What Njanear said..I have a couple a BSA Prefix G-27, a BRU prefix G-26 and a BTN and BPL baby also, (G-26/27) all 2.5 Gen. You should have a serial # starts with "B" I bet, never seen a "C" and grooves were there by the "D"'s.
The Glock factory (+)2 was made for them, no checkering!
GLOCKS #1 FAN!!!
"IN GLOCK WE TRUST"