Anyone see a correlation on "freebore" calculations?

[350JR]

I am looking at freebore for the wildcat I'm working on and I just don't see any relationship, not even close, or how Weatherby came up with these freebore lengths in these rounds.

Some with the same general case capacities, some with same calibers (and bullet lengths), same velocities.etc etc........and different freebore lengths?

Bullet body length has to come into the equation, but I don't see anything close to any kind of calculation but do see a kind of relationship in a couple comparing NECK length. The 375 and 378 have radically different neck lengths and the freebore seems to relate.

Sorry if this is a repeat. I couldn't find anything in search.




God Bless

 

[Oldtrader3]

You would probably need to go back to 1959 or something to find any basis for Weatherby freebore. It may b an over the thumb length?

 

[Vince]

You would probably need to go back to 1959 or something to find any basis for Weatherby freebore. It may b an over the thumb length?

If there was a "Thumbs Up" icon I would be using it right here. :grin:
"Just a smidge and a tad more. Nope, that's too much. OK, make a new caliber." :grin:

 

[truck driver]

I'm no ballistic engineer but if you think about it what Roy did was figure out the correct throat length to achieve maximum velocity and still stay under maximum safe pressures for each caliber he developed.

 

[350JR]

What is in MY mind on this, for a wildcat anyway, is (1) take the particular bullet you expect to shoot most (or general range of bullets) and measure the amount of the bullet that comes in contact with the rifling in length......and stay under that by whatever margin one feels is mandatory to keep the bullet in the neck by some minimum amount when it contacts the lands and (2) take into consideration the powder charges the round holds and include the velocities it will be expected to run with higher velocities and more capacity equaling more freebore..........that said, its all guess work or "feel" or whatever unless I can find someone that has some kind of mathematical proof of what length of freebore does what.

I know some other manufacturers use a really long throat on certain rounds as well but I've not seen any kind of "list" of such like in the Weatherby mags.

I appreciate the input, gang.

God Bless

My thoughts are that the bullet should still be PARTIALLY inside the neck when it contacts the lands. However the .378 Bee neck isn't THAT much longer than the .375 Bee yet the capacity and speeds are indeed higher.