I posted this on in the pistol caliber forum ,but it may fit here. To clarify I want a sbr in 9mm smg specs in 40 caliber-

I would like to have a colt style sbr in 40 cal. I want to use my preban registered lower, and use either colt or uzi mags with the feed lips slightly modified for the larger case.
1. Were would I obtain the upper?
2. would the colt bolt assembly function without modifications ?
3. what would be the best mag block for this conversion ? (this would be a permanet modificationI would not switch back to 223.
thanks for the ideas and feed back in advance

Ok what are my options and what are the draw backs?

4.one more question instead of 40 caliber what if i wanted it in 357 sig

Kurt's Kustom Firearms...  I've seen his builds on his website of (if I remember correctly) both .40 S&W and .357Sig.  I've not dealt with him (Kurt) but the only remarks I've heard about him are very good.  He's in the Industry section, and website is below.

http://www.kurtskustomfirearms.citymax.com/page/page/8932.htm

Brian

Check the Olympic Arms web page. They sell one in .40. I have been shooting one of their PCR .45's for a while. Mine is post ban. Works very well. Oly Arms would be much cheaper/faster than kkf.