Please help me understand the ballistic advantages of increasing the freebore. I understand that longer bullets can be possibly be used while maintaining powder volume but pressure limits remain the same and pressure drives bullets. I have read that some shooters increase powder amount using a slower burning powder and thus increase MV and ME.

Any comments appreciated. If this is a dumb question, please excuse.

Not dumb.
I have a drawer full of throating reamers, because some guys want to use a heavier and longer bullet. Or they are using Barnes bullets that need a longer jump of about .050.
Or for a Weatherby, the made a really long free bore to decrease pressure.
Or like a 257 Ruger I have, they made a super long throat for absolutely no reason, so I seat the bullets .1 into the case and use 25-06 load data. By seating the bullet out, you effectively create a different larger case capacity cartridge.
Some guys throat out 45-70s to get more powder space; original 45-70s have no throat at all.
458 Win has like a 2 inch tapered throat.
6.5x55s have a very long throat for the long military bullets and they sometimes don't like light hunting bullets.
Lots of reasons, good and bad; but there needs to be a plan/reason. And in concert with your mag length.

Most 6,5*55 shoot well with 85gr 100gr varmint bullets even then they are throated for 160gr bullets. My 300 blackout shoots well with 110gr bullets and its throated for 220gr bullets a half inch jump seems to be ok for it if the shape of the bullet fits it.

I always increase the throat length for a favorite bullet, to just fit the mag length.
You will usually gain a little capacity/velocity that way.
I think the .458 was given the long tapered throat to reduce pressure quicker, and reach the velocity advertised.

What dpcd sez...

Its a good practice IMO, Ive used it in many calibers but mostly in the 8x57 and 7x57 and in some cases thats what those caliber came from the factory with from Mauser..My 7x57s shot an inch with 175 grs. in long throated as did the wonderful deer bullet, the 130 gr. Speer..all of them..

Its touted by some that it ruins accruacy as the light bullets have to make that jump..THAT HAS NEVER BEEN THE CASE IWTH MY FREEBORED GUNS, and thats been many 8mm and 7mm Mausers, and other guns Ive modified...I believe those claims are misguided and based on poor investigation and too much guess and by gosh..

I have run tests, from seating the bullets touching the rifling, to them being seated so deep a slight tough would drop them into the case.

Hardly any difference in accuracy.

quote:

Originally posted by Saeed:
I have run tests, from seating the bullets touching the rifling, to them being seated so deep a slight tough would drop them into the case.

Hardly any difference in accuracy.

Thanks Saeed. That helps me put my mind right.

I've always felt a little guilty about not chasing down some magic number of thousandths off the rifling for each bullet/powder/rifle combo when others seem to have found that step to be an important contributor to accuracy.

I never noticed any difference in group size that I couldn't attribute more to my lack of skill than to a few thousandths off the rifling.

I'll proceed with my old habits, but with a clear conscience.

As you increase freebore you are increasing the distance the bullet travels before hitting the rifling. So all things else being equal the maximum pressure will be less. If you start adding powder to get back to that same pressure you will see increased velocity.

I've always thought that the faster a bullet is traveling when it hits the rifling the more distortion the bullet will incur, which seems like a bad thing. But I don't have any evidence of that and Saeed's results seem to prove otherwise.

In most cases, its probably a good idea that the chambers match the magazines..A good long throated chamber with a matching magazine is very desirable, holds more powder, less pressure and more velocity, so whats not to like?

Problems arise when the magazine and chamber don't match..and many rifles do not match up, in fact, many if not most factory rifle dont match the throat or so it seems to me...