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Interesting... Might pick one up until the hk ones get back in stock.
Has anyone tried them?
 

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Discussion Starter #4
Yeah, they are just extended USC mags....Would be perfect for those individuals not wanting to take on the conversion or waste money on the grease gun option as I think th USC in stock form looks better anyway.

I think I bought the last of the UMP .45 mags west of the Mississippi. I found them local a week ago, just in time for my HDPS conversion... I bought every thing the guy had..... 6 mags for $350 :)
 

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They do work. But I will issue the standard caveat: inserting them into the mag well of a USC is considered the act of making/assembling a semi-automatic weapon that would be in violation of 922(r). And while 922(r) has never really been the *lead* charge, it certainly has been part of a laundry list of charges brought against really bad folks and there have been convictions.
 

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So then these would be a alternative for those that have a UMP conversion? I am operating under belief that they are US made so no 922R issues for those that have done the UMP conversion woth the required number of US parts. Want to make sure before I drop $ ordering some. Only 5 less rounds than the UMP 45 mag and they appear to be available but don't want to waste the money especially if they won't work or other issues I haven't thought of. This would carry me over until the HK mags hopefully become available again.
 

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Merchant of Death (Admin)
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As long as the base weapon doesn't have a parts count issue, you are good to go. And remember, 922(r) is not a possession offense, it's a making/assembly offense.
 

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Will USC mags fit in a UMP conversion or not? Have two different views above and just wonder whether they will fit and function even if a little loose in the magwell? I would have checked but I no longer have my original USC magazine. Just trying to see whether it is an option with the Promag USC 20 rounder since UMP .45 mags have dried up and unknown positively if they will reappear. Appreciate if anybody knows for sure.
 

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Will USC mags fit in a UMP conversion or not?.
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.
 

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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.
 

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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.
 

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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.
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?
 

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I am going to get 1 to try out. With the entire magazine being us made, the body, follower and base would all count as compliance parts. It should not matter how many compliance parts are in your gun... Right?
 

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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.
I had the same issue on a Promag SL8 mag, try sanding the feed lip just a bit to remove some material.
 

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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.
 

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I have one on its way to me, I am hoping now that since I did not modify my upper for the ump mags that it will fit. I figured it would br a little loose in the magwell, but as long as it locks in place it should be good for shooting paper. If it works, i'll buy yours.
 

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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.
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?
 

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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?
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.
 
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