Yes! This is what I was referring to originally. There will be some space between the sides of the mag and the magwell since the UMP mag is thicker but yes, single stack USC mags work in a UMP conversion. Your UMP is or should be already 922 compliant when you convert it. I think SG is talking about placing an over 10 round mag is a stock USC.Will USC mags fit in a UMP conversion or not?.
You can modify a .40 S&W UMP mag for .45ACP but it is a slow painful process and you need the .45ACP follower for everything to work out. Ribs inside mag need milled to fit .45 follower, feed lips slight adjustment and opening. Otherwise it is a piece of cake (sarcasm). and .40 mags seem to be a little more plentiful. I am working on a mod now as I have a bunch of .40s I picked up from a local dealer cheap (from the full-auto range guns rotation). Has anyone else tried a skilled hand at this?Thanks to all for the clarification. Good to know that only for loss of 5 rounds I have a fallback until the HK mags come available again. The loss of 5 rounds s offset by no needing to but US floor plate and follower for compliance. Believe a few are trying to make a US UMP 45 mag but nothing has hit market yet.
I had the same issue on a Promag SL8 mag, try sanding the feed lip just a bit to remove some material.I picked up a 10 round pro-mag for my ump conversion to see how it will work since HK ump mags are not yet available. The only issue I've encountered is that this mag will not lock into place unless bolt is pulled back. Otherwise, it feeds & chambers OK.
Man, that blows. The HK USC mags will work and lock in on the conversion and that was what I was responding to. These are pro-mag mags and we all know what kind of rep they have for reliability. Can you return it and try to get your $$ back?Just received the Promag 20 rd USC mag that I bought under belief it would work in a USC/UMP conversion. They do not work in the USC/UMP conversion. They won't lock in and have a 1/4" on both sides of magwell. Oh well lesson learned and $40 down the drain unless i can resale to somebody with a USC and the appropriate number of US ma parts in FCG. Guess will just have to wait for UMP mags to come available hopefully at reasonable price. Will try to post pictures once I get to my laptop versus iPad.
As the clean version goes: "Fecal Matter Happens". Not going to sweat it and it definately isn't the most expensive mistake I made (that one is probably believing the car salesman who told me sure Nissan makes an adapter to put a baby seat in the back of the 300ZX, you don't need the backseat version, a new LT should have the two seater. My wife still doesn't let me forget that one). Anyway will try to see if anybody else can use it and see what I can get out of it.Man, that blows. The HK USC mags will work and lock in on the conversion and that was what I was responding to. These are pro-mag mags and we all know what kind of rep they have for reliability. Can you return it and try to get your $$ back?