View Full Version : Failure to feed malf; only when loading
I have an oddball malf with one carbine. I am trying to isolate the problem. Here's the hardware:
BCM midlength 16" ltwt upper
Semi-auto BCG (either LMT or Denny's)
Op spring in is spec, fewer than 1000 rounds
H buffer
Colt carbine lower (with sear block); I installed the carbine RE
Federal M193 cartridges
USGI mags that have fit and functioned with other carbine setups
Lube is Mobile One 10-30
Sometimes during testing the BCG will go forward quickly, other times it seems sluggish. No apparent rhyme or reason to it. I have pulled the spring out and checked for problems, measured it, and it seems fine.
Malf only happens on loading from a partially full magazine. Never has happened when shooting, only loading. In this case, cartridge will be pushed about 1" forward, then stop. (Have not noted if it is in contact with feed ramps.) Usually happens during the middle of a shooting session, when I put the carbine down for 10 minutes or so, then try to resume shooting. Outside temperature is about 35-40 degrees.
In my mind it could be:
BCG (although it ran well on a different lower)
Spring
Sear block (yeah, I know, it's on my list of things to get rid of)
Lube in cold temperatures
To isolate the problem, I am considering running the upper on a different lower, running the upper on a different lower (but, using the same spring and buffer as with the malfs), changing the spring, changing lube, changing BCG. Any ideas? :confused:
New mags?
Good point. All are USGI mags that have fit and functioned with other carbine setups. Please note that the malf only occur in the "middle" of the mag (with 15-20 cartridges inserted).
But, the BCG forward travel sometimes appear slow (i.e., not as "snappy" as with other carbines) even without a mag, during testing.
I'll include this above.
Belmont31R
12-20-11, 16:52
Could be a number of things.
-Lube is becoming a little tacky in the cold weather.
-Too much tension on the top round in the mags.
-First round is catching on something.
-BCG could be rubbing a lot on the hammer (make sure FCG is installed correctly).
-Action spring could be weak.
-Check the round that gets stuck for a lot of rubbing. A few scratches can be normal but look for gauges or lips on the feed ramp.
-Geometry on something could be off. Good idea to swap lowers/uppers with another gun that works and see if the problem could be isolated to one or the other.
-Try a different brand of mag. Not all USGI are created equal and every manf has problems from time to time.
Could be other things but thats what comes to mind. This is the first round like inserting a fresh mag and either releasing the BCG with the CH or bolt catch right?
Could be a number of things.
Could be other things but thats what comes to mind. This is the first round like inserting a fresh mag and either releasing the BCG with the CH or bolt catch right?
These are not "fresh" mags. This has only happened when I cleared the carbine and stopped shooting for 10 minutes or so. Then reinserted the mag I had been using. I have attempted loading by both locking the BCG back, and, by locking the mag and then pulling on the CH. I have swapped CHs (to a known "good" CH), in case the CH was bent and dragging, but the problem persisted.
At first I thought is was the lube, but this problem did not happen with other carbines using the same lube, which I also fired, then let rest, and started again. (The delay was caused when I changed positions on the line and dragged all my stuff to a longer range.)
This has happened with the carbine twice in two days. In between, I cleaned it and checked everything I could think of. The only real obvious hardware difference is that I switched lowers. But, that was between two that worked well.
Was it the same individual magazine both times? I feel like a numbskull typing this but I read the thread twice and saw no mention of that. Mags are the easiest part of the system to isolate.
I have attempted loading by both locking the BCG back, and, by locking the mag and then pulling on the CH.
I am confused by this statement. Do you mean you have tried chambering a round by releasing the bolt with the CH, and by releasing the bolt with the bolt release button?
I'd eliminate the lube concern quickly and easily by cleaning the Mobil 1 out and hosing it down with something lighter, like CLP (just for troubleshooting the issue).
Was it the same individual magazine both times? I feel like a numbskull typing this but I read the thread twice and saw no mention of that. Mags are the easiest part of the system to isolate.
Three magazines. This happens only when I stop shooting for a while, then restart.
It does not happen during shooting, only when loading.
I have not yet had an opportunity to retry the mags that failed. I will try that tomorrow.
I am confused by this statement. Do you mean you have tried chambering a round by releasing the bolt with the CH, and by releasing the bolt with the bolt release button?
Yes. Both methods.
I think I will scrub the lube and put in a new spring for good measure.
I am wondering if I should use a standard carbine spring or a Wolff extra-power. I don't use the extra-power springs, but I have a new one lying around.
I am wondering if I should use a standard carbine spring or a Wolff extra-power. Do not use a Wolff XP spring. This is just adding another variable into the mix. Use a new USGI type.
Do not use a Wolff XP spring. This is just adding another variable into the mix. Use a new USGI type.
You are absolutely right. Bad judgment on my part, and a measure of my frustration after two days of this crap.
I think the best way to test this is to swap springs with another lower of similar type (but without the sear block) and try shooting both of them with mags that failed. See if I can recreate the malf in either.
I'll bring along a new spring if the spring from the original lower seems to be the culprit.
.
Just a guess...
Since you are interrupting firing a mag, you have manually lock the BCG back. You may not be pulling the CH far enough to the rear and the Bolt Catch could be catching on the Bolt Carrier body and not on the Bolt face.
When you insert a new mag, the Bolt is not behind the next round in the mag but on top of it? Friction of the Bolt or the BC Body could be dragging the top round out of the mag but since the Bolt is not behind the round, it can't make it to the chamber.
Do the rounds that fail to load have scratches/gouges on them from the Bolt or BCG?
Do you see any wear spots in the RE that could hinder the BCG from going 100% rearward?
Just a guess...
.
I've checked the mags out in other carbine systems, without a hitch. I'll be working on the springs later this week.
nineteenkilo
12-27-11, 10:09
.
Do the rounds that fail to load have scratches/gouges on them from the Bolt or BCG?
I diagnose the majority of firearm issues I see using this method. The brass can tell you a ton about the action of a weapon. Take a look some time. You'll be surprised by the amount of preemptive action you can take as parts begin to fail from wear.
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.