Kel-Tec had one, called the P-40. They also had some conversion kits for the P-11, which basically called for using the existing P-11 Mags, and then putting a new slide and barrel on the existing frame. These didn't do so well, the magazines constantly jammed. The first pistol I mentioned, the P-40, was an updated design that actually used magazines that could handle the .40 S&W cartridge.
I owned one, it was given to me because the previous owner didn't really care for it that much. I maybe shot 200 rounds total through it before I sold it. Recoil was harsh, feeding from the mags was erratic (I don't "limpwrist"), and I had jams from every 4th round in the magazines. This was going to be my carry handgun, but it wasn't reliable enough for target practice, let alone carrying. The final straw was when my right hand was numb from firing 4 magazines through it and the webbing in my hand was bruised (how the hell does one do that?). I finally saw why it had been given to me.
I think Kel-Tec was onto something with the P-40, but had problems executing it (like they tend to have with some of their new guns). However, there are some rabid P-40 fans out there who swear that everything is operator error. I think it's just too powerful a cartridge in too light a handgun. If your buddy is looking to sell it, toss it up on the Kel-Tec Owners Group
www.ktog.org, these guys are the ones who know how to fix Kel-Tec issues and have a solid appreciation and rabid fascination with the Kel-Tec Product line. He should get a good price and he will know it will be going to a good home. Or, he can contact Kel-Tec and get a .357 Sig barrel for his P-40. It uses the same mags and slides I believe.
Good Luck.
