My brother just picked up a mould for a 600gr.FN from Buffalo Arms in the States. It's for his custom Target sighted 11 pound 4 ounce M74 Sharps. It doens't take long to add up to $1,000 for sights. The Sharps is also chambered for the .50 Alaskan. That's quite a ctg. when loaded with modern powders in an action that can handle some pressure. We've been shooting .50 Alaskan's for about 15 years, but mostly with black powder and lead bullets. Both had McGowan barrels, 24" twist - mine was consistant 1-1/2MOA at 100yards and 3/4MOA at 200. Same 1 1/2" groups at both ranges.

I'd expect that 18" twist in a .50 will handle about any weight you'd care to shoot.

Interesting concept rifle.