David V
Not to throw cold water into the mix, and I know there are those who would argue this point, but the selection of barrel twist is important if you are looking for that extra 75 - 100 fps,i.e. you needed to go with the slowest twist that will adequately stabilize the bullet, a 1:9" twist in this case). I also had an extended discussion with Tim North at Broughton Barrels on this, and he agreed that a 1:9" was the way to go, and indicated to me that the 1:9's were doing the best. I know the Sierra box says a 1:8.5" twist or faster, but a 1:9" twist is fine for the 175 Sierras, the Berger 180 VLD's, Cauterrucio 176 VLD's, etc. In my opinion, a 1:8" twist will run your pressures up higher faster than a 1:9" twist would have, but since you already have the barrel set up, you have to work with what you have. I just did an article on a 284 Win long range rifle I made up with Alan and Dan Warner that was published in this March 2006 issue of Precision Shooting, if you want a copy e-mail me and I will send you a copy, and a copy of my reamer print as well. My e-mail addresss is rcw3@erols.com It was set up with a reamer I made up to shoot the 175 Sierras at 1000 yards. Both H4350 and H4831SC worked very well with the project rifle last year. Some options to lessen pressure and to try to get your velocity up,1) try a slower burning powder, but I don't know that that will get you where you need to go with that cartridge because any slower than H4831SC is approaching the point of diminishing returns;,2) if you have a chamber that was cut with a factory type reamer with a short throat, have it throated out to the point that when the bullet engages the rifling, the junction of the boat tail and bearing surface of the bullet is about .015" ahead of the neck and shoulder junction of the case. This would put your OAL around 3.140";,3) Generally, stay away from magnum type primers, they tended to run pressures up prematurely in my testing and did little or nothing for accuracy or velocity in my rifle;,4) Use moly bullets to try to ease the bullet's engraving into the lands and through the throat and to lessen the pressure spike,I don't typically use moly, but it can help in some cases). I don't know if any of this helps, but let me know if I can otherwise help.
Robert Whitley