Bullet / bore / groove fit

[cuslog]

So I've been primarily a cast bullet / target shooter all my life. In that "game", bullets are typically .001 ~ .002 (or even more) over groove dia. in the barrel. But this is typically a lower pressure, more forgiving "game".
Now, thinking about jacketed bullets and higher pressure cartridges, what would be acceptable "fit tolerances". I'm thinking that a bullet fit that's over groove diameter may not be as forgiving as in the case of a cast lead bullet.

 

[bearhunter]

Again, that really depends on the type of bullets you will be shooting.

Match bullets usually have thinner jackets, which allow the bullets to obturate into the grooves better.

Hunting bullets will have thicker jackets that don't obturate quite as well.

I like to match bore diameter with bullet diameter if possible.

With most of today's CNC manufactured or hammer forged barrels, as well as custom barrels, bore diameters are usually extremely consistent from one barrel to the next and the same goes for bullet diameters.

Back in the day, bullet bases were always open, to expose the lead cores. Even the early boat tail bullets were constructed that way.

The reason for this was to apply pressure to the exposed lead and force it to push against the jacke material and make it obturate into the grooves for better accuracy. Of course todays consistent and tight tolerances don't require such extremes.

 

[guntech]

An over size bullet is swagged to the correct size within it's length of travel in the barrel. Nothing to worry about.

 

[bearhunter]

An over size bullet is swagged to the correct size within it's length of travel in the barrel. Nothing to worry about.

Not if it's to small, which can cause offset when entering the leade

 

[guntech]

Quote Originally Posted by guntech
An over size bullet is swagged to the correct size within it's length of travel in the barrel. Nothing to worry about.

Not if it's to small, which can cause offset when entering the leade

How is an over size bullet too small?

As long as I have been shooting jacketed bullets (over 60 years) I have not encountered a problem with the fit of jacketed bullets in rifle barrels providing one uses the correct caliber for the barrel... rifled barrels and jacketed bullets are very precisely made.

 

[bearhunter]

Quote Originally Posted by guntech
An over size bullet is swagged to the correct size within it's length of travel in the barrel. Nothing to worry about.






How is an over size bullet too small?

As long as I have been shooting jacketed bullets (over 60 years) I have not encountered a problem with the fit of jacketed bullets in rifle barrels providing one uses the correct caliber for the barrel... rifled barrels and jacketed bullets are very precisely made.

I didn't realize were were specifically discussing "oversize" bullets. I agree completely with that.

I can give you a very good example, you should be familiar with.

303 British bores can be found with bores measureing anywhere from .309 to .318. There was a time when components were available in .001 increments, from .308 to .325, made by companies like CIL.

Some war time production rifles had very tight bores. Two of the Pakistani No4, MkII rifles I owned had .310 bores. Maybe because they standardized to the Soviet 7.62 diameter of .310???

Both of those Pakistani No4 rifles would shoot .308 diameter bullets quite well, but would overheat quickly with .311/.312 bullets and didn't shoot nearly as well.

The reason those bullet diameters were manufactured in relatively large quantities was because of varying bore diameters with similar chambers.

I still have a 50 count box of Green/Red/White CIL bullets measuring .315 diameter for the 42 date Lithgow No1 I used to have with a .315 bore, chambered for the 303Brit. It wouldn't shoot smaller bullets well.