One of the most successful handgun designs ever, there are so many Glock
models that it's hard to keep them straight. In this country, the two most popular calibers are 9mm and .40 S&W. You'll most often see them in full size guns (Glock 17 and 22 respectively) or compact models (19 and 23). Glocks have seen widespread use with our military with various units, regular and elite, even though they haven't been officially adopted. The Ã¼ber-elite Delta Force operators reportedly carry Glock 22s in .40 S&W.
First, the caliber question--while I have no doubt the .40 S&W will perform better against enemy combatants than the 9mm, especially in FMJ form, until that caliber is adopted by other NATO countries you will not see it as the caliber of our official military pistol.
If I was writing this a few years ago I would have no qualms recommending the Glock 19 as the replacement for the M9. It's markedly smaller than the Beretta while having the same capacity, has a shorter trigger reach, and is disgustingly reliable. Again, the trigger is a little heavy and mushy, and metal night sights would be a necessary upgrade, but overall it would be a great idea€¦.if it wasn't for the Gen4 Glocks.
Everything that was wrong with the Gen3 Glocks (trigger pull, plastic sights) went unchanged in the Gen4s, and they 'fixed' a number of things that were working just fine (recoil system, magazine release). The recoil spring of a Gen3 G17 is 17 pounds, which is almost too heavy to begin with. The Gen4s put the double recoil spring system of the .40 S&W system in all their 9mms€¦and now is selling retrofit kits so that the guns will run. The adjustable backstraps on the Gen4s make so little difference (4mms in length between the smallest and largest) it makes you wonder why they did it€¦.actually, the reason they did it, was the last pistol I'm going to take into consideration€¦