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My take on "overbore" is simply when the amount of barrel needed to effectively burn a case-full of powder is beyond the benefits of extra velocity.
I hear people say a 7mm RUM or STW with a 22" barrel on it has the same or less energy at the muzze than the 7mm Win Mag.
If that's true, it makes me think of other calibers it may also be true for.
358 STA vs Norma, 375 Ackley vs H&H, 416 Rem vs Taylor.
Do all of these full-size cases need 26 inches in order to realize significant gains over their shorter counterparts?
When you're planning on a short barrel does it make more sense to go with the shorter case?
Seems like the Taylor, for instance, can acheive 2400 fps from a 400gr bullet. The Rem Mag can do a little more, but isn't that mostly data from a longer barrel? And what of the Taylor with 26 inches?
 

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I'm not sure, but I thought overbore was when you had a case too big to fill to capacity without exceeding pressure limits. With the slow powders availible there arent many that fall in that category. I dont think those cases need 26" barrels to get any real benefit velocity wise. Charlie sisk did some testing of different barrel lengths on different cartridges, and he posted his results over on 24hourcampfire.

http://www.24hourcampfire.com/ubbth...r=88566&page=1&view=collapsed&sb=5&o=&fpart=1
 

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With modern powders, you need some serious case to bore ratio before you get into the "overbore" condition. I can't think of any big bore that is overbore.

The 416 Taylor needs a 26" barrel to push a 400 gr bullet 2400 fps, the 416 rem can do it in a 22" tube.

The 358 STA will do it's thing in a 24" tube, same with the 375 Ackley.
 
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