Failure to feed problem (SOLVED)
I have installed a new Colt M4 barrel on my Colt A3 upper. It will not feed whatsoever. The round moves up the feed ramps and hangs on the locking lug about midway on the round itself (not the case). I read through the FAQ's and the only thing that I can see would be the barrel being more than .012" away from the mag well. And just in case someone asks, yes the barrel has M4 ramps, and no the receiver does not have ramps. The round is not hanging on the barrel extension. The round hangs on the locking lugs. If it is the barrel setback, what type of depth gauge would I need to check it and what is the accepted "standard procedure" for measuring the <.012"? Thanks for any and all help. I have built several rifles in the past, but this is a new problem for me. I hope it is something simple, but... I thought I would get some opinions.
If a pic helps, I can email them, but not post.
it does this live fire?
Actually, it hasn't fired yet. The round will not feed into the chamber whatsoever. It always hangs.
It would be nice to have a picture of this. I had an oly with a barrel cut with the M-4 profile and a non cut upper. The rounds would sometimes hang on the ramps themselves, usually not enough to stop the cartridge at that point but just enough to cause the bolt to not lock in place. When the cartridges were picked up from the magazine they were shoved into the feed ramps hard enough that they etched into the metal. I buffed it slightly and that seemed to fix that problem.
ETA: my email is email@example.com if youd like to send a pic
are you riding the charging handle?
whose mags? what ammo?
does the upper pass the 40 degree check?
I have used GI mags, Colt factory mags, DPMS, new, used, range, every brand and shape and I get the same failure.
I have tried Winchester Q3131A, PMC 55gr, Federal 55gr, Winchester white box 40 gr varmint. I haven't run any match ammo through it b/c it destroys the round when I try and feed it.
Not riding the charging handle. Pull to the rear and release (slingshot). The bolt hangs when the round moves into the feed ramps. I can pull the bolt back again a couple of times and eventually it will force the round through the ramps, but the round is in bad condition by then.
I am working on some high quality pics for you guys. My little camera will not get a good shot of the chamber. It might be a day or two.
Thanks for the input so far.
Passes the 40 degree test with flying colors. The bolt works just as smooth as can be.
I had the same problem with a few uppers I built. Had the lug area polished to remove the sharp edges, no problems since.
Does the bullet get wedged? Causing a "V" shape gouge in the bullet? If so, that's what my uppers were doing.
The bullet does get wedged and gets a "V" shape gouge. I looked at the lugs real close and it feels like there are two small edges curled up into the ramp. I will polish those out tomorrow and see how it goes from there. Thanks for the help everyone so far. I got to get this gun running and get it to the range!
I sent my uppers to Bushmaster after getting an RMA number due to the fact the barrels were NIB Bushmaster barrels. They removed a slight bit from the area and the rifles have not missed a lick since.
Nothing more frustrationg than a damn AR that won't run. Good luck.
Some of the new barrel extensions/ramps are very sharp, and some have the newer "double cut", I have encountered many that will grab and hold the bullet about halfway before the casemouth. It's always been an easy fix with a dremel and the right bit. Polish the hell out of the feedramps, if it still hangs then grind open just a TINY bit at a time (be very careful not to change the feed angle), do not grind the bottom of the ramps, just the upper portion until it feeds correctly. Then get some "cold blue", blacken it up and then oil it. It's really pretty easy if you go slow and test.
I dremeled the feed ramps until they are butter smooth this morning. The weapon cycled flawlessly by hand with no bullet or case markings. I am going to shoot it later this afternoon and see how things go in the real world. Thanks for all of your help, I have managed to keep at least some of my gray hair. I will post range results tonight.
Looks like I'm having the same problem with a stock Bushmaster; my bullets have the V mark on them and some mags won't feed at all. I guess I'll send it back to Bushmaster to have it touched up.
I bought a $10.00 polishing kit from Wal Bucket and in 5 minutes had mine running smooth. I did take the barrel out of the upper so that I could get to the ramps better. I doubt that you have to do that, I just wanted to take it all the way down anyway. I got some cold blue as suggested for $3.00 and it looks like a factory piece.
Range Report - shot like a champ, although it takes more windage at 25 than I would like. I am going to verify the sights tomorrow with a standard carry handle. I guess it's always something. As far as cycling and shooting, it couldn't function better. I really think Colt should offer a Dremel certification course.
Thanks again to all who contributed.
I don't have the tools or skill to take the upper apart, so I'll just send it in.