I have a .50cal Winchester Apex with a fluted barrel. The scope mounts I have are the 2 piece weaver type mounts and they are rock solid.
I currently shoot a 350gr Hornady FBP with now less than 90gr. of loose 777 and I have bumped up to 120gr of loose 777 with no lose in accuracy. The only time I use 120gr is when I am hunting over open fields where I need the added range. These bullets just are devastating to whatever you hit with them.
So it is safe to say at the most 150 yards or so will be my max range due to the size of the projectile.
I just love those Hornady FBP bullets, I tried them in my sons and some of my friends MLer's and not one of them would not out shoot any bullet that has been tried in them. Out of my MLer the 300gr FBPs where not as accurate but other than the weight everything is the same. I tried all kinds of different loads. They where plenty good enough to kill at 100+ yards just not as accurate as the 350gr.