Freebore - Same Bullet BUT... Different Cartridge

[Jarhead6870]

Logic tells me one thing but if there's one thing I've learned over my years of shooting, logic doesn't always give you the right answer. So, the question...

I have a barrel chambered in a straight .284 with a .218 freebore shooting the Berger 180 Hybrids with 0.020 jump; this places the boat-tail/bearing surface just forward of the neck/shoulder junction. Now, if I want to shoot a 7 SAUM using 180 Hybrids and seat the bullet to the same boat-tail/bearing surface and neck/shoulder junction and have the same jump, would I use a 7 SAUM reamer with the same .218 freebore?

Again, logic tells me it would be the same but I would like confirmation before moving on...Thanks

 

[fkimble@charter.net]

You would need to measure the neck length of the two cases and adjust freebore to match the difference between the two cases. IE- if 7 saum neck is shorter by say .100, then more freebore, .100 would be required to keep the bases of bullet equal to shoulder neck junction. Lay out the two cases with bullet next to them for a visual.

Frank

 

[Hohn]

You would need to measure the neck length of the two cases and adjust freebore to match the difference between the two cases. IE- if 7 saum neck is shorter by say .100, then more freebore, .100 would be required to keep the bases of bullet equal to shoulder neck junction. Lay out the two cases with bullet next to them for a visual.

Frank

Exactly this. Great post.

 

[Edd]

The SAAMI specs show a 7 SAUM case neck to be .026" longer than a 284 Winchester case neck.