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Feed lip adjustment on mags.


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What exactly are you guys doing to the feed lips to get the shell to present a little higher?  I seem to have an issue with the second to last round on at least 2 different mags.  Seems like that second to last round has just the right lack of pressure to get it to feed right and it gets jammed upward at a 45 degree angle and doesn't feed.  It's just hard to replicate without shooting the gun.

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Best way to check this is insert a rd into the mag, preferably a dummy rd. Insert mag into gun. Pull the bolt to the rear and slowly let it down until it contacts the rear of the shell. There is a small tang that hangs down from the bolt. You want the rim of the shell to contact the bolt halfway up or higher. Continue to tweak the rear of the feed lips outward until the shell sits at the desired height. Be sure and look at the relationship between the distance of the front of the feed lips to the distance of the rear of the feed lips before starting. If the fronts do not travel out with the rear you will have problems with the bolt closing and going into battery due to the stiffness of stripping off a rd. This is especially true for those running a low power recoil spring. Hope this helps. Let me know if you have any further issues. Contact me if you have any questions while tuning. Thanks

 

 

Joshua Loganbill

573-378-9070

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Tuned them some.  Not that I could ever get a malfunction to happen while I was not on the clock......

 

One thing I noticed was that the top of the notch for the bolt catch was catching the lip on the shells as they rose.  So I smoothed it out a bit.  

 

Let's see what happens.

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Experimented with it some.  Shells seem more apt to flip up when the mag is not in the gun.  Like from being bumped around on my belt.  I also got 3 rounds out of 100 that angled up hard while loading into the breach.  The front of the shell was far enough int he breach, the back of the shell was out of the feed lips but being pushed up by the next round in the mag.  It was putting enough force on the round that it was really hard to clear.  I had to hold the bolt back, push the mag release, and pull the mag down pretty hard to get it and the shell out.  The nose of the shell that jammed was bent about 3/4" from the front where it was being bent over the feed ramp.

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Tightening up the front of the feed lips will solve the issues of the shells being bumped out while on your belt. Be sure you are tightening the front of the feed lips not the wings that cradle the front 2/3 of the shell.

 

Most nose up jams are difficult to clear without dropping the mag. Nose up jams are caused by the shell not being presented high enough. The friction from the bolt actually strips the rd from the magazine. This causes the rd to be stripped while the bolt is already halfway up the rd. The rd hits the feed ramp and begins traveling upwards while the bolt closes on the nose of the rd forcing the rear of the shell downward. Open the rear of the feed lips up a little more so the shell is presented higher as I stated above.

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IMG_0015_zps95ba904a.jpg

This is about as high as I can get it to sit.

I did this and the bolt hit stuff and would not go forward.  Nor would it really hold the round in.

IMG_0007_zpsd020f61e.jpg

 

I could not get it to jam with dummy rounds.  Maybe the Fed and Rem rounds are a little softer sided and let the nose bend and not help it lift the back.

 

Other pics of how it is and seems to work.  2 jams out of like 100.

IMG_0020_zpsfc0bb5af.jpg

IMG_0018_zps5401448f.jpg

IMG_0016_zps838ec02c.jpg

IMG_0021_zpsa2ecd44b.jpg

IMG_0022_zpsf9c96dc7.jpg

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When the shells can rotate up like that you need to tighten the front of the feed lips just a little. That should cradle the shell just enough to prevent the rotation you are getting in the last 2 pictures. Are you still getting the nose up jams? Where is the rim of the shell contacting the tang on the bolt?

 

Videos can be made but most of the tuning aspect is tough to explain and show, as the adjustments made are very minor. I tune all the mag for the guns we build but I do it all on feel anymore. How the shells load, how it feels when you manually strip the rd from the mag. As long as your shells are being presented high enough to engage the tang on the bolt correctly the rest of the reliability comes from the ratio of the distance between the rear of the feed lips and the front of the feed lips. Obviously you want the feed lips to be straight with no hard curves in them but they do need to be angled in slightly.

