"Ballistics" is interesting stuff eh ..
But .. warning warning this is just an opinion .. but I doubt that there is much practical terminal performance difference between a .38"S&W Special fired from a 2 inch snubby revolver and a decent .38 S&W fired from a 4 inch antique revolver barrel.
I was thinking about 'lead wadcutters' loaded backwards as expanding loads for 'bowling pin' matches etc. - Of course there is a very obvious direct CONFLICT between Expansion and Penetration. - Bigger Diameter > More Drag > Less Penetration.
Around 1985 / 1986, PMC would adapt a design by Abe Flatau (designer of the ring-airfoil and steel nose Guilford HP pistol bullet) in their own line of "Ultramag" cartridges in .38spl and .44spl. The first .38spl projectiles were true hollow cylindrical bullets with a tapered nose and plastic obturating base. These were made of brass (66 grains) and had decent, yet limited enhanced penetration abilities at 1,500fps. These were effective against soft body armor, but not against steel plate, or hard metals. The federal law restricting pistol-caliber AP bullets would soon follow in August, 1986, and so PMC would switch their now restricted brass bullets over to 100% copper. Using copper would more or less defeat the intended purpose of real enhanced penetration, and these copper tubular bullets would continue on as a novelty of sorts for a few years until PMC gave up on the concept altogether. The initial brass bullets were only produced for a year or so in .38spl, and are fairly rare today as collector’s items. The copper versions are much more common, and full boxes of .38spl can be found via auction websites at times for anywhere from $40 to $75, with the .44spl boxes being worth closer to $100.