While it isn't Montana, I will share with you the load and a hunting story from one of my pop's hunts years ago.
He was invited on a cull hunt for mule deer on a ranch out around Big Bend. I don't know the detail surrounding it all but I know how it all went down. He had always shot an O3A3 which he sporterized back in the early 60's, and as such he mostly shot surplus ammo through it as well. For target loads he simply shot the 147gr ball ammo, and come deer season he simply pulled the FMJ, neck sized the cases and seated a 150gr Sierra spitzer flat base.
During the hunt there were a total of 7 hunters, and a guide who spoke very limited English. Pop said every time the fellow would spot a deer it would take them 5 minutes to calm him down enough to understand where he was wanting them to look and then another 10 or so to find the mule deer he was pointing at, up on the canyon ridges.
There was one thing about my pop, you never bet against him when it came to shooting. He took many a dollar putting a BB through the eye of pigeons roosting in the decks of the place he worked. Anyway the fellows would shoot in rotation. He said they all had this that or another type of magnum and none of them seemed to be able to hit the sides of the canyon much less the deer. IT always came down to him and his ol '06. He might shoot 3 or 5 times but in the end he killed every deer they had tags to get on that hunt. He said he had never shot so far or so many shells to kill so few deer in his life.
This was before laser range finders and back in the early to mid 70's. The fact remains though mule deer haven't gotten any tougher, and the bullets have only gotten better. I can also say that if your within 300 yards of any mule deer and hit it honestly with either a 150 or 165gr load through the boiler room you'll have your deer.
If I were you and your already shooting good groups with the load your using I would use it and be happy.
I wish you the very best of luck and hope you find your trophy.
Take care,