Math for Computing Freebore Order

[artbosco]

I'm looking for a number I can pass on to a gunsmith when chambering a new barrel.

I know the case neck length,.203"), and bullet length from base to ogive,.4270").

The dimension from the case head to ogive just touching the the lands is 1.904". I seat the bullet .010" longer at 1.914".

When I do that I get a nice square mark on the bullet just ahead of the case neck. However, the bullet is being pushed back into the case below the neck/shoulder junction.

Can someone tell me how I compute how much freebore to order to prevent the bullet from being pushed below the neck/shoulder junction ???

Your assistance would be appreciated.

 

[alf]

Why can't you seat your bullet of choice to the length you want
and give, and or, send it to him?
I don't see how your, and his measurments, can/could mirror each other.

Al.

 

[billmo]

Absolutely the best direction to take. One measurement by one person by one pc. of measuring equipment. Takes out all the guesswork if the gunsmith does his part. Bill