I have a Weatherby Accumark in 300 Win Mag and would like to know if it is possible to open the bolt face to accept the 30-378 cartridge, have the barrel rechambered and make it feed properly?
It is the large Mark V action and they make the Accumark in 30-378 so I think it might be possible.
If anyone has done this before or has any input I would appreciate the info or advice you have to offer.
Thanks,
Wayne

A friend opened up a Mark V Wby to accept the .416 Rigby case (same size as the .378 Wby) and uses it as a .338-416 Rigby Imp. longrange hunting rifle. The loaded round is way too long, 300 MKs, to consider anything other than a single shot. The .378 extractors are available from Jack First and other parts suppliers.

Also, by swapping Wby parts in, you can make it a two shot repeater, anyway. - Dan

You should have no problems,I know of a 300 that was turned into a 416WBy.
Open up bolt face ,get suitable extractor,and you may need the 378 type magazine box and you will need the follower if you want a repeater.
A specialist Weatherby dealer like www.skeetersweatherby.com
should be able to arrange the parts.
A thought,
Maybe trading your 300 for a 30-378 maybe a cheaper and better option.
Good luck,
Regards,
Charlie.

Thanks guys for the info and advice. I think I'm going to look into the possibility of a 30-338 Lapua Mag instead of the 30-378. The 30-378 is a longer case and when loaded with the 240 SMK it would be too long for the mag box, thanks Jay for the heads up on the length issue.