I shoot exactly the same load from a 4" M66 that I shoot in a 22" rifle. The M66 clocks around 1300 fps and the rifle around 1750 fps. The pressure is the same, except for BC gap, so pressure is only one thing that will affect velocity, with barrel length being another thing and with still other things affecting velocity too.

In those same loads, .38 Special BTW, I use a 12 BHN 358429 and don't get any leading at either velocity. They are sized at .3585", or basically as cast size.

Considering a .38 Super and a .38 Special will both shoot a 125 gr bullet at 1200+ fps, it's going to take more than that to be a magnum. A .38/44 will get around 1150 fps with a 158 gr bullet. I think too many are too used to modern loads that don't perform like a magnum should.