OP. My two sense for your situation is to grab an Accura .45 and put a quality scope on it. The ELR 285 push with a max load will stabilize just fine and I have seen several sub 1 inch guns with this setup. A scope using a reticle out to 300 would be pretty easy and if you want to shoot father I would recommend a scope with a quality turret. This would potentially pigeon hole you into shooting the ELR but there are to many benefits to a smaller diameter bullet for me to go to a 50 cal if its legal for you to do so. Encore is right that you can build a better gun than the 45cal CVAs but my experience has been positive while shooting the ELR. Spend your time and money elsewhere like on an optic. Not sure what your budget is but if its under a grand for a scope the $200 your will spend on a sizing die would be better served on a scope IMO.
If you hunt for a season or two and decide you enjoy it but need to squeeze more performance I would hit Encore up for recommendations for bullets, barrels, and builders.
I have set up several of this setup for buddies and they have been excited to get out to 3-400 yards consistently.
Accura (pick your poisin but I like the new features of the X series but haven't actually got to shoot them yet)
Leupold VX5hd 3-15 wind plex
Warne Mountain tech bases and rings (duramounts suck)
285 ELR
80-84 Weighted grains of BH209
I think that one thing guys miss in the hunting community when muzzleloading at ranges past 300 is how small your margins of error are past 300 yards. Big heavy slow bullets drop very quickly and get blown around by the wind. A range finder with atmospheric sensors are a quick easy soloution, ballisitc apps work, or a kestrel. At 400 yards temperature swings that deviate from your dope chart can make you miss animals pretty easily. The applied ballistics ap ($30) can help if you have cell service to update the enviormentals. The sig 2400 abs, Revic, and leica 2800/3500.com rangefinders all have this feature and can just read out your bullet drop in MOA/Mils.
