Are the cylinders of most .38 revolvers an 1/8 inch shorter than the cylinders of .357 revolvers? ( within the same manufacturer) I replaced the cylinder in my 642-1 with a titanium cylinder capable of chambering .357. And no, I won't ever shoot .357 in it. My point....unless the revolver you're looking at has a cylinder an 1/8 inch shorter then the bullet from the .38 cartridge still has to travel further before reaching the forcing cone.

I've never gone around with calipers measuring cylinders on .38 revolvers.