Howdy, Been a member for sometime though I rarely post. Do a lot of reading though. I have a 264 Win Mag Sendero II. It's got a 1/9 twist, standard Remmy trigger though it's all been worked over by Clarence Hammonds. I'm trying to develop a load for it using 140 SMKs. I'd called Sierra and gotten a load range of something like 55.?grs - 62?grs of IMR7828. I can fire a couple of rounds and have them touching and the next three rounds are 3/4 of an inch out. Typically, I start at mid-range - I feel that's a safe thing to do though with 264s you gotta' be careful because they generate pressure spikes with even slight changes to load weight. Anyway, I've got through like...25 rounds and I'm still no where near where I think this gun should be. My question, as the title suggests is, how many rounds should I reasonably expect to have to shoot while developing a load? And by the way, if anybody has a good, safe load using IMR7828 or IMR4831 please let me know. Thanks in advance.