Proper bullet size?

[jski]

I have a .30 Carbine Blackhawk and have been reloading for it for some time. Lately I ordered some 155 gr GC cast bullets from Montana Bullets Works with a .308 diameter. I measured the cylinder throats; they were all .307. But, I can easily push the bullets thru the chambers with a cleaning rod.

When I try to push a bullet into the forcing cone, it’s immediately stopped and I’d need a hammer to push in further.

Is there any reason to consider next time ordering .309 diameter bullets? I was concerned that the bullets so easily passed thru the cylinder throats.

[Conditor22]

Sometimes cylinder forcing cones/cylinder throats are too small.

How does it shoot and is there any/much leading?

[Rattlesnake Charlie]

Try what you have. Might work fine.

[jski]

It boils down to this: what should the bullet diameter be with respect to the cylinder throat diameter? There seems to be some debate about this.

[mdi]

I think of "easy push through," "drop through", "snug", etc., to be just terms and not really helpful for actual measurements. I think you should measure the cylinder throats and slug the barrel (neither is very difficult). Measure the cylinder throats (pin/plug gauges,expanding ball gauges, etc.) and slug the barrel to make sure the throats are larger than the groove diameter of the barrel. Then size (or purchase) bullets the same diameter as the throats. If the throats are smaller than the grove diameter there is a very good chance of leading, and if the bullets are much larger than the throats, they will be swaged down. I don't know about a debate, just logic; a bullet too small, smaller than the groove diameter of the barrel is apt to lead. If a throat is smaller than the groove diameter, the bullet passing through the throats will be sized down and too small for the groove diameter. I have used this "rule of thumb" for 7 revolvers shooting cast lead...

[jski]

I’m using:
TYPE: FN-GC
ALLOY: Linotype, BHN 22
DIAMETER RANGE: .308"
WEIGHT: 155gr
CALIBER: 308
NOSE TO CRIMP: 0.475”

With the chamber throats measuring .307”, if I were to use something larger than .308” diameter bullets, I’d have trouble getting the cartridges to seat properly in my Blackhawk cylinder.

As for which powder and how much, I’m using 10-11 gr of H110, possibly going as high as 12 gr max.

[Cherokee]

In my 30 Carbine Blackhawk I use .309 size CB, they shoot fine and are very accurate.