The new Model 31 looks just like the older Model 22 except for two external differences. It says "31" between Glock and Austria and it says .357 SIG instead of .40 S&W. There are some internal differences, too. The slide rails are larger, and the magazine case and follower are both stamped ".357." Otherwise in terms of weight and feel, you'd think you were holding either a Model 17 or Model 22. So, if these things are so similar, why would anyone want a new Model 31 instead of the proven 9 mm and .40 S&W models? The answer is simple: a lot of people in law enforcement, and a lot of honest citizens who carry firearms for personal protection, prefer the ballistics of the .357 Magnum. The Glock 31 and the .357 SIG caliber deliver those ballistics.
Since the Model 31 is pretty much the same gun as the Model 17 and Model 22, there's not a lot that needs to be said about it. The trigger pull is around 5 pounds. The sights are still plastic and still fragile. I picked the Model 31 rather than the smaller 32 or sub-compact 33 because the grip is larger. One of the advantages of all Glocks is their lightweight construction compared to steel framed pistols. So there's nothing special about the Model 31 except for the caliber. The new caliber and its apparent effectiveness is the story of the Model 31.
There have been lots of gun magazine articles about the .357 SIG. All mention that this caliber isn't a real ".357," but a 9 mm (.355") in front of a necked down .40 case. The use of the term ".357" is what computer people call a "marketing hack," a way of drawing attention to a new product. With the amount of powder that can be put in a necked down .40 case, and a 125 grain bullet, the resulting numbers are very close to the numbers posted by the older 125 grain .357 Magnum ammunition. The one thing you can't get from reading about the .357 SIG is the experience of shooting it in a Glock 31. So far I've fired just one .357 SIG load, the Federal Premium 125 grain jacketed hollow point. This ammunition retails for around $33 a box. I have two other loads to try out. The first is the Speer Lawman 125 grain TMJ (total metal jacket). That's a little less expensive. I also have a small amount of Triton "Hi-Vel" ammunition. The Triton box says, "115 Gr. BHP, 1425 fps/ 518 ft/lbs (4" bbl)."
The heavy bullet crowd might not like the 115 grain bullet at a high velocity (the Triton bullet appears to be the same one used in the Cor Bon 9 mm +P+ load), but I like the muzzle energy figure. Although the muzzle energy isn't as high as that produced by the Winchester 10 mm Silvertip, anything over 500 foot pounds is respectable.
So how does it shoot? When firing the Model 31, it is very obvious this is not a 9 mm or a .40 S&W. It is obvious this is the equivalent of a .357 Magnum. With the Glock frame, the recoil feels a little different from that of a Smith and Wesson Model 60 revolver, or the Model 13 or 19 or Ruger GP-100. The experience is a little different. The Glock's plastic frame does flex a little, and your hand is much higher up on the grip than with a revolver. With practice, you can get off two fast shots with the Model 31.
Where then does the Model 31 fit in the roster of Beretta, SIG Sauer, Smith & Wesson, Ruger, and another Glock that are cluttering up the safe? The Glock 20 (10 mm) with ghost ring sights is for IPSC shooting. The Beretta 92 FS is for bowling pins and plate matches where speed and high capacity pay off. The SIG 226 is for IDPA matches, the Ruger P-95 and P-90 are for teaching, and the Smith & Wesson 909 is for concealed carry. The Glock Model 31, at this point anyway, is in competition with the S&W 909 for the concealed carry application. The Model 31 is small and lightweight. So is the 909. The Glock is simple (pull the trigger), but the 909 works the same way. The 909 can, but not on a regular basis, fire the Cor Bon 9 mm +P ammunition, a very effective 9 mm load; maybe the most effective; maybe the only effective 9 mm load. The Glock 31 fires the .357 SIG and that is its advantage over the 909.
June 10 Update. Since writing these first words, I've fired several hundred rounds through the Glock 31. Only one round had a problem, and that was a MagSafe .357 SIG cartridge that left part of the case in the chamber after firing. I've also fired the Glock 31 with a .40 S&W barrel and had no problems in that caliber either. Some changes have been made to the gun: adding a Hi-Viz front sight, painting the rear sight flat black, adding a 3.5 pound disconnector to reduce the trigger pull weight, and adding an extended slide stop release. I also added a Safariland paddle holster to the setup. This is going to be my IPSC gun for the 1998 shooting season.
October 10 Update. One of my friends handloaded a lot of rounds for the Glock 31 in .357 SIG and we had some misfires. It turned out that the primer seating is critical, as is the bullet seating depth, head spacing, etc. The Glock 31 is out on New Mexico now, being used for ammunition testing. I wound up using the SIG 226 in several pistol matches while the Glock was away. When the Model 31 gets back, I'm going to replace the fixed rear sight with a Glock adjustable sight.