I talked to the local machinist and he said it would take a few passes on each mag to make the proper cut. I think he's thinking of a 5/16" end mill, which is a little bigger than whats needed.  He's going to charge me $7 a mag. I measured the cut on a standard AR mag and on an Oly conversion sten. The cut is 7mm.  I figure if the machinist uses a 7mm end mill he could make the exact cut, and maybe bring cost down per mag, but I'm more concerned with having the right sized mag catch slot.

What size end mill was your uzi/sten mag cut with?  Is it an exact fit to the mag catch?  

The slot on my Oly Sten mag is 6.85 mm wide. In inches, that comes out to .269. I guess your machinist could use a 5/16 endmill (.3125), but I think that may be a little wide. The mag catch slot in a 30 rd. 5.56mm is around .263 wide. You could have him do a single pass with a 1/4"(.250) mill, and test the fit in your weapon. If the mag catch doesn't secure the mag completely, take a couple swipes in the slot with a file to widen it a little.

Actually yeah, the slot on my Oly mag is just a tad under 7mm too. The 5/16" is a little to wide and the 1/4" is going to be to tight.  Thats why I'm going to ask if he has the 7mm. The mag catch itself is 6.32mm, or 1/4" exactly.


A machinist has GOT to have end mills in the metric size...right?

For "real" UZI mags he better have Carbide.  Don't let him make the slot to sloppy.  All the slop (Mag, mag well adapter) adds up and causes problems. Makr the slot in the correct location and .010 larger than the mag catch.