I just got through with my second load development test today with my 6br improved and I thought it was interesting how awesome this cartridge is. I fired a total of 21 different loads involving 2 powders and 3 different primers behind a 105 AMAX and out of 21 loads, 20 had a standard deviation in the <font color="blue"> SINGLE DIGITS!! </font>
My largest group at 100 yards in thick mirage was .8" and I had several loads that were in the .2's with one going into the .1's!
At 1000 yards in swirling wind, it had no problems hitting my 15" gong if I doped the wind right. Later on in the evening, it shot a nice 7.5 inch 6 shot group of which I was well pleased.
I started at 30.0 grains of Varget and ran up to 32.5. 31.5 grains of Varget and a Fed205gm primer yielded an avg velocity of 2928 and an sd of 1! 32.5 grains gave 3013 fps with an sd of 6. I also tried RL15 and it shot extremely well, and was just slightly slower than Varget giving about 35 fps slower velocity with same charge.
I bought into the suggestion on 6mmbr.com to run a cci 405 magnum primer to get an extra 100 fps more than the Fed or Win primers and I can honestly say that was a load of horse pucky. With the same charge, the cci primer was only 4 fps faster in my gun than the Fed or WIn primer. They did shoot well however, but then again, so does anything else that I want to stuff into that chamber!
I am running about .0015 thousands clearance on this brass and use a .262 bushing for sizing.
My barrel is 26.5" long Krieger 4 groove, 8 twist. This combo gives what I believe to be the <font color="red"> ULTIMATE 1000 yard practice </font> cartridge going. Yeah sure, my 22-250 improved fast twist drops less at 1k, and my six-five two eighty-four beats just about anything I've run it against on a windy day, but it is just a pure joy to burn only 31.5 grains of powder and hear it ping the gong at 1k every shot.
If you are considering getting into the 1k game, and a budget keeps you from buying powder and barrels by the truckload, you should really treat yourself to the 6 br improved fast twist. [img]/ubbthreads/images/graemlins/wink.gif[/img]
Here is a pic of the little boom stick: