The importance of consistent ammunition for Long Range shooting cannot be over-emphasized.
Take for example a rifle that is zeroed at 50 yards, with the only parameter that is varied being the muzzle velocity.
With a muzzle velocity difference of 50fps at 100 yards, the vertical spread is only 0.05 inches. This would make a single ragged hole, thus leading the ladder tester/shooter to believe they have found a great load for their rifle, right?
Compare this with what that 50fps muzzle variance results in at 1,000 yards: a vertical spread of 1.37 MOA, or 14.3 inches! A good chronograph is an essential part of your toolkit when testing loads, and a good load for your rifle not only has to yield a tight group at 100 yards but needs a standard deviation (SD) / extreme spread (ES) as low as you can possibly get in order to enable good long range performance.
Note: this is a simple result of a theoretical calculation. The fact is, with an extreme spread (ES) of 50fps, the theoretical 0.05” at 100 yards may be fictional, because of the rifle system’s harmonics; this may not be observable in nature.
Image credit: Tony Darst
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Low standard deviation (SD) / extreme spread (ES) becomes much more critical for precision impacts at distance than at closer ranges.
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