Measure RBH throat?

[Doctor Sam]

One of you guys tell me how to measure the throat on a Ruger BH.  My caliper won't fit and I don't own anything else.  
0.454" bullets are a slip fit in all the cylinders that mike anywhere from 0.453" to 0.457".
I'v been using store bought cast 250g RNFP from Wayne Doudna, LTD Custom Cast Bullets, since he sells them for $38/1000.  I'm not going to cast them when I can buy them for that price.  Maybe he could send a few as cast, then lubed with liquid Alox, might fill up these holes.
It would be interesting to know the diameter of the throat.
Many thanks.
Dr. Sam

[Iowegan]

Doc, Looks like your throats are a bit generous. The ideal throat diameter for jacketed bullets is .4515" and .4525" for lead bullets. Your gun will probably shoot just fine with good accuracy. You will experience some lead fouling on the cylinder face, forcing cone, and maybe some gap spitting. It cleans up so don't worry about it.

The bore diameter is more important when trying to determine what diameter bullets to use. The best match is when the lead bullet is .002" larger than bore diameter. This insures a good gas seal in the bore and minimizes fouling. If you try to use a larger diameter based on your throats, you will get excessive fouling in the bore and poor accuracy.

[Doctor Sam]

Bore is 0.451".  Shoots better with 0.454" cast bullets than with 0.452".  According to Dave Scovill, a softer alloy will seal the cylinder throats and shoot more accurately than the hard cast bullets.  He used a 1:16 mix.  May see if I can find some.
Thanks.