Waiting for a couple jobs to finish, so you get to suffer from my boredom.
As background, a .308" bore actually consists of a .300" diameter circle bored through a barrel, and then rifling added which makes the rifling-rifling width a total of .308".
![[Linked Image]](http://www.gunnersden.com/1-rifle-barrel-bore-view.gif)
Now there's been a lot of talk about .224 bullets being bad for 22HP's which have a .228" bore over the long run, because they don't seal the barrel and hot gasses escaping past the bullet will erode the metal. That's a very valid concern...
Except, a .228" barrel is would typically have a main bore of .220", and rifling added that makes it .228" max width from the bottom of one rifling to the bottom of the opposite rifling.
But.. there's this report from 1920 which state that the 22HP bores were actually .226", and they did the same trick with oversized bullets of .228" similar to the .303 caliber bullets out of a 30 caliber barrel they did in the 303 Savage very early on. If that's the case, then the main bore on a 22HP would probably be .218" and the rifling extends it to .226". Which is the same main bore that's on a modern 5.56 which shoots .224 bullets.
-- Horace Kephart, Outing article 1920 introducing the 1920: "Again when they brought out the .22 H. P., they made the bullets .228 for a .226 barrel."My thought is regardless of whether the bore is a .226" or .228" on a 22HP, that a .224" bullet is going to seal that barrel just fine because the rifling is a small portion of the bore surface. So the .224" bullet will be swaged down to .218" or .220" over the majority of the body, and the (relatively) soft copper will be squeezed into the lands to a depth of .228" quite easily.
Am I off? I would still say .224" bullets aren't ideal for the .228 barrels, if nothing else the difference in diameter will change the pressure and velocities you get. But I just don't see it being "bad" for the rifle.
Now the fun part is to dig out my 22HP and slug the barrel to see if it's really .226".
