Either way, I think it is a mistake for Glock to not build a single stack in any other caliber. If you notice, tho, Glock tries almost every new idea in the U.S. with a .45 variant. The 21 was the first model to have finger grooves, then the first to have rails. The 36 was the first single stack (and so far the only one, darn it). The 45GAP was Glock's first attempt at a proprietary caliber. Now the 21SF is the first model with a piccatinny rail and an ambidextrous safety. They seem so have the linear approach of limiting their new stuff to the .45 caliber. Oh well, back to the original thread.