How much should I take off the mag catch hole on GI mags?

[MisterB]

I have a newer AO M1. Interestingly, the mag the gun came with had not been modified, but yet the mag catch is the newer style AO that only accepts mags that have had the hole rounded further up on the top. I did this until the mag would stay inserted, loaded up some snap caps and attempted to feed a round. They kept jamming on the feed ramp just in front of the barrel. I continued to take more off the mag until I could reliably chamber a round. I haven't yet fired live rounds in this gun. I wanted to ask how much I should be taking off the hole on each mag? I didn't take much, but I've seen pictures of some that really are key holed out.

 

Didn't want to run in to problems when I take it to the range for the first time

[06AngusSG]

The standard amount is 1/10 of an inch since that is how much shorter the receiver is. But your gun might run better with a different amount. I start out taking it just enough to get the mag to stay and hand file it in The field till it runs good.

[anticus]

It's better to modify the mag catch and leave the mags as is. The magazines will hold their value as GI issue if they are unaltered.

[MisterB]

The standard amount is 1/10 of an inch since that is how much shorter the receiver is. But your gun might run better with a different amount. I start out taking it just enough to get the mag to stay and hand file it in The field till it runs good.

Thanks for the info

[MisterB]

It's better to modify the mag catch and leave the mags as is. The magazines will hold their value as GI issue if they are unaltered.

How do I do that? Wouldn't it require that I get a GI mag catch?

[ghostsoldier]

 

It's better to modify the mag catch and leave the mags as is. The magazines will hold their value as GI issue if they are unaltered.

How do I do that? Wouldn't it require that I get a GI mag catch?

 

Do a search here for my posts on modifying the stock mag catch, Mr.B...I uploaded a tutorial here several years ago, and it should still be around.

 

Rob

Edited August 15, 2016 by ghostsoldier

[brassmagnet]

One thing I ran into is amounts vary by gun. I did a bunch of mags for my TM1, and when I went to use them in my WH 1928 [semi] they were not opened up enough. Worked fine in the other gun though. I have enough mags for both, so I keep 20 rounders for the TM1 and the bigger ones for the '28. I think [in hindsight] changing the mag catch would be a better option also.

[papercutninja]

You can't just eyeball or measure it. Each mag will need a different amount. File/dremel little by little until they fit in there snugly. Don't overdo it. Also, don't let the snap caps be your measurement of functionality; my A-Zoom red anodized snap caps jammed EVERY time, but the gun shoots just fine.

[MisterB]

 

 

It's better to modify the mag catch and leave the mags as is. The magazines will hold their value as GI issue if they are unaltered.

How do I do that? Wouldn't it require that I get a GI mag catch?

 

Do a search here for my posts on modifying the stock mag catch, Mr.B...I uploaded a tutorial here several years ago, and it should still be around.

 

Rob

Thanks. I found them, but it looks like some of the images are missing from your image sharing service, and the links to the WWII reenacting site with more info that you provided don't work anymore.

 

I still kinda get the idea, but I'm torn as to which direction to head. At this point, out of the 5 GI mags I have, one of them has already been modified, and would become useless to me if I changed the catch

[MisterB]

You can't just eyeball or measure it. Each mag will need a different amount. File/dremel little by little until they fit in there snugly. Don't overdo it. Also, don't let the snap caps be your measurement of functionality; my A-Zoom red anodized snap caps jammed EVERY time, but the gun shoots just fine.

That's good to know. It sort of made me nervous when I saw those same snap caps get jammed

[ron_brock]

You can always sell the modified mag to others who won't take the time to mod the catch. I usually get the same or a little more when I get some. I'd go the mag catch route as well. Then you can shoot XX or XXX mags.

 

Ron

[anticus]

Tommygunner.com sells a mag catch already modified. I think they're asking $60.

[ghostsoldier]

 

 

 

It's better to modify the mag catch and leave the mags as is. The magazines will hold their value as GI issue if they are unaltered.

How do I do that? Wouldn't it require that I get a GI mag catch?

