My favorite set of videos showing the barrel length when a .22 WMR wakes up a bit compared to .22 LR.
3" barrels with separate chambers. A 4.3" barreled pistol with integral chamber ought to be similar.
The 22 Mag cartridge shoots at the same pressure as a 22LR. That's why it can be chambered in similar rifles. It gains its velocity advantage by maintaining that pressure longer. In order to maintain the pressure, it requires a longer barrel. Fired from a 2" snubnose, you'll see no velocity advantage over 22LR.
Check out the 40 grain bullet ballistics with a 2" barrel:
BBTI - Ballistics by the Inch :: .22 Results
BBTI - Ballistics by the Inch :: Results
Both produce velocities in the mid 800fps range from a 2" barrel.
Most 22 Mag ammo is loaded to make maximum velocities in rifle length barrels. This produces an amazing amount of blast and flash when fired from pistols. There are 22 Mag pistol loads and if you must use 22 Mag for defense they would be a good idea.