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Discussion Starter · #1 · (Edited)
I'd like to hear from everyone that's done the complete conversion themselves.
1) Do the UMP lower front locating hooks need to be fitted or opened up to mate correctly to the USC upper?
And if so, is it easy to do CLEANLY at home?
2) Can the magazine port opening in the USC upper be opened CLEANLY and neatly without buggering the bottom rails at home?
3) Is it easy to open the hinge pin hole evenly in the HK butt stock with a round file to fit the B block ?
I'm trying to do as much as I can to cut the conversion price down, $pending more on conver$ion part$ than a new USC without any mag.s is a little deterring. It's amazing a real NIB UMP costs $1140. for L.E. Thanks
 

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1) Do the UMP lower front locating hooks need to be fitted or opened up to mate correctly to the USC upper?
And if so, is it easy to do CLEANLY at home?
Yes and yes.
2) Can the magazine port opening in the USC upper be opened CLEANLY and neatly without buggering the bottom rails at home?
Yes, trace around the OD of a UMP mag when placed in the upper receiver magazine opening, only the feed lips will fit in the opening. This will be your template to make your cut.
3) Is it easy to open the hinge pin hole evenly in the HK butt stock with a round file to fit the B block ?
Yes, but a drill bit works better
....
 

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Discussion Starter · #3 · (Edited)
OK so what is used at home to open the mag port opening in the upper and how do you keep the depth shallow so as not to hit or bugger the rails? Also what's best to use on the hooks to start with and then sand finish to fit? I saw a post somewhere last night and just found it on ARF, but a mill was used --> USC to UMP Conversion Tutorial - AR15.COM
 

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After tracing, use an Ex-acto knife (big thick blade) and repeatedly cut a trough around the inside of the tracing with a straight edge. This will make it smaller, which is what you want. After you have scored a trough use a dremel or wire saw and slowly remove the excess. You will be far away from the rails. When done use a flat file to remove additional material until the mag fits like a glove and check for function. Use steel wool to de-burr. Remember always stay on the small side and check frequently as to not over sizing the opening. There is a tutorial on barf-com that is real good if you have access to milling equipment. On the hooks, cylindrical chain saw file and as before check frequently, steel wool etc., etc.
 

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Discussion Starter · #6 ·
How bad is the quality of the M3 conversion lower? I've seen some post stating quite a bit of adjusting and modifications need to be done to get a good fit and function. Seems this route is much cheaper and easier than spending what two real UMPs cost for one USC conversion?
 

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Discussion Starter · #8 ·
More than a few hundred dollars, from my figures ?
FBI lower 399.95
Stock Block B 194.95
HK Butt Stock194.95
Butt Stock Pin 25.95
US Trigger 134.95
US Sear 46.95
Total 997.70
Plus machining machining vent slots and purchasing rails and unavailable mags?

Verses $240. shipped for M3 kit and $30 each for new 30rd US mags?
Plus purchasing rails and having slots milled.
 
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