like what PF said,...GP100 is the general model number. specific model numbers would be like,... KGP-141, GP-160, KGP-161. what it designates is,.. "K" will mean stainless model, NO "K" will be a blued model. "GP"- is always there. first numeric is also always there. second numeric ex. 4, 6... designates the barrel length, and the last numeric is either "0" or "1",... "0" will designate a half-under lug, and "1" will designate a full under lug (under lug the full length of barrel). FYI,...this is just my own observation of how they use their model number, TIFWIW.