Is what the so called expert at the local gunshop told me. Something to do with extractor and head space? He said it is ok to switch 40 to 357 as case heads are identical and vis versa. Told him I know of many people that have conversion 9mm barrels in their 40's and have had no trouble. His reply "you are just asking for trouble by doing this". Then why in hell do they sell conversion barrels in the first place. Idiot! Just thought I would share my latest experience as I am getting closer to my new purchase. Either another service 40 or the sub 40. Also this same gunshop is charging more for the package with the SC, meaning the one that comes with holster and high cap mag. I thought this was free just as with the free rounds with the 45 GAP when you buy the XD 45GAP. Figured that I would just buy one and mail SA to get the extra's.