revolver cast bullet size

[ageingstudent]

Casting newb question:

I have a model 66-0 and the throats measure .3565-.3570, and a GP100 that the throats measure .3570-.3575. (Slugged and measured with a mic)

1.) Are those sizes pretty common to those guns? I have no frame of reference and am hoping someone here has similar numbers.

2.) Assuming my measurements are reasonable, I haven't bought a sizer yet, but from what I read I should be looking at sizing/casting to .358 right?

3.) .358 won't be too tight for my old 66 will it?

Thanks

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[Tilos]

I have lapped cylinder throats to remove the variation and standardize them, to try and improve accuracy.
You can lap the forcing cone too.
Your gun tweak's are endless...
I always buy cast bullets big and have many Lee push thru sizing dies of different sizes to resize bullets for a particular gun.
I have tested/shot groups from one cylinder chamber to determine which chamber is the most accurate.
If I were you, I'd size the bullets to the smallest throat and call it good.
If the bullets are too big the throats will lead.

That said, I have found the restriction in the barrel, where it threads into the frame, to affect the accuracy more than throat diameters.
That too, can be lapped out, see endless tweaks,

 

[ageingstudent]

Thanks, I've been experimenting with hitek coated bullets in 358 with pretty good results. I was using some traditionally lubed commercial .358 in the 66 and the leading was minimal. Still don't like the messy traditional lube in my dies and smokey rounds at the range. Wanted to make sure I am not going to order a sizer too big for the 66 at .358. I don't think leading is going to be a problem with coated bullets unless something is way out of whack. I've been lucky not to have to tweak my 6 shooters. Accuracy has been great out of both.

 

[Tilos]

I've switched coated too, and won't be going back to lubed either.
I have 2k cast/lubed bullets loaded that I have not shot because of the mess they make of my guns/brass.
I haven't tumbled any brass since switching, just wash the stuff that ends up on the ground.
I've shot some swagged/coated bullets, that were soft, without any problems or leading.
Another plus for coated is I buy bullets with no lube groove, so I can use a bullet feeder die.

 

[noylj]

Best is you shoot them and see if they lead.
In general, you want bullets that are a snug slip-fit in the cylinder's throats and at least 0.001" over the actual barrel groove diameter.
There are a lot of old revolvers out there with 0.356-0.357" throats and 0.358" groove diameter--these tend to be jacketed-only guns. They would "sort-of" work with very soft bullets (6-9 BHN), but today, 15 BHN is almost a minimum if buying commercial bullets.