I am new to the forum and you have probably had this question before, but here goes. I need to know what the differences are in the Gen numbered Glocks as I plan on buying a used model 22 and installing a .357 sig barrel in it. The barrels I have found say Gen 4 barrels. The pistol I have waiting on me at the local dealer is older than that. I was wondering if that barrel will work in an older model Glock. Thanks.