GP100 is the series model.
KGP (K is for STAINLESS)
KGPF (F is for FIXED sights)
GP (Not preceeded by K means it's BLUED)
1 = 100 Series
3,4, or 6 is barrel length in inches
0 = HALF SHROUD; 1 = FULL SHROUD
161 = 100 series, 6" barrel, FULL SHROUD
I have a KGP-160, Which is a Stainless, 100 Series, 6" barrel, HALF SHROUD. They stopped making the Half Shroud model in 2003. The 1/2 Shroud model is 3 ounces lighter. 43 ounces as opposed to 46 ounces.