I have a Jetfire 950 in 25 acp w/ 4" bbl installed, and a Model 21 in 22 lr w/ 4" bbl installed. Both were bought and had the 4 inch outside threaded barrels installed prior to the 94 ban.
The idea behind the 4" bbl 25 was to increase the velocity of the ammo (1) - PPS MSC copper cookie cutter 29 grain hp's; (2) Glaser blues; or (3) CCI 35 grain gdhp's for straight penetration of the skull at angles compared to numerous citations of ball ammo following the outside curvature of the skull.
A similar effect with truncated cone 22 slugs was hoped for.
These are tertiary or quadruciary level back ups. They fit into a manicure set in the bottom of a shaving kit with 3 or 4 spare mags and a 4" liner lock knife and 2 50 round boxes of spare ammo just because it fits. Or in a paperback size testament cover in the suitcase. Or a diabetic glucose testing machine case.
Like the man said, they're nice to have around when you don't have a gun.
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"They asked would I fight for my country; I answered the FBI, yea!
"I will point a gun for my country but, I won't guarantee you which way."
Woody Guthrie