I know these are two different cartridge types but what is the difference between the two? Both cartridges look very similar to me.

The GAP was invented for glock pistols to have a slimmer grip for persons who have smaller hands. I believe the performance of the two rounds are identical. en.wikipedia.org/wiki/45_GAP

Or try this one. www.thegunzone.com/glock/45gap.html Between me the Donut Slayer you should have it down pat...

Darn Donut Slayer...Yer just a minute faster then me...

Thanks for the info fellas, very interesting how one large (albeit very good) gun conglomerate can a brand new round invented just like that. I've considered a small glock as a carry weapon so that is very helpful to know.

Building a better mouse trap is a hard thing to do when you take on something like the 45 ACP.
The basics of what Glock did was: they shortened the ACP case a little, ran the pressure up and changed the primer to a small pistol primer. The original idea was to only use 185gr. and 200gr. bullets.
On the surface it appears they reinvented the 45 ACP. Ballisticly they are about the same.What they did do was build a compact pistol that works.

Most die hard 45 fans I know do not like the GAP and think its gonna die off like the 10mm did. I belive it has it's good points but also think it will die off, just not as quick as some would like to see.