have a step protrusion). Not grinding, but if you built the upper, pull the barrel and polish the bottom of the barrel ramp edges to align them correctly with the upper receiver ramps (400 wet/dry sand paper wrapped on a chopstick will work fine to just rework the very ends of the ramps to take them down a few hundred throusands of a inch to flush out with the ends of the upper receiver ramps ). If you bought the upper pre-built, then send it back to have it corrected instead. It's actually the other way around. It's like the barrel extension is just a hair too short to line up with the lower ramps. One would think that it wouldn't be an issue, but it jams up right there. |
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Round moves forward into the chamber on feeding, and you do not want a protruding edge/lip between the barrel and receiver ramps for the tip of the bullet to slam up against on the way forward during feeding up the ramps.
Simply, the ramps should flush to each other, or even the end of barrel feed ramps up against the receiver ramps slightly below the end of the receiver extension feed ramp edge is fine as well. Since you can not add metal to the upper receiver extended feed ramps, then it a matter of taking some metal off the corresponding ends of the barrel extension feed ramps to lower them to remove the protruding lips/edges instead (so the tip off the bullet does not slam into them). But lets back this up, and if you bought the upper built, then send it back to have the manufacturer resolve the problem instead. It could be the barrel extension, or ever the barrel extension that was produced out of spec for the two to mate up correctly, and one of them will need to be replaced. Hence, if you are going to rip Colt off for the M-4 extended ramps design, then at least get it right so the ramps between the barrel extension and receiver mate up with each correctly (and you don't have protruding edges in the ramps for the bullet tips to slam up against them). |
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Simply, the ramps should flush to each other, or even the end of barrel feed ramps up against the receiver ramps slightly below the end of the receiver extension feed ramp edge is fine as well. This is the case exactly. Just to clarify, the Barrel feed ramps do not protrude. If anything, they're recessed a hair from where the bottom of the barrel ramp meets the top of the reciever ramp. |
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Run a sharpened pencil up the the ramps at the same angle a round would feed and see if the tip of pencil is sheared/crack off from a protruding lip up the ramps.
Right now from the photo you show, looks like the ends of the barrel ramps are proud of the ends of the receiver ramps, and you have edge protrusions that would catch a bullet tip. |
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Run a sharpened pencil up the the ramps at the same angle a round would feed and see if the tip of pencil is sheared/crack off from a protruding lip up the ramps. Right now from the photo you show, looks like the ends of the barrel ramps are proud of the ends of the receiver ramps, and you have edge protrusions that would catch a bullet tip. Great idea! I'll try that too. I think it's a crappy angle + crappy picture. Thanks! |
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