Here's what I learned the first time I fired my 338 RUM at extended distances. I have a Rem 700 with a 27.5 inch barrel and shoot the 300 Sierra at about 2750fps (now). The rifle weighs about 15 pounds and I have a Leupold 3.5x10 VariX-III Long Range (M1 version)
This is from a post I made a while back.
I know you're all chomping at the bit to hear how it went .
I only had time to fire 7 rounds but it was very enlightening.
I used "The Thing" to get the distances and come-up. Only known good data I had for the 300 Sierra as 100 yards and 413 yards.
I used the computer program discussed by Peter Cronhelm in the Ranging Ballistic program.
The target was a 4 x 8 foot piece of plywood. The Point of Aim is a 14" wide and 17" tall white blob of paint.
My first 3 shots were from 1197 yards, GPS determined. I used the 1200 yard data provided by "The Thing". Figured a 5 mph full-value wind from 9 o'clock. First round (cold bore) struck the backer 12" right and 5" high of point of aim. Second and third round struck 30" high and essentially no right or left deviation. I made no data changes as this is merely a test run for basic data.
I moved to 1730 yards, I couldn't get a good view of the target at 1760. The Thing predicted 66.1 MOA come-up and 4.4 MOA wind. I knew the last two rounds at 1197 were high so I elected to use 64 MOA.
The fella in the impact area, brave sort of guy, was 50 yards left and 100 yards from the face of the target. First round was a no impact observable, as were the remaining 3 shots. We had a couple of cease-fire situations and he couldn't find the impacts. The impact area was grass, about 8 inches tall grass. The light was failing and I drove back to the target. After many minutes of combing grass we found where 3 of the 1730 rounds had struck. They were about 7 feet high, above target center and one was about 2 feet right from target center.
After reflecting on the situation I dicovered two errors in thinking. First is the that I used the data provided by The Thing, which I should have known uses the come-up data for the next increment of range. I had selected 50 yard increments and the comeup data I used was for 1750 yards, not 1730...my error. I believe that at that range every 5 yards is 10" of drop at the target, this would have been a 40" high error, over 2 MOA too much data. I also only subtracted the standard 2 MOA of data error that I had experienced at 1197 yards and I probably should have extrapolated for the added distance? Also, and I believe Darryl and others may have mentioned this, the BC for the 300 Sierra of functionally higher than .768 as I had used.
I had a good time, didn't get many round off but I'm ready to go back this week and shoot again. I also need to get actual data for all my standard distances to 1000 yards.
The guy in the impact area was MOST IMPRESSED with the impact of the big 300 grain Sierra. He's observed many 308 impacts and clearly stated he wanted no part of being the recipient of one of those bullets. The noise of the supersonic 'crack' was audible to many folks, not only the folks directly under the flight path. The rounds were still superconic at the 1730 yards distance and should remain so until about 2000 yards, this is with an initial muzzle velocity of only 2707 fps. "
In addition to the items mentioned above I also concluded that I need elevation settings at my FFP and the TRP. I believe even a small angle will make a considerable difference at 1700 yards. I haven't been able to go shoot at these distances yet but it's nearly Spring (yeah, right!) and I'll be trying it again.