I'm also looking at alternatives to the ELR for deer hunting in my Paramount so I thought this subject to be interesting. I think by the lack of response to your question, most don't think its a good idea to size a FTX down that much. I would think it might damage the copper jacket and result in bullet separation when it hits anything (like deer bone), and could also cause concentricity problems that would degrade accuracy. I could be totally wrong, and If you do downsize them, I would be very interested in seeing your test results, both on paper and on multiple deer.
As an alternative, because I don't want to eat any more lead fragments, I'm looking at the monolithic copper, either the Hornady Monoflex, made entirely of gilding metal at .452 (obviously without it's sabot), or the Barnes Spitfire TEZ, 290 grain, .451, knurled up. My bore is definitely not like your bore. Mine is closer to .4520 than .4525 or .453 near the muzzle, then there's a tight spot for a few inches, then the sized Fury 265STB's slide to the breech plug with little or no resistance. I might get good fit with the Monoflex right out of the package. I haven't bought or tested them yet. With Blackhorn so unavailable, I'm reluctant to do too much shooting.
I called Hodgdon yesterday to see of they could tell me when they're getting another shipment of Blackhorn and their phones were so busy I couldn't do anything but leave a voicemail message. I expect a callback today. Two weeks ago I called General Dynamics, the Canadian company that manufactures Blackhorn, to discuss availability. I spoke to a guy that didn't know too much, but he did give me the name and email address of the Program Manager for Commercial Sales. He should be the guy that Hodgdon deals directly with. My email to him is unanswered.
