http://www.ballisticsbytheinch.com/gaptests.html
In this set of tests by Ballistics By The Inch, they rigged an Uberti in .357Mag so that not only could the barrel length be altered, but also the cylinder gap between .006, .001" and "zero gap", with shims.
I do have some issues with their methodology:
1) They didn't test .38s in .38Spl chambers - everything was done on a .357. That might matter some.
2) While their selection of .38 and 38+P ammo was excellent, they have basically ZERO high-performance 357 ammo. The closest they come is Federal's 158gr load and even that's pretty wimpy. All the rest are either downloaded (Cor-Bon DPX isn't full power) or practice grade. There's not a single high-performance 125gr, even from a major manufacturer. Buffalo Bore was tested in 38 and 38+P, not present in 357. Very annoying.
3) There's too many "outlier cases" where in one particular load and barrel length, you'll get a "flyer" - often in places that don't make any sense at all. Examples include Cor-Bon's 38+P 125gr at the 16" point, Buffalo Bore 38+P 125gr at 3" where .006" does well only at 3", Cor-Bon 357 DPX at 5" (*** happened there?) and more. The most serious is the Black Hills 38 Long Colt data at 13" - that spike is just not possible. Damned if I know what happened, but, something did.
On the plus side, their data for the legendary BB 158+P load starts in the very high 900 range from a 2":
http://www.ballisticsbytheinch.com/buffalobore3.html
Italian barrels aren't as good for speed as Ruger and later-model S&W wheelgun barrels, so with a better gun than that Uberti you should see BB's claimed 1,000fps from a 2" barrel. We also see a huge jump of about 75fps from the 2" to 3" barrel in this load - out of a Ruger or recent-vintage S&W we might see 100fps. Oh, and 38Spl chambers might make the extra difference to an honest 2" barrel 1,000fps load.
Those issues aside, some clear trends emerge:
a) The difference between a .001" gap and .006" gap isn't much, but in a 2" barrel with 38+P ammo the 30fps or so average difference may be enough to cause a round to expand, or not.
b) The difference between 2" and 3" barrel velocities across the various combat rounds is often very high - up around 100fps in some cases. THAT is enough to affect expansion, I guarandamntee it. All of the makers ought to be doing more 3" guns, and the 3" Ruger SP101 ought to be selling better than it is. That extra inch of barrel will make a difference in concealment only if you're doing pocket carry - for anything else (ankle, shoulder, IWB, "belly band", jacket pocket or fanny pack) a 3" version will be only fractionally harder to conceal in most cases.
I have long been a proponent of small gaps in snubby revolvers, and as far as I'm concerned this data supports that concept. I've also been pointing out that 3" ballistics are usually better than 2" by a useful margin and again, I see a lot of evidence in favor of that idea too.
In this set of tests by Ballistics By The Inch, they rigged an Uberti in .357Mag so that not only could the barrel length be altered, but also the cylinder gap between .006, .001" and "zero gap", with shims.
I do have some issues with their methodology:
1) They didn't test .38s in .38Spl chambers - everything was done on a .357. That might matter some.
2) While their selection of .38 and 38+P ammo was excellent, they have basically ZERO high-performance 357 ammo. The closest they come is Federal's 158gr load and even that's pretty wimpy. All the rest are either downloaded (Cor-Bon DPX isn't full power) or practice grade. There's not a single high-performance 125gr, even from a major manufacturer. Buffalo Bore was tested in 38 and 38+P, not present in 357. Very annoying.
3) There's too many "outlier cases" where in one particular load and barrel length, you'll get a "flyer" - often in places that don't make any sense at all. Examples include Cor-Bon's 38+P 125gr at the 16" point, Buffalo Bore 38+P 125gr at 3" where .006" does well only at 3", Cor-Bon 357 DPX at 5" (*** happened there?) and more. The most serious is the Black Hills 38 Long Colt data at 13" - that spike is just not possible. Damned if I know what happened, but, something did.
On the plus side, their data for the legendary BB 158+P load starts in the very high 900 range from a 2":
http://www.ballisticsbytheinch.com/buffalobore3.html
Italian barrels aren't as good for speed as Ruger and later-model S&W wheelgun barrels, so with a better gun than that Uberti you should see BB's claimed 1,000fps from a 2" barrel. We also see a huge jump of about 75fps from the 2" to 3" barrel in this load - out of a Ruger or recent-vintage S&W we might see 100fps. Oh, and 38Spl chambers might make the extra difference to an honest 2" barrel 1,000fps load.
Those issues aside, some clear trends emerge:
a) The difference between a .001" gap and .006" gap isn't much, but in a 2" barrel with 38+P ammo the 30fps or so average difference may be enough to cause a round to expand, or not.
b) The difference between 2" and 3" barrel velocities across the various combat rounds is often very high - up around 100fps in some cases. THAT is enough to affect expansion, I guarandamntee it. All of the makers ought to be doing more 3" guns, and the 3" Ruger SP101 ought to be selling better than it is. That extra inch of barrel will make a difference in concealment only if you're doing pocket carry - for anything else (ankle, shoulder, IWB, "belly band", jacket pocket or fanny pack) a 3" version will be only fractionally harder to conceal in most cases.
I have long been a proponent of small gaps in snubby revolvers, and as far as I'm concerned this data supports that concept. I've also been pointing out that 3" ballistics are usually better than 2" by a useful margin and again, I see a lot of evidence in favor of that idea too.
