I just bought a Model 1 shorty upper for an AR/M16.  I bought a bunch of the DPMS/Gtech Frankenmags from various folks on the EE here.

Took it out to the MG shoot this weekend, and not a single mag would work.   I tired playing with the feed lip on one mag, it would only occasionally work, singles always than a jam.  A few times I would get two rounds before a jam.    GRRRRRR

I still have some of the all black no-name mags that I didn't bring, so I guess there might be hope that they will work, but is anyone else having feeding problems with the GTech/DPMS mags?    How di you fix it?

This thing looks like it should be fun, if..............if I can make it work.

Thanks

Well, it may be the mags, and it may be the upper itself.  Try this.

Take a standard 20 round GI 5.56 mag and load 5 of the the 7.62 rounds into it.  That will duplicate the standard mag that Colt supplied w/their 7.62x39 pieces.  If the rounds all feed w/o problems, then it would seem that you do have mag problems.  But if you get the same malfunctions w/the piece, you need to talk to Model 1 about what they sold you.