getfoxy,
The problem is that each rifle and ammo combination reacts differently to being exposed to 50,000psi plus. One rifle might take a real bucket full of powder and like it. Another might just take a pinch and can't take any more.
I'd start at a safe minimum load of 30gr of H380 and work up by .5gr increments to probably no more than about 34.5gr. But remember this. Its very, very tempting to get every inch of pace out of a 22-250. For that reason most guys will push the round to its limits, but if you have a look at the ballistics sheets there's little gain in going for that extra 50fps. That extra 50fps will burn barrels out faster, wear out brass quiucker and give you 2/10ths of nothing extra in field perfromance. What's more important is that it is accurate. To each his own, but I'd go for a moderate psi accurate load. Zipping past them at light speed won't scare them to death. You have to hit 'em.
FWIW