The reason you are probably not getting a lot of responses is that people might not be familiar with that rifle. I am not myself, and it is a major consideration when you handload that calibre.
I own a stainless Marlin Guide Gun in 45-70 with a muzzle break. I can find upper end loads that come mighty close to the lower end of a .458, a calibre most used in Africa.
A load of that type is not suitable for a trapdoor. In fact, my guess is that it is NOT a load for the Winchester.
If in doubt, I would suggest contacting the customer service department of that company. I'm sure you'll initially get the typical "we recommend clean factory loads of good quality," but if you convince them you are not a nut or a hot-rodder, I'm sure someone there with grease under his nails can get you some reality based info. Good luck.