Re: Free bore
Less likely to get pressure spikes with hot loads.
Seems to give higher velocities with powders that are faster burning than normal for the calibre.
Seems in general to be more likely to put the first shot from a cold clean barrel or a barrel with cold hard fouling into the group.
If the freebore diameter is not real close to bullet diameter then accuracy problems, especially in terms of the limited range of loads that will shoot.
For calibres with big cases and huge freebore such as the 378 and 460 Wby reduced loads down in the 80 grain area become a problem with hangfires. For example the 416 Wby which does not have the big freebore is easier to work with reduced loads than either the 378 or 460.
In my experience and for accurate hunting style rifles chambered in calibres with a big case capacity for the bore size AND provided the freebore diameter is not oversize, then I think overall it is a gain.