357, 358 or other for 38/357 cast?

[SSGOldfart]

I size mine to .358 for my Ruger Black Hawk in 357 Mag

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Same here.

[murf205]

I slug the barrel for the groove size and check to see if that size passes through the cylinder throats. If it does, then I size to the cylinder throats. If it doesn't, then the cylinder throats need to be made larger. Just enough to be about .002 larger than the groove size.
I have been lucky in that all my revolvers have groove dimensions that are slightly smaller than the cylinder throats on any given gun. They will all chamber .358 boolits even though a couple of them have throats slightly smaller than that. They still shoot well because the boolit fits the barrel well even after being sized down by the cylinder throats.
No leading and good accuracy this way.

Outpost 75 is correct about the pin gauges. I don't have pin gauges so I use a bullet/boolit of known size(I do have micrometers) and see how it fits the cylinder throats.
It is a cheap way to find out but it works for me.

I did'nt realize just how reasonable pin gages wer or how much they helped the process until I bought some for my revolvers. IIRC I paid something like $3 each for mine and you don't have to buy an entire set to do what we want to do.
I have been getting by with the same thing you are with regards to my 686. It has .357 throats and barrel but it shoots 180gr Cast Performance .358 GC boolits really well-probably because of the gas check.

[44magLeo]

I don't have pin gauges. I use cast boolits.
I use them as cast. With a bit of oil in each throat I push one boolit through each throat. Measure. This gives me the sizes of the throats.
Using the largest throat I size a few boolits. I then load them in cases. Try these dummy rounds in all the chambers. If they fit the chamber I size to that diameter. I get no leading and very fine accuracy.
I also slug the barrel and have been lucky that the bore was always a few thou under throat dia. In my Dan Wesson 357 it likes them at 358.
My Ruger Redhawk and SBH like them at .430.
I load cast in some of my rifles. These I try to fit the boolit to throat diameter or as close as I can and still chamber.
In my Marlin 1894 44 Mag this gets boolits to .432. In the Mosin Nagant that's about .315.
Both shoot them well.
Leo

[bob208]

when I started loading and casting in 72 I bought a .357 h&i die still using it so it could be .358 by now. have used the bullets in rugers, colts, smiths and others with no problems. as long as the bullets shot as good as I can hold and don't lead I call it good. I don't do all this pin measuring.

[murf205]

Pin gage measuring is not a cure for all diseases but it gives a good starting point for a new gun that you are going to order a mold for. I am a habitual gun trader and it gives me a starting point for a gun that I might not have a boolit to measure with.