Have I got this right on bore diameters?

P O Ackley did a test on bullet size and pressure. I do not remember all the details, but roughly: He re-cut a .30 caliber barrel with an 8x57 reamer. Apparently, there was really no pressure deviation as long as the neck and lead were 8mm. The pressure swaged the bullet to .30 caliber size. As for oversized bores, I still don't have a set opinion on that. I have owned quite a few rifles that I shot .308 bullets with great success that had .312 barrels. I would have to say bullet weight and velocity have more to do with some people's gun accuracy problems than a bad barrel.
 
Ever wonder why Kreiger 30 caliber match barrels' .3075" groove diameter is smaller than 30 caliber match bullets' diameters?

Same reason the Brits made their 7.62 NATO match barrels' groove diameter .3065" to shoot arsenal M80 bullets with .3070" diameter.

......

SAAMI specs for 22 Hornet barrels are .217" bore and .222" groove, +.002" for both. Bullet diameter specs are .2245" -.003".
 
Last edited:
OK, bullets are groove diameter, as I thought.

I was wrong on definition of "bore" however (thanks for the info) - I thought bore was one and the same as groove (...was the same as bullet).

But how can bore *not be* then, the same as land diameter? How can "bore" be wider than land diameter?

So the .22 hornet going to .224 in most modern rifles is sorta like Ruger making the mini-thirty with a .308 bore - just an evolution over time due to market expediencies...except that in Ruger's case, the ammo (mostly) didn't follow the new rifle diameter. What about .22 hornet - if you buy .22 hornet loaded ammo that is not labeled as to bullet diameter, which bullets are gonna be in it?
 
Technically, we're all using incorrect semantics, though we all know what we mean. ;)

By SAAMI definition:

"Bore" is the entire interior of the barrel forward of the chamber.

"Lands" are the portion of the interior of the barrel that remains uncut by the rifling.

"Groove/s" refers to rifling.

"Rifling" is grooves formed in the bore.
 
OK, bullets are groove diameter, as I thought.
Click to expand...

Well, yes, in America, usually, with jacketed bullets, mostly.

There was a European school of thought that said the grooves ought to be deep enough to give the metal displaced by the lands someplace to go. Groove diameter greater than bullet diameter. I don't know if they still do that; I find SAAMI specs but not CIP.

Modern American cast bullets are recommended to be slightly larger than groove diameter for a good seal and minimal leading with hard alloys.
 
You must log in or register to reply here.
Back
Top