What sizing diameter? .308", .309", or .310"? - .30 Carbine Blackhawk

[jski]

I'm ordering hard cast, GC bullets for my .30 Carbine Blackhawk. Montana Bullet Works just asked a question: What sizing diameter? .308", .309", or .310"?

Suggestions?

The bore is .308. Is there a reason to oversize (slightly) the bullet?

 

[theleo]

Check what your cylinder throats are, if they are .310-.309 I'd order to match the throats. If your throats are below .308 I wouldn't bother trying lead. The throats will effectively sage the bullets down before they get to the barrel. The rule with lead bullets is .001-.002 over the bore diameter for best results.

 

[ReloaderFred]

My .30 Carbine Blackhawk was made in 2014, and when I measured the chamber throats, a .308" pin gauge would just slide through, but a .309" pin gauge wouldn't. The .309" gauge would just start into the chamber throat, but stopped. I sized all my bullets at .309" to match the throats, but I haven't had a chance to get to the range yet to do any serious testing with them.

If I were you, and you don't have access to pin gauges, then I'd take a .308" diameter bullet and see how it fits the chamber mouths. If it's a sloppy fit, then I'd go with at least .309" diameter bullets, but if it's a snug fit, then .308".

Hope this helps.

Fred

 

[GLOOB]

I'd go with a small order of 309 or even 310 to start, and a Lee 308 bullet sizer. You can make bullets smaller, and you can make sizers larger. Can't do it the other way around.

Personally, I want the biggest bullet that chambers. Throat matters, and the throat needs to be slightly bigger than the bore. But I wouldn't be too meticulous about fitting the bullets to the throats, even. If you can fit a larger bullet in the chamber/leade, it'll shoot fine, too. It doesn't take too much force to size a cast bullet, whether you do it by press or by shooting it.

 

[mhblaw]

+ 1 for GLOOB. I found a cast 125 gr. SWC in .312 that I use in 32-20 and 327 Fed. Mag. I use a Lee sizer to bring it down to .309 for my 30 Carbine BH. Works just fine.