10mm/.40 Magazine Feed Lip Spacing

[RevolverJockey]

My Limited will run fine for thousands of round, 700-1000 rds between cleanings then suddenly will start ejecting a live round with the spent brass and chamber the next round in the magazine. I will go several mags and lose a round or two from each. Then it will go back to normal, even though I changed nothing, and the problem is not limited to just one magazine. I will probably try adjusting them all the same and play around with oal and see if the problem is an early/uncontrolled release from the magazine coupled with wide feed lips. Can someone measure the feed lip spacing on a new/nearly new 10mm mag for me? If not, I am short of ideas. Thanks in advance.

Lee

[Sean.McCanne]

It does sound like your mag lips might be too wide. I generally adjust mine so that when almost full, I cannot pull the nose of a bullet up through the feed lips with just finger pressure. I'm not sure what the actual specs are on the mags, though. If I get a FTF I'll tighten them up a little until. As for OAL, I load mine to 1.195" currently and don't get FTF very often. I shoot a match indoors once a month (mostly), so sometimes I get to drop my mags on concrete. I'm sure that's not good for the mags, but hey, it's trigger time.

Hope that helps.

[CHA-LEE]

The inner width of the feed lips should be no wider than .385 inch. Otherwise you run into the issue you are facing.

[Sean.McCanne]

The inner width of the feed lips should be no wider than .385 inch. Otherwise you run into the issue you are facing.

Awesome! I hadn't found that. Thanks.

[RevolverJockey]

The inner width of the feed lips should be no wider than .385 inch. Otherwise you run into the issue you are facing.

I just miced mine, even the ones that are only about 2 months old (not having a problem) and they are about .401(2). Is there a preferred way to tune them?

Lee

[CHA-LEE]

Mitch_Rapp.45> I use a pair of needle nose pliers and push the feed lips inwards. DO NOT grip the feed lips themselves with the pliers. I grab it forward of the feed lips and straight down about an inch then basically bend the whole side of the mag body in. Since you really can't change the width of the back of the feed lips I mainly look for the .385 number at the front edge of the feed lips. So there will be a little bit of wider on the back and then narrower on the front taper to it. Warning though, ff you grab it by the feed lips and put score marks or ridges on them you will have a whole new set of problems on your hands.

A good way of testing the feed lip width at a match is to load the mag up fully and then with the top round fully seated pull straight upwards on it. It should hold its location firmly and you should not be able to pull the round upwards to slip past the feed lips without considerable effort. The angle of the case as the top round sits in the magazine should match the angle of the feed lips when you look at it from the side. If the case is pointing upwards more than the feed lips then they are too wide. If the case is pointing downwards more than the feed lips then they are too narrow. The key here is to test this angle when the magazine is completely full. That is when the most spring tension is placed on the rounds and the most force will be pushing the feed lips outwards.