We all call these a Model 1910 these days, but Mauser simply referred to it as the 6.35mm. Yes, it's a .25 ACP. It is by no means a large gun, but it's not as tiny as most .25s, I can actually get a good two-fingered grip on it. This one is in very good condition, with small signs of age, but not much of use. It has a 9-round magazine, and like it's .32 cousin it locks open on an empty magazine, and the slide won't drop until you insert another (it doesn't have to be loaded.) The safety, located behind the trigger, is activated by pushing the lever down and released by pressing the button below the lever. It's a handly little gun, with an excellent trigger. The sights are very good for a pocket-pistol of this era. Hell, they're better than a lot of service guns from the period. Recoil, as you'd expect, is negligible. Here's a pic of it with a more typically-sized .25, Linda's Colt Junior. The second picture is with it's 'big brother,' the 7.65 model of 1914 The Mauser has a 3" barrel, and picks up some velocity and energy over 2" .25s. My standard reload for .25 ACP is not at all a 'hot' load, and consists of a hard-cast 58gr. LFP over 1.1gr of Red Dot with a CCI 500 small pistol primer. This load makes 646 fps. and 54 ft./lbs. out of the Colt Jr., and makes 729 fps. and 68 ft./lbs. from the Mauser. This relatively small increase in velocity has a disproportionately large effect on penetration. Using this load the Colt penetrates 12.5" of Clear Ballistics 10% ordinance gel. From the Mauser out of eight shots one stopped at 15", the other seven passed entirely through the 16" block. I've got cases and bullets inbound, so I'll do some more testing and a full range-report after those arrive. I really like this little gun, and plan on shooting it quite a bit. I expect it will be pretty accurate in rapid-fire.