First thing first, you need to get a measurement on that barrel. Get a lead bullet and "slug the barrel" then measure it with a good set of calipers. Get a bullet/sabot combo that will suck the slack up.
For instance if the barrel is .502" you wouldn't want to use a .451 bullet and looser fitting Hornady sabots. I would use a larger .452 bullet like the SST 250ML then use a good sabot for the charge like a crush rib. If I'm using a Magnum charge I would use a magnum rated sabot like the Black Crush Rib or maybe a MMP HPH/24. Or let's say a Powerbelt, the 270 Platnum or 250 Aerolite in a .- 500" barrel under a mag load.
250 Hornady in quick sabots should be decent if not pushing them hard, like with with the 100gr load posted. However if the barrel is on the large side range (I've seen and heard of many like .498" - .506") then it won't matter because its probably too sloppy.
Also check you local hinting regs, you might not be able to use sabots. In this case you would start the adventure with full bore conical.
Good luck!
