I understand that overbore means a cartridge with a grossly large powder charge for the bullet diameter or weight, but what is there a formula for determining this? A ratio of bullet diameter to case capacity? What's the correct definition or method of measuring this?

Also, along the same lines of thought, would there be a way to determine the ideal charge weight or case capacity for a given bullet size/diameter?

I would like to bring your attention to 24 Hour Campfire forum. Dr. Ken Howell resides there, with a forum for asking him questions. He'll be glad to answer this question. He's given it once there, perhaps you may decide to do a search for it instead. ~~~Suluuq

www.24hourcampfire.com

Over-bore capacity is a relative term used in reference to the canister grade powder(s) available which can provide a charge that fills the case without raising pressures above the safe recommended levels (ie 65,000 PSI). With the available powders of today, the 25-06, for example, can be: at, under and over-bore capacity. If you were to use Alliant Unique in the 25-06, you would have a situation where the case is dangerously over-bore capacity for the powder.

If you select powders like IMR-4831 or R-19, the 25-06 case falls into the �at� bore capacity. At the same time, if you choose a powder like 50 BMG, you would be at the extreme opposite end of the spectrum, with a case that is Under bore capacity. Offhand, I can�t think of any cartridges today that are �over-bore� capacity for any of the powders available on the market.

Turok

Missed one.

The 'correct' charge weight is also a relative term based on the desired results. If you want efficiency then the 30-30 is probably your best bet. But if you want performance at any cost, then you would set the parameters to more powder and a much larger case.

Pressure is also another consideration when referring to the correct powder weight. Do you want to run at 50,000 PSI or 65,000 PSI? If you want the lower pressure, but still have the same velocity you must move to a larger case. If you choose the smaller case, you must run at a higher pressure to obtain the same velocity.

So, yes there is a method of determining the correct powder charge for a given case and bullet weight/diameter, but it involves more math than I can handle. Programs such as QuickLoad and the like can quickly determine this given the dimensions of the case and bullet weight. But like I stated earlier, these are all relative to what you want.

Turok

Turok

GLC, I saw this definition on another board, FWIW
"Overbore is when case capacity (in grains water) is greater than bore diameter squared times 1000"
Regards, Curley

Overbore is a 338 Lapua necked down to .257 and filled up with IMR 7828 behind a 75 grain VMAX!! GHD

Two words, Weatherby Magnum..

Thanks for all the responses.

GLC