hello, you are correct. there are type 1, 2,3 etc barrels. it generally refers to things such as sights, markinge , etc. You may find on older frames ( non easy open ) that newer barrels will not work without some modification. Sometimes a matter of the locking bolts, but more often than not an interference between the opening lever/trigger guard and bottom of the barrel lug. Newer barrels have a bit more material under the hinge pin hole than the oldest barrels ( not talking about the "step lug" here, up front on the lug under hinge pin hole. If you get an easy open frame or a G2 you should have no problem. Unless it's a really good price I'd pass and get a easy open frame or G2.