Re: 6mm loads
Hi There! I shot out many bbls on the exact same rifle that you are shooting. I lived out West at the time and shot p. dogs and Rock chucks with my 6mm's. I too rarely shot past 500 with most of the long range shots being in the 350 yard range.
I shot the 60g Sierra on coyotes and my 60g hp on p. dogs and crows after trying a flock of different bullets of heavier weight. I later on found the Sierra 80g Single shot pistol bullet with a very heavy load of IMR 4064 to be very fast and accurate and blew up very well on everything. Sierra now makes a 80g Single shot blitz Boat tail that is a very accurate bullet and highly explosive, but gives great holes in coyotes also.
I found that the bullets in the 70g range to give the highest velocity with less copper fouling, and the 85g bullet and up really coppered my bbls up fast while making cleaning a real chore. If you wanted to go to a heavier bullet, then my first choice would be the Sierra 80g Blitz BT.
I encourage you to spend some time on a ballistic's program to educate yourself on bullet drop and wind drift...it is a real eye opener to say the least. Do not be deceived, 200 fps makes up for a lot of B.C. on a bullet, and time of flight has a lot to do with wind drift.
Also, for varmint hunting where rapid shooting is taking place, copper fouling is a killer of accuracy. The slower bullets with the longer bearing surface will copper up a bbl quicker than a faster light bullet with less bearing surface. You will have to experiment, because there is a balance between copper fouling and accuracy taking into consideration the number of rounds that you will like to fire in a string.
As a general rule of thumb, I found the custom bullets made on a J-4 jacket and Sierra bullets copper foul less than Hornady or Nosler bullets.
The Hornady 87g with poly tip is reported to be a great bullet, but the copper fouling with these long bearing surface bullets will be a bear, no doubt.
By the way, when you start running the numbers that you are shooting on the 55's, it will amaze you how well the 55's at 4000+ do on wind drift and bullet drop out to 500!
What kind of shooting are you doing?