Re: wide extreme spread
ES won't raise up and bite you till you get to 600 yards, maybe 500.
I just pulled out my copy of Sierra Infinity 5 and plugged in 175 grain Matchking at 2550 fps and then added 35 fps and subtracted 35 fps to give your 70 FPS ES and here is what I got:
Velocity Bullet Drop Inches
2515 489.54
2550 474.36
2585 460.18
So assuming you are zeroed with 2250 fps you slowest round is going to hitover 15 inches lower and your fastest round is going to hit over 14" higher. Thusly you have an extreme spread of 28.74" of elevation alone before you add in other things like heart rate, wind, mirage etc.
The 1000 yard Highpower Target has a 20" 10 ring thusly you have ammo that wouldn't print 10 ring shot from a machine rest in zero wind conditions.
Now lets look at 20 feet per second extreme spread:
Velocity Drop in Inches
2540 478.78+
2550 474.56"
2560 470.39"
Thusly you are now looking at 8.48" vertical dispersion and the X ring is 10 inches so you have ammo capable of shooting X ring.
I saw the record 1000 yard target shot a Perry a number of years ago. 200-17X and if memory serves me correctly he had one 12 o'clock shot at the 10 line and two 6:00 O'clock shots at the 10 line so he had about a 19" vertical dispersion. If he had been a click off up or down he would have lost a shot to elevation alone.
One of the two years I came second in the Canadian Cup I was I think down six points. I lost four of those six points due to a round that gave me a 6 ring hit at 6:00. Two more points and I would have won the Long Range Championship but that is how it goes in long range.
The problem with figuring the extreme spread is the long run average. 10 rounds won't do it.
If you want to see what your ammo and rifle is capable of chronograph two sighters, record them and then shoot thirty continious rounds at say 40 second intervals and run the numbers every 10 shots. I think you will find that the longer you shoot the ES will start to creep upwards.
This is also a good indicator of whether your barrel is properly stress relieved as when they heat up they tend to change the alignment and group will start to walk.
Even better put up a target at 600 yards and have someone plot your shots while you are shooting.
The Marine Corps Teams used to train with no spotters. You got two sighters and then they left the target in the air for 20 shots and you worked off the mirage and wind flags and you didn't see your target till you got to the pits.
Bottom line is up close ES is not that critical but at long range it will rain all over your parade.
