If you're trying to stop a large aggressive bear with a handgun(any handgun),don't even think about body hits.A solid brain hit will be the only thing that matters.That being the case,it stands to reason that the bullet should be non-expanding to penetrate the skull.Don't listen to anyone who tells you otherwise.

Shotgun slugs have killed bears but are generally poor performers on large bears and that includes the brenneke slug.

Your rifle is the best thing and your guide will be doing whatever camp chores are needed and so there will be no need in not keeping your rifle handy.

STOPPER rifles will be in the class of weapons which are more common in Africa "which does NOT include the 45/70".Even with good shot placement,the 375 Holland & Holland is considered minimum among "stoppers".

I've killed bears with a 30/06 and with good bullet placement,it will do the job.Needless to say,your 300 WBY is fine assuming you shoot it well.

Bear guides as well as other guides in Alaska are used to seeing "dudes and greenhorns"from the lower 48 show up with all manner of pistols and such in preperation for a bear charge.If you carry a pistol,they will roll their eyes (when you're not looking).

There is always someone who knows someone who knows someone,etc in Alaska who recommends this and that.Such information is usually just as useless because the majority of people living in Alaska live in communities and don't know anymore about the bush than the average New Yorker.

I lived in an isolated cabin about 25 miles from the nearest human being and had a lot of exposure to bears.