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Mag Fed Shotguns and Rim Lock?


ropsitos

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Started some limited testing of my new MKA1919 mags from T&N, and 18 and a 10.  Gun is a match version.

Cycling dummies I would occasionally get what looked like a double feed.  Decided that wasn't especially telling so I took it to the range,

First run through both mags ran flawless.  Big smile.

2nd run after a reload to the the 10 rounder, somewhere in the middle of the mag, jams up with what, at the time, looked like a double feed.  Drop mag, clear, move on.  Still big smile.

3rd run the 18 does similar, near the end of that mag, right before I reloaded.  10rdr ran fine.  Big smile remains.

Watching the video, that I happened to set up, the spent shell ejects, and the next shell loading doesn't make it into the chamber.  I did not pay close attention as to how it jammed up (which I should have 'cause that might have answered my questions).

Wondering if when loading the mag, I rim locked a pair of shells, or if it's possible that a pair rim locked themselves in the mag during shooting?  I was careful in loading, to avoid such a thing, but not absurdly so (because I was having a stupid amount of fun).

What does a rim lock jam look like?  Does the fed shell make it to the chamber opening or does everything stop with the bolt farther back?

Shooting walmart 100rd box federals, 7-1/2.  Other than the two jams out of 75 rds or so, it ran great.

Further investigation required on my part, both hand cycling and live fire, but I wanted to hear opinions on the rim lock theory.

thanks
Bob

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I had this problem when I first started loading my T & N  MKA mags. You have to be careful when you load not to overlap the top shell and lock the rim. Tooth & Nail has a video here somewhere on a good technique to load the mags. Keeps rim lock to a minimum. When you get a rim lock, the mag will not feed at all. Stops completely. Top shell goes over and behind the next one down instead of in front of the rim. I have found that if you pull the mag and hit it hard on the bottom it will pop the top round either out or fix  it and you can re-insert it. You can bang it with your hand or on the ground. Never had it lock while shooting always from loading. I have found that if I only use Win AA 1145fps I eliminate most double feeds and problems. I had a lot of problems with the less expensive shells. Not consistent in power or diameter.

Double feed is not a rim lock, probably not enough to cycle the bolt completely. Try better higher FPS shells. What spring are you running? Mine came with a heavy spring and after shooting about 500 rounds of good higher power (1250-1300fps AA) rounds to break in I changed to the lighter spring and the gun runs great with the lighter 1145 AA loads. Get with Matt or Josh at T&N for help. My gun runs amazing 99% with all mags from 5-10-15-18-24.  Shoots Wolf or Extreme Slugs like a laser. Does not like Fiocchi low recoil slugs ends up with double feeds.

gerritm

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With a rim lock the bolt will stop towards the rear. The top rim has slipped behind the second shell in the mag preventing it from chambering. Quick way to override a rim lock on the clock is to slap the back of the charging handle. Gerrit is correct in double feed and rim lock are two separate issues. Federal Bulk seems to have gone further into the territory of Winchester Universal and SuperX. Neither of which I recommend for any gun. Detailed information about what the rounds look like when having "jams" is the key to getting everything tuned correctly.

 

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1 hour ago, LoganbillJ said:

Quick way to override a rim lock on the clock is to slap the back of the charging handle. 

I would have never guessed that would work.  I just need to remember that the next time it happens.

The OP also asked if two shells can move into a lip lock position from shooting the gun?  I try to take my time loading magazines but  on the rare occasion it has jumped up and bit me at the most inappropriate times.

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5 hours ago, gerritm said:

What spring are you running?

Stock spring that comes with the match version.  I'm not even sure I would say it's completely broken in yet.  Tough to do with only 5 round mags.  Those things are "fun blockers".

this is the malfunction I caught on video.  Around the 20sec mark.  From your descriptions it doesn't sound like rim lock.

 

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My Vepr wouldn't cycle the Federals reliably either. From what I could figure out the hull flexed too much in the mag. It would essentially "squish" out of round causing it to stop part way to the chamber. Switched to Winchester AA and the problem disappeared almost entirely. The box mag-fed guns tend to need a stiffer hull.

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I was instructed by Matt & Josh to run at least 250-500 rounds of higher power shells. 1250-1350- FPS. Not sure what spring is in there to start, but mine had a stiffer one and then I changed it to the softer one. The harder smooth shell on AA's seems to stay consistent with feeding.

Being in open the gun is only as good as the mags and the rounds you feed it. I have seen the cheaper shells come out the box especially as hot as it gets here in Texas egg shaped and out of round. They work OK in pumps and most semi's. Eliminate your chances of failure.

Video looks like it didn't completely cycle. Run better heavier power shells. Spray the arms and guide rod lightly before each match. Likes some oil. I use Royal Purple syn. spray gun oil.

gerritm

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8 hours ago, PatriotMRD said:

My Vepr wouldn't cycle the Federals reliably either. From what I could figure out the hull flexed too much in the mag. It would essentially "squish" out of round causing it to stop part way to the chamber. Switched to Winchester AA and the problem disappeared almost entirely. The box mag-fed guns tend to need a stiffer hull.

Stiffer hulls help in all mag fed shotguns. It really helpd feeding and stops the nose of the hull from deforming when it hits the feed ramp too. My Vepr12 runs great on AA shells, but as added security I keep my hulls in a cooler on the range to keep them from getting to warm as the heat makes hulls softer. This trick has nearly eliminated malfunctions in my OPEN shotgun.

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Based on your video it looks like a double feed. You removed the first round of the double feed, charged it again which caused another double feed. Look at your feed lips and the relationship between the front and back of them. The rear(where the rim rests) needs to be wider than the front(about 1/2" forward from the rear). I recommend at least .01" but each gun is different and actual measurement will vary from gun to gun.

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Does your cheek sting win you shoot? Your head  is not down on the gun. IT is slapping your cheek. It also appears to not be firm against your shoulder. Just a guess but short stroking causing a miss feed. IE limp wrist version with a shotgun. 

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11 hours ago, AHI said:

Does your cheek sting win you shoot? Your head  is not down on the gun. IT is slapping your cheek. It also appears to not be firm against your shoulder. Just a guess but short stroking causing a miss feed. IE limp wrist version with a shotgun. 

Not usually, but I have gotten smacked by my own hand shooting my beretta when choking up on it more than usual.  I've never had an issue with the beretta.

That said, I wondered the same thing, i.e., limp shouldering, because of how horrible my form looked overall on the video.  First time I've videoed where it wasn't in the first person.  I was just watching that beretta video with that Roberto guy on form, and made me think similar things.

I think I've got some things to try out and I think I've got a solid answer that what I experienced was not rim lock, so I don't have to pay any extra attention to that and can focus elsewhere.

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Check the height of your red dot....seems like you are taking a lot of recoil especially when you shot at a higher target....when we fit a shotgun to a new customer ...making sure it is unloaded and bolt locked to the rear... look down the sights from the muzzle end of the barrel and determine where they line up to your eye....you can tell a lot about the fit and highth of the comb that way.

 

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  • 1 year later...

Yes, rimlock will occur from shooting.

I have never had an issue while actually shooting, but, if I have a partially loaded magazine, that I just used, I unload it, and usually find some shells in it that have jumped over the top of each other, probably due to recoil.

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