I have to post this due to a recent thread and because on many boards in general, some people confuse bore and groove diameter.

Bore diameter- If you were to use a traditional way of making a rifle barrel, you would use what is called a rifle drill (go figure) to drill a hole through the barrel from end to end. The diameter of this hole would be considered the 'bore' diameter. The easy way to remember this is that you use a drill to 'bore' holes in things.

Groove diameter- After a barrel is bored, rifling is put in by pushing through a button that expands part of the bore, or a cutter is used to remove metal from the inside to produce the rifling. The distance from the deepest part of a groove on one side of a bore to the deepest part of a groove in the other side of the bore is your 'groove diameter.'

In a 30 caliber rifle, typically, the bore diameter will be .300" and the groove diameter will be .308" but this can vary a tiny bit within a barrel from end to end and from barrel to barrel. A kink in the middle of a barrel can reduce the bore/groove diameter slightly, while cleaning rod wear can increase the bore diameter slightly on a muzzle.

If you want to check the barrel dimensions of a rifle, especially if its a foreign rifle where dimensions tend to vary more, you can slug a barrel. After slugging, the high spots on your slug would represent the grooves and the low spots, the bore.

I posted a bit on slugging awhile back.

http://forum.hunting.net/asppg/tm.as...ugging&#864158

The drill you refer to has no lead, so it bores straight. After boring barrels are reamed to the bore diameter, as the reamer leaves a cleaner hole. Then it is rifled. The hammer forged barrels have an oversized hole, the barrel is placed over a mandril that has the rifling in negative that is reversed, multiple hammers then pound the barrel to fit on the mandrel. [8D]

Good general discription of the post for people whom have asked. One note as you know is that no barrels have a straight rifleing bore in them,some more than most are. None perfect. Thats another reason for the crown to be 90% of the muzzle to helllp being the most accurate as possible as barrels can be. Theres a lot to barrels,accuracy,ect. and it fun to talk about it,and trying to have the most accurate riflee one can have. vangunsmith

[quote]ORIGINAL: vangunsmith

Thats another reason for the crown to be 90% of the muzzle to helllp being the most accurate as possible as barrels can be.


You lost me here . . . . what do you mean by the crown being 90% of the muzzle? Roskoe.

Say WHAT??