What is the ideal bullet size for a bore?

[20nickels]

I have a few com bloc rifles that slug at .312 What is the Ideal jacketed bullet size for these bores? Something tells me the answer is obvious but what is your take? Slightly oversize? Slightly undersized?

[alfloyd]

With J-slugs, I would shoot .312 dia bullets.

Just the way I do it.

Lafaun

[Reload3006]

+1 With alfloyd shoot bore size. you probably can get by a .001 under or maybe .0005 over.

[BT Sniper]

There is an exellent question! What is the ideal bullet size for a given bore?

I too would go for a .3120 bullet in a .3120 bore.

I agree with 3006 as far as tollerences, maybe a half thou more on the plus side actually but I need to test a bit more.

I am certain I have shot some .309 bullets in a 30 cal bore and some .225 in a 22 but I obviosly don't recommend shooting this much oversized. Many of the match bullets will have a "driving band" that is a few tenths over standard bullet diameters.

I hope to experiment a bit more as I get additional 30 cal dies put together.

See if I can try some bullet diameters from .3070-.3090 with everything in between.

It will be interesting to see what others have to say and offer.

Good shooting, Keep it safe!

BT

[20nickels]

I was told by somebody whose opinion I respect that .312 would be a bit plump for that bore but that didn't seem quite right to me even though .310 and .311 bullets are very common for com bloc rifles. Is this CYA policy from the MFG's maybe trying to prevent overpressure?

[45 2.1]

A lot of things effect that perfect boolit size, like: throat size, chamber neck size, load intensity, boolit hardness and design, etc. Everybody seems to do things differently. You get out of it what you put in it.

[MIBULLETS]

Exactly what 45 2.1 said, when you slug the bore you can only tell what the tightest point of the bore is.

Many benchrest shooters will shoot bullets over bore diameter, especially at the base of the bullet. I believe most agree that dead on GROOVE diameter, not bore diameter up to .001" over will shoot the best. Going undersize can lead to the bullet very slightly tipping in the bore before possiblly slugging up.

I know this is not a benchrest gun but the same principles apply.

[BT Sniper]

Yep groove diameter being the widest point!

[Reload3006]

lol yea groove diameter Semantics but it was what i was referring to guess with out pictures etc its best to be more careful on descriptions. If you slug your bore its the biggest part of the slug you measure shoot that size to -.001 jacketed +.0005 jacketed +.001 maybe .002 lead.

[DukeInFlorida]

Exactly.

The measurement you take is the largest diameter you can measure on your slug.

lol yea groove diameter Semantics but it was what i was referring to guess with out pictures etc its best to be more careful on descriptions. If you slug your bore its the biggest part of the slug you measure shoot that size to -.001 jacketed +.0005 jacketed +.001 maybe .002 lead.

[20nickels]

I know this is not a benchrest gun but the same principles apply.

Actually I got ahold of a stripped Mosin rec. and a 7 lb machine gun barrel in 7.62x54r. It is my #1 reason for this thread. Benchrest might be a strong word for it when I'm done but the varmints won't like it one bit. Tks for all the very good replies. The CB swaging forum holds knowledge I can't find anywhere else on the web.