 

Do a search here for my posts on modifying the stock mag catch, Mr.B...I uploaded a tutorial here several years ago, and it should still be around.

 

Rob

Thanks. I found them, but it looks like some of the images are missing from your image sharing service, and the links to the WWII reenacting site with more info that you provided don't work anymore.

 

I still kinda get the idea, but I'm torn as to which direction to head. At this point, out of the 5 GI mags I have, one of them has already been modified, and would become useless to me if I changed the catch

 

Yeah, Photobucket dumped on it's users earlier this year, and broke all the links; here's a new link to my album, where you can get a pretty good idea of how it works: http://smg.photobucket.com/user/ghostsoldier/library/My%20Impression%20stuff/My%20Weapons

 

Rob

[papercutninja]

Ultimately, it's up to you whether or not you want to modify the mags. A lot of the guys here are hardcore collectors, and would hate to see a piece of history modified permanently. Having said that, TSMG mags are fairly common; every gun show I've ever gone to has had a couple of vendors with dozens of them. They made MILLIONS of these things in the '40s, and new-in-wrap surplus mags are still available. I have 5 mags of various capacities that I've modified, so that's my viewpoint on it.

[MadDogDan]

Since I really don't care about the collector value of a true TSMG mag and can't afford a FA Thompson to use them in, I modify the mags and not the mag catch. That way I can use both Thompson mags and the Semi Auto Ordnance mags, whichever I can get my hands on.

[MisterB]

Since I really don't care about the collector value of a true TSMG mag and can't afford a FA Thompson to use them in, I modify the mags and not the mag catch. That way I can use both Thompson mags and the Semi Auto Ordnance mags, whichever I can get my hands on.

That's a very good point

[dadwasajarhead]

You will find that you continue to have jamming problems, even after you elongate the mag catch hole, until you remove some metal from the front of the mag on the edge that is just below the magazine's lifter. The bullet needs to be completely free of any obstruction so that when the bolt comes into battery the cartridge is not tempted to flip up. It should be a direct, unobstructed shot for the cartridge to go into the chamber.

 

Take the floor plate off of the mag. Remove the spring and lifter. Take a Dremel with a cylindrical grinding stone (or a flat bastard file) and file on the front edge, between the side wings. You shouldn't have to remove any metal from the back edge, because if the bolt strikes the mag at that point the mechanism wouldn't go into battery at all.

 

Regards

[Syxtnyne]

I have a couple of modified mags that I would trade for USGI mags. I just got work on my tommy and had the USGI mag catch installed so now my mags are useless to me.

[Syxtnyne]

Here's the M1A1

[Merry Ploughboy]

You will find that you continue to have jamming problems, even after you elongate the mag catch hole, until you remove some metal from the front of the mag on the edge that is just below the magazine's lifter. The bullet needs to be completely free of any obstruction so that when the bolt comes into battery the cartridge is not tempted to flip up. It should be a direct, unobstructed shot for the cartridge to go into the chamber.

 

Take the floor plate off of the mag. Remove the spring and lifter. Take a Dremel with a cylindrical grinding stone (or a flat bastard file) and file on the front edge, between the side wings. You shouldn't have to remove any metal from the back edge, because if the bolt strikes the mag at that point the mechanism wouldn't go into battery at all.

 

Regards

 

Rather than take the magazine apart, what I have done when working on the lips and edge area is to push the follower down past the catch hole with a dowel, stick a 1/4" rod sideways into the mag through the catch hole to hold the follower down while the work on the lip area is performed and take out the dowel. After the grinding or bending is done, again use the dowel to push the follower enough to release the 1/4" rod, and then ease the follower back to the top. For metal removal, I generally use the hand held motorized grinder rather than a file of unknown parentage as I'm hoping to avoid carpal tunnel.

 

MHO, YMMV, etc.

[elkoholic]

I thought once the "modified" catch was in, it would then take ww2 and Kahr mags?

[MisterB]

I thought once the "modified" catch was in, it would then take ww2 and Kahr mags?

No, you can't have it both ways.