Yes. The 48 with it's half inch longer barrel has hundreds more FPS in velocity. Gives new meaning to the term hand cannon.

 

You can only ASSUME that a G48 will have a velocity advantage but you can't count on it.

I have chronographed different guns with the same barrel length and velocities can differ as much or more than 50 fps per inch from the same length barrel from an identical brand gun. And from different brands the difference can be even greater, but more depends on the individual gun. I once chronographed a 6 inch 357 magnum S&W model 66 and a 2 3/4 inch 357 magnum Ruger Security Six with the same ammo and the Ruger produced a slightly higher velocity from a barrel that was 3 1/4 inches shorter.

The general rule of thumb is that you gain or lose 50 fps per INCH of barrel and the difference in barrel length between a 43X and a 48 is .69 hundredths of an inch which is more than a half an inch but less than three quarters of an inch. the net gain would be about 30 feet per second best case scenario or you might not gain any velocity at all.

I'm wondering if it's possible to put a longer G48 barrel in the shorter G43 slde but it probably wouldn't be worth the effort or the expense for a a gain in velocity that might not even be there.

G43x barrel length: 3.41 inch G 48 barrel length: 4.17 inch

 

I'm wondering if it's possible to put a longer G48 barrel in the shorter G43 slde but it probably wouldn't be worth the effort or the expense for a a gain in velocity that might not even be there.

You can, but it's a worthless gain as far as velocity goes. Even if it increases velocity by +100, which it won't, is that really enough to make any substantial difference for a 9mm?

A 9mm going 1,050-1,100 FPS doesn't receive any real benefit at 1,150-1,200 FPS, so whoopie that you might get an additional +50-75 FPS.

 

I am specifically wondering about a case using underwood XD 90 gr +p.

 

That ammo is already suitable and hot enough.

 

Does Underwood use faster burning powder or slower burning powder? IDK. All things being equal, the G48's longer barrel should give you "faster" velocity.

 

I have both. A pair of 48's plus a 43X. I can't see or tell any discernable difference between the two. I haven't had them under the chrono but I doubt I would be astonished by the results based on playing around with threaded barrels.

The average is likely not even an extra 50 in velocity. I'd be surprised if it were even half that amount.