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

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You will need to have a .400" barrel blank cut to your needs, Colt pattern barrels are easy to make, cut the chamber end to fit the upper, and everthing forward of the barrel nut is optional.[/blue]
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No, it would require the opening of the bolt face slightly to accept the .423" diameter case. The extractor would need adjust also.[/blue]
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Any of the current mag Colt pattern blocks, or the Hy-Tech block, as you can feed 40/357-SIG from a std 9mm Uzi mag.... Barrel Exchange is already doing it for another Uzi caliber option since early 2003.[/blue]
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Refer to answer given for #3.  40 S&W is another option for me, as I have maybe 7500 free 40 brass given to me. [/blue]

thanks for the insight SBR

check  with  OLY arms, they  make  most  any upper  you  would  want, and  there  customer  svc  is  OUTSTANDING.

Well, it won't use Uzi mags though...as Oly has their own system for pistol cal. uppers.

The only person I know of that has done other pistol cal. in a Colt style pattern is Kurt.  He's made a 357 Sig upper in the Colt pattern.  He can rechamber a 9mm barrel and open up the 9mm bolt face.  He has a section under "Industry" (up above).  There might be a few other people that can do it, but I know he did for sure.

Most of the Q's have been answered by SBR....


(I know of one member who has a 357 Sig upper.  And I'm currently gathering parts for one myself.)

I am going to jump in here knowing next to nothing so excuse the very basic questions.

1. There are two patterns, Colt and Oly? Colt systems lock the bolt back and Olys don't?

2. Does one need a special upper receiver to run a pistol caliber or will a standard 5.56 flat top work?

3. After a bolt and a barrel the only other thing one needs is a mag block? to fit whatever magazine you are going to be using?

The idea of a .40 cal upper is very nice as I shoot an STI .40 for IPSC so not having to start up a 9mm press is WAY appealing.

IPSC_GUY sends

Yes, there are two major patterns.  There are one or two other types that have their own system, but are 9mm only.  Oly came out w/ their's then Colt did (from what I have read).  The Colt system only locks back IF you are using factory Colt magazines and an adapter block that will activate the factory 223 bolt hold open OR you replace the 223 bolt open w/ a 9mm one.  The diff. is a longer bolt open then w/ the 223



A standard 5.56 upper rec. will work.  The only difference is on the dedicated pistol is there is no forward assist and brass defelector cast into it.  The pistol cal ones have a plastic deflector that is held on by the ejection port cover.  And there is no gas tube hole.  But they are essensially the same (It'll work).




A stronger recoil spring maybe needed and/or a heavier buffer.

Oly makes a 40 Cal upper now.  But the mags have a tube welded on so that no addapter tube is needed and you use the standard 223 mag release.  I think Stens can be modified so that 40 will feed from them, so a SOCOM block can be used w/ unmodified Stens (but it uses a paddle release).  The block is held in by the 223 mag catch, so if you forget, you drop the mag AND the adapter.

A Colt pattern 40 will be a CUSTOM thing.  Custom 40 SW barrel and opening up of the 9mm bolt assembly.  So it will end up costing a bit(?) more.  There are a number of adapter blocks out there made to work w/ the Colt style.  RRA, ASA and a few more make blocks.  There is even one to use unmodified Uzi mags (it's been reviewed here, can't say I've read in to it).



Again, the cheapest and quickest is to get an OLy 40 upper.  But it has no hold open and you can risk dropping the block when using a SOCOM block.  Don't quote me on what mags they use at this time.  Hope this helps.

Edit- Kurt of Kurt's Kustom Firearms has made 40 and 357 Sig uppers in the Colt style.