Well Rigby......you and boatanchor really don't get it. This isn't difficult stuff to understand. Fireform loads are slower if you load them like a std. cartridge. But you don't, why would you? The case blows out quite a bit to fill an AI chamber. So you start at topend for the std case and go up to find best accuracy. In this cartridge my powder is RL15.......if you want to go by what a manual says, top end 50gr load for the std. 22-250 is at 36.0-36.5gr. The best ever 22-250 load for me is with 37.5gr and a 503925, 24" factory barrel/chamber. In an AI with 25" custom barrel/tight chamber, fireform load is 38.5gr of RL15 and a 50 going a bit over 4100. With formed brass add another 1 gr powder (depending on what the gun likes) and get about another 100fps.

The 257 case blows out a lot to become an AI. I don't know what you're doing with yours, but fireform load in mine is with considerably more powder than what a manual says is top end for the std. 257. Velocity is considerably higher also, but this a heavy 28" barrel with tight neck chamber and definitely not a hunting rig. Point being that an AI fireform load uses more powder and is significantly faster than the standard cartridge.

My other AI's, same thing. Fireform loads are well above what's top end for the standard cartridge.