There's more to the difference between 45 ACP, and 45 GAP than just length. The GAP's case is shorter than the ACP's case by .138" which makes it, roughly, the same size as a 9mm cartridge case. The 45 GAP round is, therefore, well suited to use in a thinner and more compact size pistol than the much longer 45 ACP ever could be. Frame width, however, remains the same. The bullet sizes are, also, different. The 45 GAP uses 185 and 200 grain bullets. The 45 ACP, typically, uses 185 and 230 grain bullets. At the present time it is not possible to use 230 grain 45 caliber bullets in a 45 GAP pistol - The chamber pressure would be just too high. Typical operating pressure for the 45 ACP is 19 - 21,000 psi. +P rounds can go up to 23,000 psi which, also, happens to be the almost the same operating pressure for 45 GAP which produces between 21 - 23,000 psi. (In other words, even with the use of a lower flash small pistol primer, the 45 GAP is already, 'maxed out' and has no room left to grow.) Interestingly, while these two cartridges have identical external case wall dimensions, the 45 GAP is NOT a, 'short' version of the 45 ACP, and shouldn't be used as such. It is NOT safe to fire GAP cartridges in an ACP chamber. Yes, it can be done, but not without significant personal risk. While the external case wall tapers are the same, the internal case walls are much different. If you cutback an ACP case to match the GAP's length, the GAP's internal taper is lost and 45 caliber bullets will bulge the case mouths when they are inserted. The case rims are, also, different. The GAP's rim is slightly rebated, and the extraction cannelure has a sharper angle to it. An ACP pistol's extractor might have a hard time consistently catching onto and digging into GAP rims. When it comes to recoil (and ease of recoil management) there's a significant difference to be considered: On the high end, the 45 GAP uses a 200 grain bullet launched at 21 - 23,000 psi and about 1,100 fps. The 45 ACP uses a 230 grain bullet launched at 19 - 21,000 psi @ and about 850 fps. That's a big difference! I have never shot the 45 GAP; but, I've been told that the recoil is very similar to a 40 S&W; and that statement seems reasonable to me. It, also, indicates that I'm not going to be running out anytime soon to pickup a GAP pistol. I'm very comfortable, very fast, and very accurate with the 45 ACP. Personally, I attribute a lot of this to the ACP's outstanding recoil characteristics. (And, to be perfectly honest, I have to suppose the 1,000 to 1,500 45 ACP rounds I fire every month, also, have something to do with my preference for and skill with this particular cartridge. Do I think the 45 GAP has much of a future in front of it? Well, people are people; and it wasn't too difficult for the, 'professional pistol users' among us to first gravitate to the new 10mm, 'wonder round' and, thereafter, to the new 40 S&W, 'improvement'. Yeah, I think it'll slowly catch on; but, at the same time, I don't see myself going along with the crowd. I've got my favorite CQB pistol cartridge; and, unless they come out with a new, 'photon laser', or some such, I really don't need the next new, 'wonder cartridge'. I'm fine with, and have a lot of confidence in, what I've already got.