You mentioned your .460 Weatherby magnum calibre rifle which was built on a Brevex mechanism . May l ask which firm built your rifle and how many cartridges the magazine could hold ?
Also , do you use traditional metal envelope bullets or modern homogeneous metal bullets ?
The gunmaker was SIPP in Strasbourg/France. The rifle was built in 1974 , but I buy it at the beginning of the nineties. The magazine hold 3 cartridges.
I used different bullets , initially the classic 500gr SP Interbond from Hornady and to time the 500gr PP SN from Woodleigh. I have only used a lead-free bullet one time , the 450gr TSX from barnes. They were very accurate , but IMHO a little bit too soft. But as I said , I have only one buffalo shot with , what is not enough to judge a bullet.