Last time I chronographed factory .357 Magnum ammo through various revolvers, I used Federal American Eagle JSP. While I didn't think to write down the exact numbers, I was averaging ~1150 fps from my 2 1/2" S&W M66, ~1200 fps from my 3" S&W M13, ~1300 fps from my 4" S&W M28, and slightly under 1350 fps from my 5" S&W M27. While I didn't chrono as much of it, I got very similar number from Remington HTP 158 gr SJHP which is my chosen self-defense .357 Magnum loading. These Federal and Remington loadings are advertised at 1240 fps and 1235 fps respectively and while Federal does not specify a barrel length, Remington states a 4" vented test barrel for their advertised velocities.