i have a older sig p226 in 9mm (made in west germany)can i just buy a .40 s&w barrel and drop it in or do i need a complete slide . i know i need to get a different mag, any help would be appreciated.
Do not try to shoot .40 in your older P226 9mm (2 piece slide). I am not aware of any conversions that will work with that gun. Sig redesigned the slides and eliminated the pinned breach block in order to handle the bigger caliber
You would need a whole complete slide and mag to make it work.