 

I use a set of alligator needle nose pliers. They allow you to manipulate the feed lips well without putting any curves or bends where you one need them. I have used regular needle nose before and the also work well.

 

 

Joshua Loganbill

573-378-9070

 

ETA: Measured a set of mags that I just tuned for a gun. These were tuned specifically for the gun being built. Gun ran 100% after mag tuning. Zero failure to feed, zero failure to eject. 100% lock-back on last rd.  The ratio does seem to stay about the same between our builds though.

 

Mag #1

Rear of the feed lips: .715"

Front of the feed lips: .699"

 

Mag #2

Rear of the feed lips: .720"

Front of feed lips: .700"

Edited by toothandnail
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Duct tape and Styrofoam work great if you need a coupler in a pinch or if you want to try it out before buying.

 

Got the following pictures of the mags I mentioned earlier. Again, these mags were tuned for the gun being built. Your rds may need to sit higher or lower in the mag depending on your gun or mags. The polymer over-mold process is not very accurate in the placement of the steel mag body thus creating differences between mags and measurements.

 

Mag 1

post-43678-0-30471200-1386964893_thumb.jpg

post-43678-0-57110500-1386964948_thumb.jpg

post-43678-0-11547200-1386964921_thumb.jpg

 

Mag 2

post-43678-0-24652800-1386964966_thumb.jpg

post-43678-0-67493200-1386965041_thumb.jpg

post-43678-0-95310700-1386965012_thumb.jpg

 

Joshua Loganbill

57-378-9070

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This helped a lot.  Those pics really put it into perspective for how much/little they need to be tweaked.....I was pulling them out waaaaaay too far.


I get that every gun is going to be a little different as well......but man.....I was getting the round up way too high and way too loose.

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I measured some of mine and think I might have gone too far.

 

1.  .77 rear .76 front

2.  .79 rear .80 front

3.  .77 rear .75 front  I think this one jammed on the 2nd to last round once

4.  .75 rear .80 front  I know this one jammed on the 2nd to last round and the last round once.

 

All of these jams were the kind where the nose went into the breech about a half inch and then the bolt slammed shut on the round.  All of these were with Remington #8 shot sporting clay loads.

 

I think I'm going to take them all back in just a hair.  I have them labeled now and I'll keep better track of which ones I know fed wrong.

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Everyone's measurements will be slightly different. If you have a firebird lower they may be closer or wider depending on how they spec'd out their lower.

 

Labeling your mags is a good thing to do for competition for the same reasons. If you have trouble on one stage with a mag, you know you need to stay away from that mag until you have a chance to resolve the issue.

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I just feel like i went from one or two stove pipes to one or nose up jams per 100 rounds.  The stove pipes were easier to clear.

i have my pistol mags marked out already that I use in comps.  I kept taping and untaping and cleaning these mags and my marks kept wiping away.  I really need to etch them somewhere on the plate, follower, and body so when I break them down for cleaning I can do it more like an assembly line.

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Best way to check this is insert a rd into the mag, preferably a dummy rd. Insert mag into gun. Pull the bolt to the rear and slowly let it down until it contacts the rear of the shell. There is a small tang that hangs down from the bolt. You want the rim of the shell to contact the bolt halfway up or higher. Continue to tweak the rear of the feed lips outward until the shell sits at the desired height. Be sure and look at the relationship between the distance of the front of the feed lips to the distance of the rear of the feed lips before starting. If the fronts do not travel out with the rear you will have problems with the bolt closing and going into battery due to the stiffness of stripping off a rd. This is especially true for those running a low power recoil spring. Hope this helps. Let me know if you have any further issues. Contact me if you have any questions while tuning. Thanks

 

 

Joshua Loganbill

573-378-9070

 

Joshua, what do you mean with the fronts traveling out with the rear. I have this issue with not going into battery

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