@Ontario Hunter
Yes there are a few suggestions I can make, firstly lets deal with assumptions. By your “and still beat me up” sentence, I am assuming you want to find the crossroads of buffalo killing and reasonable recoil. Buffalo killing means accuracy + that 300gr pill moving at about 2150-2300fps.
And reasonable recoil is just lower recoil.
So, a 307gr pill moving at a particular velocity will always contribute the same to the total recoil of the system, BUT the amount of powder used to propel said bullet will also contribute a lot, and grain per grain the powder adds more to recoil that the bullet mass. So, what this means is you want a very bulky powder, that is fast burning to quickly spike the pressure to get the velocity you need, while also filling the case with a minimum amount of powder. For that I would try two powders. Varget and IMR 3031. With both I start around 70gr, and then move up or down depending on what you are getting. Both are easy to find in Canada, and I would start with 3031, and then move to varget.
You are going to run into the volume issue, so you may need to stuff some wadding in there. The other thing I have found with respect to accuracy, especially with monometal bullets. Is the importance of seating depth. So do play around with this. Once you find a load that gets you the velocity you like, then start varying the seating depths. Like 5 rounds with the bullet just touching the lands. 5 rounds 10 thou back from lands, 5 rounds 20 thou back… And so on. You will find a node where they shoot more accurately. With mono metal bullets I tend to start at 40 thou from the lands, and then make loads +- 10thou =- 20 thou and so on.
Now if I can make two specific recommendations you maybe don’t like, here they are:
1. Try a different bullet.
https://store.prophetriver.com/north-fork-423-cal-340-gr-soft-point-50ct/ North Forks have been accurate in every gun I have tried them in. Here is a lighter weight one. Again 70gr of varget should be a good place to start.
2. Move to a different gun/cal. If you are backing down to a 300gr bullet and looking for lighter recoil. Something like a 9.3x62 might be ideal. It only takes about 52ish gr of varget to move a 300gr swift a frame at 2250~ish fps. This would be soft recoiling and deadly on buff… As a bonus you could load up some 250gr northforks or nosler accubonds and have it be a dual purpose gun for plains game. I shoot a 9.3x74r drilling with 250 northforks as my plains game gun, and is it sweet shooting and deadly.