Sizing for the .30 cal.

[fuzybum]

I'm just getting started in casting and I want to size all my bullets. The book says to size to .308 but someone told me to size .309. I'll be working up bullets for a carbine, 30-30, and30-06. Would like any suggestions and advice. thanks

Information

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[jimb16]

I suggest slugging the barrels. Then go .001 over. With cast, I normally go .309 with my .308s.

[Kirk]

I presume you mean cast bullets. If so, yes, sizing a cast bullet .001" over groove diameter is a standard practice. It ensures the bore is sealed & that the shank of the bullet is in full contcat with the grooves; it stops gas blow by. Slugging a bore means pushing a small, soft piece or lead (00 buckshot flattened so it starts over .31") through the bore & then measuring it. Unless your bores are worn, .309" is a safe bet but you won't know for sure unless you slug the bore. The Lee sizer die works great, fits ina standard press & the Lee Liquid Alox is an excellent lube. The sizer seats gas checks, too.

[Bill H]

Assuming your groove diameter is .308, then .309 makes sense.

I have fired lots of cast bullets in one of my 03s, and found good accuracy shooting them as cast, lubricating by hand. Don't know what the diameter was, did not have a micrometer way back then. The use of a Lyman sizer sure speeded up the process, but I do not remember it improving accuracy.

As long as the bullets are not undersize for the bore, the exact diameter does not seem to be super critical.

[Larry Gibson]

Most of us with considerable experience have found a .310-.311" sized cast bullet most often shoots best in most .308-.309 barrels. It is actually the throat you want the bullet sized to. The old ".001" over groove depth" was/is a good place to start but it's not where the best accuracy generally is if your bullet drops at .311"+. If your bullet drops at .309" then go with that.

Larry Gibson

[Bob S]

It is actually the throat you want the bullet sized to.
Larry Gibson

+1

Resp'y,
Bob S.

[Dollar Bill]

Right on the money, Larry. That applies to revolvers also. Slug the throat if you want best accuracy.

[NuJudge]

Do not use bullets so large the assembled cartridge will not fit in your chamber. I have had rifles with groove diameters so large that the case neck with inserted bullet would not fit in the chamber neck.

Also, for a semi-auto, do not have bullets thrust into the rifling by the bolt closing. I would worry about out-of-battery explosions. For a bolt-action, I usually assemble the cartridge such that the bullet is lightly engraved by the rifling.

In general, a bullet sized to fit the throat is what you want.