MrTuffPaws said:
I really don't think a glasser or magsafe is going to do much out of such a short barrel, but I may be wrong.
That would be true of many other cartridges, but .25 ACp was built around guns with 2" tubes. All .25 ammo is designed to be used in very short barrels.
As to the original question, .25 hand-down. Here's why:
1: power) While .22 LR is typically higher in ballistics tables, remember that even handgun velocities for .22 LR are generally obtained using 6" barrels. Most published data is in 20" rifle barrels. Out of a 2.5" pistol, the .22 LR will not develop the 140-170 ft/lbs. it is often rated at. Power of the two cartridges from identicle barrel lengths is virtually identicle.
2: bullet design) .25 is far superior in this department. It uses standard JHP or FMJ bullets, while .22 LR uses externally lubricated heeled bullets of lead or copper wash lead.
3: Case design) Rimmed cartridges do not have a good track record for reliable feeding in autoloaders. The .25 is a semi-rimmed case that was specifically designed for small automatics.
4: quality) Even premium .22 LR is not as well made as .25 ACP ammo. Bottom line is, centerfire is better. I simply expect duds when shooting a .22. For a defensive gun, it is worth the price.
I have a couple of mouse guns in each caliber, and the .25's have proven much more reliable.
All that said, Speer has a 35 gr. JHP Gold Dot loading that is fairly potent as .25's go. I have tested them in ballistic clay and they performed quite well, though .25 ACP seldom delivers more than 7 or 8" of penetration- regardless of bullet type.
You would be much better served by a .380 and the little Kel-tec is as small as and lighter than many .22's and .25's.