.38 from .357 chamber velocity question

[Ron3]

You guys who have read/run chronos:

Will the same .38 load run slower from a .357 chamber than a .38 chamber, typically?

From reading others' results it seems a given .38 load loses 50-100 fps when fired from a .357 chamber. (Given same barrel lenghts)

True or false?

[williejc]

I've seen no published data on loss of velocity of .38 Spl's fired in .357 chambers. Some say that some loss of accuracy may occur because the bullet has 1/10 inch more travel in the longer cylinder. I've been loading both calibers and firing both in .357 cylinders for almost 50 years and have not observed accuracy loss. The great majority of my reloading has been with cast bullets, and I have been able to match bullet diameter to accommodate chamber/bore diameter and thus achieved excellent accuracy. With the same load, lead bullets will achieve higher velocity than jacketed because lead has a lower friction coefficient.

I have seen chronograph data with the same round fired in different revolvers of the same barrel length, and there was variation from revolver to revolver--whether or not they were the same brand. Cylinder gap--distance between rear of barrel and front of cylinder--affects velocity. More gas is lost as the gap widens. My opinion as an advanced hobbyist and reloader is that velocity loss in the .38 spl fired in .357 cylinders is insignificant if it occurs at all.

[CAVDOC]

Any difference has to be marginal - in a s&w for instance the cylinder length of a k frame 38,357,even 22 are all the same

[Ron3]

Thanks for the information..I had wondered about this for quite some time.

Ron3

[TomMcC]

I haven't run them through a chrono, but we're talking a 1/10 of an inch here.

[TiroFijo]

False. I have run the same ammo from several 38 and 357 revolvers, and results are all over the place, the barrel/cylinder gap and chamber, forcing cone, etc. variations are far more important. In average, the velocity should be zilch to minimal.