Join Date: Jul 2012
Location: The 13th colony
I echo what GB said about shooting 40 in a 10mm. Yes, in some guns it may fire, but it may not be reliable and could possibly cause damage to the gun over time. Since both cartridges are designed to head space off the mouth, the 40 can't reach the stop in the barrel (not sure if there is a technical term for that point). Therefore, the 40 will have to be head spaced by the extractor which only supports the case on one narrow point on the rim of the case. If the extractor doesn't hold it well when being struck by the firing pin, it may push the case forward and you will have a failure to fire situation and it may push the cartridge further into the chamber where you will have to pick it out. Also, overtime, it could damage your extractor in which it may begin to fail to extract, which is another serious issue.
All that being said. If I was in a SHTF scenario and all I had to put in my 10mm was 40, I would use it. However, I wouldn't use it on a daily basis or even for practice to save $$. It should be a last ditch effort where you really have to use it.
If you really want to shoot 40 S&W in a Glock 10mm, you can guy a 40 barrel for that gun and safely shoot 40 out of it without any fear of function or damage.
Go Donald Go!!