you mention just using 240 jacketed data when working up 250g hardcast loads and advised not to exceed of course
I would think the FPS would be almost identical, the 250g should be a tad slower based on weight alone, but HC tends to shoot a tad faster than jacketed according to everything I have read/heard.
As Greybeard advised, do not exceed the load listed for the 240 grain jacketed data. In fact, you should pick a charge about mid-way down or lower and work the load up and look for signs of overpressure.
A 250 grain bullet being heavier may cause or create a little bit of extra pressure (obviously) and believe it or not, sometimes the amount of extra pressure generated may actually cause that bullet to move at a higher velocity than the lighter bullet. Also, keep in mind that when using cast bullets, you typically generate much more pressure than is generated with a jacketed bullet due to the fact that the cast bullet fills in all of the grooves and basically seals the barrel more efficiently, hence, building even MORE pressure. So basically, you're adding two factors to the load which increase pressure; using a cast bullet and a heavier bullet. The only control you have left to keep the pressure in check is to lighten the load.
Geez....I hope that made sense.
Sometimes it's hard to express these kinds of things in writing without going on and on.
