Help with 30 caliber

[whitesquirrel44]

Could someone explain 30 caliber to me? Looking at barrel blanks, they are listed as 30 caliber but don't give the actual diameter. I know from reloading that you use .308 for jacketted bullets and .309 for lead bullets. I know that most 30 caliber rounds like 308 Win and 30-06 are .308 but others like 7.62x54R is listed as .310 and 7.62x39 is listed as .311. I bought some projectiles to reload 7.62x39 that are 123gn .310 and I was given some projectiles for reloading that are 180gn .310. Are these for loading 7.62x54R only. Can the 123gn be used for 7.62x39? Is .001 too small to be accurate? Can the 180gn be used for a 30-06? Is .002 too much? Weaponeer is selling .308 military surplus barrels to use for a 7.62x25 home gunsmithing contest, but the 7.62x25 has a diameter of .309. Can I buy a 30 caliber barrel blank for 7.62x39 round or will diameter of the barrel be too small?

I guess my real question is what tolerance if any for jacketted bullets do I have between barrel and bullet for both oversized bullets and undersized bullets?

I know some of these questions are for reloading but I didn't want to post it twice.

Thanks

 

[rcmodel]

In the U.S.A.:
.30 caliber is .308".
You shoot .308" jacketed bullets in them.

.311" is .303 or 7.65MM.


Foreign 7.62 can be anything they want them to be it seems. And even then, they are not always that.

You can't use 180gn .310" jacketed bullets in a 30-06.
Well, I suppose you can, but you shouldn't!

You can use the 123gn .310 bullets in .308 bore 7.62x39 rifles.
Ruger Mini-30's have .308" bores, but can handle com-block mil-sup ammo safely.

The only way to really know what bore size you have in a mil-sup rifle is to slug the bore and measure it.

Most barrel makers make .308" .30 caliber barrels, as well as .311" 7.65MM barrel blanks.

rcmodel

 

[Jim K]

A rifled barrel blank has (or should have) three pieces of information - bore diameter, groove diameter and twist rate.

A blank designated as .30 caliber is assumed to have the standard .30 bore and groove of .300"/.308" (within normal tolerances).

7.62 NATO, or 7.62x51 (U.S. developed) is a .30 caliber; other bullets designated as 7.62mm may vary.

Jim