M3 mags mods for MAC 45

[ferndog1]

Someone posted a while back asking how to modify M3 grease gun mags for a MAC.
I knew I had this image, but just recently stumbled across it.

 

[Deerhurst]

Good info. The Lage dual latch is easier.

 

[Slowmo]

Thanks! I was looking for that a few weeks ago!

 

[woodenword]

Ok, so I’m new to the fat MAC. Mine came with a couple modified mags. I bought the dual mag catch. So now I’m confused why you would have needed to modify the side stops. The dual mag catch doesn’t sit the mag any lower in the mag well, the catch is just lower. With the dual mag catch, I haven’t done anything to surplus M3 mags and they work fine. What am I missing here?

 

[timkel]

When you use unmodified M3 mags, the mag does sit lower.

 

[Deerhurst]

When you use unmodified M3 mags, the mag does sit lower.

How so? The feed lips must be in the same location or it will not feed/will jam.

 

[woodenword]

How so? The feed lips must be in the same location or it will not feed/will jam.

Ok, looks like timkel is correct! Measuring it look like the unmodified M3 mag sits about 3/32” or .093 lower than the modified mag! So, the feed lips sitting a little lower isn’t a problem, cause it works!
Learning every day!

 

[Deerhurst]

0.093 is a LOT! I would expect issues unless the mag is already so high it has the radius of a 45ACP or more that it could move and still have the bolt strip a round from the mag.

I will have to check some mags. Did you measure the mag to make sure it's just not shorter to where the catch holds it?

Pretty sure the entire point of the dual catch is to allow the unmodified mag to sit at the same location as a modified mag.

 

[theduke]

I found some site the other day that clearly showed 1/32"

was the majic number to convert GG mags.

I wish I would have copy/pasted that info.

I'm on a mission now.

 

[woodenword]

0.093 is a LOT! I would expect issues unless the mag is already so high it has the radius of a 45ACP or more that it could move and still have the bolt strip a round from the mag.

I will have to check some mags. Did you measure the mag to make sure it's just not shorter to where the catch holds it?

Pretty sure the entire point of the dual catch is to allow the unmodified mag to sit at the same location as a modified mag.

I was measuring the top of the feed lips of mags I have ran multiple times. I’m very surprised!

 

[Slowmo]

How so? The feed lips must be in the same location or it will not feed/will jam.

As shown in the drawings, a SMALL amount of material is taken off the insertion stops on the sides, meaning the mags can insert further into the magwell, which means they can potentially ride higher. Whether they actually ride higher would be controlled by the magazine spine, mag catch, and magwell. Sam states that there are at least four different magazine wells for the M10, which is why mag catches may need filing.

 

[Gaujo]

I strongly suggest you do not do this to a good grease gun mag

 

[Jack007]

Over the last 40 years I have used many GG mags in my M10/45 guns without any mods to the stops. I quit grinding them down years ago.
That said, my original PS/Marietta MAC stamped mags all have the stops milled.

 

[timkel]

I'll stick to the original Ingram design. So I modify all M3 mags to fit.

 

[Deerhurst]

I run completely unmodified GG mags though I do have some modified mags as well.

 

[woodenword]

I run completely unmodified GG mags though I do have some modified mags as well.

The unmodified GG mags I have, would not lock in till I installed the dual mag catch.

 

[Gaujo]

I'll stick to the original Ingram design. So I modify all M3 mags to fit.

You know I want to say I read/heard that Ingram's original design used standard grease gun magazines and it was actually a MAC decision to mill the ledge off. Anybody else got thoughts? Not sure.

 

[Deerhurst]

The unmodified GG mags I have, would not lock in till I installed the dual mag catch.

Weird. What year/stamp M10?

Mine is a 1973 Powder Springs.

 

[Deerhurst]

The unmodified GG mags I have, would not lock in till I installed the dual mag catch.

Same. The mags themselves are completely unmodified.

Gun has a dual catch.

 

[timkel]

You know I want to say I read/heard that Ingram's original design used standard grease gun magazines and it was actually a MAC decision to mill the ledge off. Anybody else got thoughts? Not sure.

Yes, that is true.
This Modified M3 mag came with a NIB pre-auction Powder Springs Ingram M10.