View Full Version : Strange Ejection Issue
Hello All,
I have a new LMT MRP. Ive put 1000 rounds through it and its ran great. BUT, i documented six times where the last round of a magazine was fired, and i found the case loose in the chamber resting on top of the magazine follower. The bolt was locked back behind the catch. Three separate times I found the case turned around with the primer facing forward toward the barrel. Numerous other times i observed the last round of a mag BARELY make it out of the chamber. Note, the rifle has never double fed, stovepiped, or malfunctioned in any other way. This only happened six times on the final round of the magazine. All 1000 rounds were fed xm193.
I inspected the extractor, ejector, bolt face and everything seems to be to spec. However, upon inspecting the magazine followers (10rd pmags) I found pretty deep grooves where the bottom right bolt lug passes over. I think the follower and bolt lug are interacting in a negative way on the last round.
Initially, i thought it was a single mag causing the problem. But then it starting happening with both. Interestingly enough the scraping is significantly deeper on the mag that i first encountered the issue with. It almost seems like the lug is running into the top right part of the follower as there are grooves that have developed there.
I believe the action is cycling fine but the mag followers are fouling the action on the last round causing a somewhat off ejection. Ill test different brand mags next weekend but until then, any ideas?
Getting any of these follower signs on other type mags?
I think it's your mags. What brand of 10 rounders are you using?
They are 10rd gen3 pmags. I have to get my hands on another brand.
Are you limited to 10 rounders where you live?
Replace the extractor spring.
Try different magazines before taking the bolt assembly apart. Clean the chamber to make certain brass is not dragging on dirt or a rough spot. Also make sure the BCG assembly is cleaned and well lubed.
If that doesn't work, empty brass is being pulled clear of the chamber and winds up laying on top of the magazine follower, it could be an ejector issue. On more than one occasion, I have removed the ejector and spring from the bolt and found flashing inside the channel where the ejector travels. After cleaning and reassembly, brass was thrown clear of the weapons.
Are you limited to 10 rounders where you live?
Yes :(
The locking lugs on the bolt shouldn't be touching the magazine at all. Have you slowly hand cycled the BCG while watching what's going on through the ejection port?
The locking lugs on the bolt shouldn't be touching the magazine at all. Have you slowly hand cycled the BCG while watching what's going on through the ejection port?
Yes I have. the bottom right lug scrapes the follower. The lug does not however scrape rounds on a loaded magazine. The bcg glides right over them.
I have some 10 rd Pmags and some 10 rd Lancers. I'll try them later today, doing the hand cycle thing, and see what's going on with my AR's.
The locking lugs on the bolt shouldn't be touching the magazine at all. Have you slowly hand cycled the BCG while watching what's going on through the ejection port?
The lug does indeed contact the magazine follower when the magazine is empty. This problem is not caused by the magazine. The magazine cannot come in contact with the extracted case unless the extractor lose control of the case
Yes I have. the bottom right lug scrapes the follower. The lug does not however scrape rounds on a loaded magazine. The bcg glides right over them.
Inspect the lug for damage or a burr or something. It shouldn't be cutting a groove in your follower.
The lug does indeed contact the magazine follower when the magazine is empty. This problem is not caused by the magazine. The magazine cannot come in contact with the extracted case unless the extractor lose control of the case
Inspect the lug for damage or a burr or something. It shouldn't be cutting a groove in your follower.
The lug isnt chipped,burred, or even worn more than the others. Theres no evidence of anything abnormal happening around the barrel extension either.
Im going to have to say its the followers as the only time this happens is when the follower comes into play. If it was something else, I would be getting malfunctions throughout the magazine.
There's a theory that has been floated around the 'nets for a while that 10 round mags have more spring pressure when empty vs. a 30 round mag. This would force the follower up into the BCG with more pressure than a 30rd mag. Not sure if it's true, but it would certainly be measurable.
Yeah, Mistwolf is right, one lug touches the faux cartridge on the follower. Is the gouge in this area, or somewhere else? And it's only on the last cartridge it happens on? Is this right? Reread your OP....last round only.
Yeah, Mistwolf is right, one lug touches the faux cartridge on the follower. Is the gouge in this area, or somewhere else? And it's only on the last cartridge it happens on? Is this right? Reread your OP....last round only.
Correct on everything
Check the backside of the lug. The only time the lug will contact the follower is during the extraction of the last round. If the follower is dragging enough to slow the BCG to leave the empty in the action, there is a two-fold problem. First is obvious- the dragging which causes the gouging. Second, the extractor is losing control of the case. Even with the dragging, the extractor should hold the rim of the case until it can be ejected, especially if the BCG locks back.
Got a different bolt or BCG you could try?
Ok so I got a tangodown magazine. the follower has the faux cartridge on the left side. the left lug contacts it, but on its flat surface, not on the sharp corner. Also it contacts it much later in its rearward travel. Furthermore, it locks up in the magwell much differently. ill report back after I test it later this week.
just got off phone with LMT. They have experience with 10rd magazines causing all kinds of issues. according to the tech, who was VERY helpful, the tolerances of my specific build and the tolerance of this lot of 10rd pmags probably just doesnt line up for 100% reliability. Bolt/bcg +mag follower friction can induce problems like Im having. He also said hes personally seen where a low velocity ejection will bounce brass off the reflector and back into the ejection port.
LMT guy: "are you using 10 rounders because youre in california?"
Me: "yes"
LMT guy: "ahhhhh im sorry about that"
EzGoingKev
11-06-17, 14:58
I have two Magpul 10 round magazines that I use at the range all the time. They have worked 100%, no issues at all.
Ok so I got a tangodown magazine. the follower has the faux cartridge on the left side. the left lug contacts it, but on its flat surface, not on the sharp corner. Also it contacts it much later in its rearward travel. Furthermore, it locks up in the magwell much differently. ill report back after I test it later this week.
just got off phone with LMT. They have experience with 10rd magazines causing all kinds of issues. according to the tech, who was VERY helpful, the tolerances of my specific build and the tolerance of this lot of 10rd pmags probably just doesnt line up for 100% reliability. Bolt/bcg +mag follower friction can induce problems like Im having. He also said hes personally seen where a low velocity ejection will bounce brass off the reflector and back into the ejection port.
LMT guy: "are you using 10 rounders because youre in california?"
Me: "yes"
LMT guy: "ahhhhh im sorry about that"
Another poor guy like me. That's a very odd combination of "things" that conspired against you. I do use hi-caps, but I also use 10 rd PMAGS, 10 rd Lancers, and 10 rd Hexmags. All have worked well in my AR's. Maybe try the last 2 plus your Tango, if they work, use the PMAGS for something else.
well i couldnt resist so i went to the range. 120 rds with the tango and no problems.
I'll be interested to see how this fairly new rifle does with another 2000-3000 rounds through it. The newest glock I bought worked well for 400rds then malfunctioned left and right for another +200rds before smoothening out. Its my carry gun at work now.
ok boys,
so i have deducted that I have a slightly overgassed system. the weird ejection problem has ceased since switching mag brands. furthermore, i do not experience strange ehect patterns when i use other ammo brands. the specific lot of fed xm193 that my lgs carries might be a hot run + the tight tolerances of the rifle creating some of the intermittent problems i was having.
long story short, nothing was wrong. I was gripping the magwell(touching the mag) on a tight tolerance gun using pretty hot ammo.
750 rds later using different mags, not holding gun by magwell, using same ammo= no problem.
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