Ruger Blackhawk 30 Carbine Groove Diameter?

[DougGuy]

If you have slugged a 30 Carbine Blackhawk and done it correctly (dead soft lead ball or egg sinker, and measured with a micrometer not calipers), what were your groove diameter measurements?

[Outpost75]

My 1977 date of manufacture Ruger is .308 groove by micrometer measured lead slug with bore diameter .3005" as near as I can determine, a .300 pin enters with no felt resistance and a .301 won't start. Cylinder throats are .3095-.310" reasonably uniform, which is why you've never received the cylinder from me. Gun shoots more accurately at 100 yards than my Inland USGI M1 carbine, so am leaving it alone.

Most accurate load is Hornady .309" 90-grain XTP with 7.4 grains of AutoComp, 1450 fps. Nearly as good is Accurate 31-100T cast 13-15 BHN and sized .310" with the same charge, 1520 fps. No GC. No leading.

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Most accurate single-action revolver I own!