.357 bore and groove diameter

Catpop · Jul 26, 2017

Am I correct in reading the .357 magnum saami specs of a .346 bore diameter and a .355 groove diameter?

The saami chart also indicates a lead boolit of .359 (max I presume). The difference between .359 and .355 is .004 indicating .004 is a lead boolit correctly oversized for a .357 bore.
Am I reading this correctly?

Old News: I'm just curious as my 1973 .357 Ruger Blackhawk Leadmaster has a bore of .347+ (pin gage, don't have a .348 to try yet) and slugs out at .3583 with a micrometer. That's .0033 over spec. indicating I need a .3616 lead boolits to correctly fit my blackhawk.

Am I reading this correctly? Please correct me if I'm wrong.

Dave T · Jul 27, 2017

For 50 years now I have believed, understood, read and been told the grove diameter for the 357 Magnum is in fact .357". The exception was always Colts which supposedly had .355" to .356" groove diameters. The size (diameter) of cast alloy bullets you should use is more dependent on the mouth of your revolver's chambers. In those same 50 years I've learned to fit the bullets to the chamber mouths, not the barrel.

Dave

RKRCPA · Jul 27, 2017

My understanding is, based upon your barrel slugging .3583, the proper bullet size would be .358. Of course, to get the benefit of a bullet that size you will need throats of .3585.

murf · Jul 27, 2017

.359" minus .003" for the bullet. .346" plus .004" for the bore diameter. .355" plus .004" for the groove diameter. you can mix and match as long as you stay in bounds!

murf

murf · Jul 27, 2017

go with dave t when choosing bullet diameters for your pistol. fit the cylinder throat, not the barrel groove diameter on revolvers.

murf

.357 bore and groove diameter

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