Has anyone built an upper in 38 Super? I'm curious as I'm looking for my next project or should I just forget it  and go to 10MM.

I haven't built a .38 Super upper, but I think it is a great idea!  So would a 9x23mm!

What magazines are you considering for this project?

Just guessing, but it would probably take a heavier than standard buffer to accomodate the .38 Super, at least with the loads I would want to run through it.

My experience with 16" carbine barrels is that they give you the ballistics of a warmly loaded .38 Super out of a Gov't model pistol.  Or pretty close, anyway.  

The problem with those velocities is that very few bullets are constructed to perform well going that fast.

I just started thinking about this project. I don't know if I could use sten mags. Cartridge lenght will be an issue. Just gonna sit down one night and measure case lenght. Since I want to use an exisiting lower receiver that I have, grease gun mags are to wide. I am toying with this at this time. It's probably a lot easier making the gun in 357 sig.

Quoted: I just started thinking about this project. I don't know if I could use sten mags. Cartridge lenght will be an issue. Just gonna sit down one night and measure case lenght.

Max OAL for Super is 1.270"..... You might be able to pull it off with STEN mag, but it most likely would require the use of  "FP" bullets to keep the OAL down.   Here agian, not sure how the std Super case will stack, with the slight rim on the rear, though the rimless Super  or Super Comp be better idea.

I have loads of 38 Super and Super Comp brass, no FP bullets though,  I could try them in the Sten mag and se how they stack.

Best Easiestroute would be using CZ 24/26 mags for the 7.62x25 Tok, and then a lower that will take the wider mags, either the Cav Arms or the up and coming MGI Modular.

Other route is the Ppsh43 mag for the 7.62x25 Tok, but these require a custom made mag block ..