Glock Vs Glock

Again in GURPS terms...

The Glock 19 is 0.1 lb. lighter (2 vs 1.9) and each magazine is 0.1 lb. lighter (0.6 v 0.5) than a Glock 17.

You lose a point of damage (2d+2 pi vs 2d+1 pi) and two shots per magazine (17 vs 15).

Average hit is 9 vs 8.  Each magazine will do 153 for the 17 and 120 for the 19.

The 17 and two magazines is 18 turns of firing and six turns of reloading.  Starting with one in the chamber it's 3-3-3-3-3-3-reload (3)-3-3-3-3-3-2-reload (3)-3-3-3-3-3-2.

The 19 and two magazines is 16 turns of firing and six turns of reloading.  Starting with one in the chamber it's 3-3-3-3-3-1-reload (3)-3-3-3-3-3-reload (3)-3-3-3-3-3.

For GURPS there's not much reason past saving 0.3 lb. and hoping being short 6 rounds and a point of damage per shot doesn't affect the outcome.  In real life it's just enough smaller to be easier to conceal.

Is 2d+1 pi enough?

Ball does 3-13 (average 8) on an unarmored, clothed person.
Hollow points up things to 2d+1(0.5) pi+ giving 4-19 (average 10).

An average of 10 with hollow points is certainly enough to get a consciousness roll!  Landing three in the torso is getting two death rolls too, and they're all major wounds.

That'll do for most gaming gunfights where a pistol will do.