i have a USP 45, was considering buying an aftermarket barrel, which is a better caliber, accuracy, ballistics and cost, 400 corbon or 45 super?

45 Super same chamber as 45 ACP.I believe the full size USP is rated for the super.

From what I've heard, the .45 Super requires some frame mods to beef it up. The .400 Corbon is a straight drop-in, in most cases. To be safe, I had my Springfield fitted by SSK. A heavier recoil spring is required (22lb.) to protect the frame from being battered. I've been shooting 135gr. bullets and it is awesome, 1400fps from a 1911-style gun! Brass is available at Dillon, as well as the dies and 135gr.HP Rainier bullets. You can get more information at: [url]www.corbon.com[/url]

Here is the link to the 45 Super stuff:
[url]http://www.acecustom45.com/[/url]
The conversion kits are only listed for 1911 Style Pistols, S&W Pistols and Glock Model 21s.
There is nothing listed about having to "beef up" the frames, but it does mention some machining is required to fit the kits.
From what I can tell, there are two types of .45 Super ammo being loaded up too, the .45 Super and the .45 Super Tactical.
Check out the FAQ for info about HK conversions.

I've been thinking of having my S&W 4506 converted over and the whole concept seems pretty sound to me. Being able to switch back and forth between regular .45 ACP and .45 Super sounds like a good deal.