I don't consider the .45 GAP a failure. As a matter of fact, it's much more successful than the .357 SIG. The purpose was not just to get the Glock name on a new cartridge, it addresses a problem of grip frame size that couldn't be solved with the .45 ACP.
4 state police agencies have adopted the 45 gap; New York, Pennsylvania, Georgia, and South Carolina, and more are considering it. Why?
1. It fits in a smaller grip frame than the .45 ACP, which fit the majority of officer's hands better.
2. The stopping power of the .45 ballistics (.45 colt/.45 ACP/.45 GAP) are proven.
3. It does not have over-penetration issues like the .40 S&W.
4. In extensive testing, which came down to the .40 S&W vs. the .45 GAP, more officers preferred the recoil pattern of the .45 GAP to the .40 S&W, saying it was more of a "push" than a "snap" like the .40 S&W.
The .45 GAP is basically a .45 ACP shortened to the length of a 9mm. It makes sense. You've got .45 ACP ballistics in a smaller and lighter package. It seems perfect for a R45. If you were starting from scratch, and had to pick from 2 catridges that were brand new and had equal power/ballistics, wouldn't it make sense to pick the smaller/lighter one, especially if you were designing a ground-breaking small pocket pistol?