What diameter to size .30 cal. bullets

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  • Last Post 10 October 2022
Slug Gun posted this 10 May 2021

I have a new barrel that is .300” / .308” (10” twist) and was wondering if I should size the bullets at .308” or .309” or maybe even .310” to help with a good gas seal. The bullets are from a NOE 311-206-RN mold with a gas check for a .30-06 cartridge. I did a search and found nothing in the archives. 

THANKS for your suggestions.

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Spindrift posted this 10 May 2021

My default .30- cal size, is .310- wether the bullets are lubed, or coated. The Marlin 30/30 micro-groove gets,.311

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RicinYakima posted this 10 May 2021

In a fired case, what is the largest bullet that will fit in the neck? That is where I start, FWIW. 

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Bud Hyett posted this 11 May 2021

Good thoughts above; especially Ric's thought to start with a fired case. I start at .310 for both commercial rifles and military. Sometimes go to .311 for military after experimenting.

You'll need to experiment with loads and hardness to find what sizing works. A good source of data is the match results for the Traditional or Military competition. See what others are shooting and start there. 

Farm boy from Illinois, living in the magical Pacific Northwest

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John Carlson posted this 11 May 2021

NOE occasionally changes the nomenclature on their molds, I believe I have the same one but called a 311202.  It works well in newer barrels with tighter chambers.  I also have a 314206, slightly larger version of the same bullet.  It works better in rifles with worn chambers. They also make a 312 version.   As Ric says, size the driving bands to fit the throat.

John Carlson. CBA Director of Military Competition.

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Rich/WIS posted this 12 May 2021

.310 is my default size,  works in a number of different 30 cal barrels.

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Tombstone posted this 20 September 2022

I'm Just A Little Confused. Am I correct in thinking that you use a sizer for your cast bullet that is .001 to .002 larger than the bullet size you cast. For instance, a .38 caliber pistol bullet is .358 in diameter, so it should be sized using a sizing die .001 to .002 larger? 

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JeffinNZ posted this 21 September 2022

Like Ric said.

I shoot .312 in my .30-30 Husky.

Cheers from New Zealand

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Boschloper posted this 21 September 2022

I find RicinYakima’s comment very interesting. Sizing to a fired case means you are sizing to the chamber neck diameter (less case neck thickness and the little bit the case contracts after firing), and not groove diameter.  I am currently shooting 311291 in three .30-06’s and two .30-30’s, all sized .3092.  I need to measure some fired cases. This could mean gun specific sizing. Is the goal to be larger than groove diameter but small enough to release from the case neck?

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.22-10-45 posted this 21 September 2022

The late Dennis Marshal advocated sizing bullet diameter to match throat dia. Minus .0005". For hunting a full .001"under is safer.  In my  Llilja barrel Al Story Borchardt .30-40 krag, throat dia. Is .310 and that is what I size to.

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RicinYakima posted this 21 September 2022

I normally have 50 cases for each rifle, plinkers, and 200 for match rifles all of the same lot. Yes it means gun specific sizing. Unlike Mike the Duke, I don't require every caliber to fit into every rifle that I own of that caliber. . 

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mashburn posted this 21 September 2022

Nobody has answered your question as of now. Your bullet will probably come out of your mold larger that .311. Even if is not much over size,they are telling you to size the bullet down to .309 or .310 or .311, The other information given was to size to fit the throat of your rifle. I myself in this type of rifle size .002 over with lubed bullets, which I don't shoot anymore, and I go .001 over on powder coated bullets.

Mashburn

David a. Cogburn

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Aaron posted this 21 September 2022

Precisely what mashburn has said above. Your cast bullet will also drop from the mold with different diameters as alloy changes but in all cases, size the oversize bullet down to whatever final size you determine works best in your rifle. Since I do not compete with these to spare our senior members embarrassment cool, I size my 30 caliber bullets to .309 and keep the final velocity appropriate to the alloy.

Custom molds can be made to drop the bullet from the mold at final size (309 perhaps) using a specified alloy. They do not have to be sized (reduced in size) but instead go through a size die of 310 to apply lube to them. They could also be pan lubed.

My 45-70 bullets drop from a custom mold at final size in 20:1 alloy.

Short answer: I size to .309 for 30 caliber.

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mashburn posted this 21 September 2022

Hello Spindrift,

I note that you have changed the dimensions of your powder coated bullets from .001 to ,002. I'm sure you have good reaso for this. Also, are you still letting the PC bullets jump a little instead of shoving them up in the throat?

Mashburn

David a. Cogburn

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Barn-Dweller posted this 10 October 2022

For my 30 cal stuff I size to .310  if I remember right the cast book manual told me .309 for 30 cal but I round much more accuracy at .310  I am shooting powder coated bullets.

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