You can swap 40/357sig barrels. I am in the process of buying a 357 sig barrel for my M40. I am not large man, so I like the compact sized pistols. If you can shoot the USPc you will not have any problems with the Steyr pistols. I have an HK USP45c and the Steyr is smaller. You will like the recoil on the Steyr pistols...compared to other pistols that I own in the same caliber...there is a significant difference in felt recoil. If you buy the older S/M series...you should almost be able to get 2 Steyrs for your HK. I just had my M40 hard chromed and the finish looks just as good or better than my SS USP. If Steyr ever comes out with a 45, I will probably sell my HK for a Steyr 45.