Pottsy,

I would bet you could go higher pressure & velocity if you got your hands on an 1886 Winchester, especially if a modern one. One gunsmith years ago actually chambered an 1886 in .300 Winchester Magnum and used it as a single shot to see how much pressure the action could handle. The action did fine with no wear with any load that could be crammed into the .300 Win. Mag. case. The action the smith used was an old 1886, I think 1920's or 1930's vintage.

Richard.