How to tell if a barrel is 10ga or 12ga
 

I have a parker I am looking at, that has 2 barrels on it. 1 I know is a 12ga and 1 is a 10ga. There are no gauge stamps on the barrel lug as the barrels predate that stamp, I was assuming an RST 2.5 12 would drop further into the 10 than the 12, but I am not seeing that to be the case so far....

This is my first experience with a 10 so any help will be appreciated.

measure the chambers with a caliper

http://s73.photobucket.com/user/Gran...bfe6e.jpg.html

Thanks Rick, I figured it out though. It comes down to me being an idiot. The 10ga barrels are also 2 inches longer than the 12s.

Knowing that it became quite obvious that the 10 had a wider rim in the breech and the brass of the 12 shell doesn't completely cover it like it does in the 12s.

How about carrying a ten gauge shell with you when you look at guns? It will fit in a ten gauge gun but won't fit in a twelve.

This is the 1st 10 I have ever looked at, so I need to get some 10s.