My $ .04
You will get a huge speed boost from a rifle barrel. I experimented a while back with some .357 110, 125, 140 and 158 gr HP bullets loaded at the top end of performance for a 4 inch .357. On paper, all bullets suffered a "total failure" when shot from a 20 inch carbine. What that means is that each one "splintered" and separated from it's jacket.
In less technical terms, the bullets fragmented after about 1 inch of penetration. The jackets peeled off about an inch later and were torn apart. The cone of destruction was 30 - 35 degrees off center line. Penetration was 6 - 8 inches. There was, in most cases, no significant central mass to measure retained weight. The test media was dripping wet news print loosely packed.
In short, after about 1 inch of penetration the bullets exploded and the fragments traveled about 6 more inches as much as 30 degrees off the original path, and the mess created was spectacular.
Solid bullets traveled 3 times as far in the test media, but started to tumble an divert from their original path after 4 - 5 inches.
I wouldn't want to get shot with any of them. I believe that a solid torso hit with any of them would be fatal even if it happened on the steps of an ER because the damage to any organ in the vicinity of the point of entry would likely be un-repairable. That does not mean to imply that such a would would be instantly incapacitating. Certainly these loads should not be used against thick haired or very large game animals.
I keep a 20 inch Rossi 92 in my home with an attached surefire and loaded with the 110 gr ammo. Several months ago I flattened a wild dog with it late at night. Very impressive. The dog was a German Shepard mix. 1 bullet through the chest cavity left an exit would 2 inches in diameter. A second bullet through the guts did not exit, but did pretty well destroy everything in it's path.
FWIW.