Just musing over 22LR and impact change vs velocity.
At around 1,000 fps even a 10% velocity difference (say 900 fps) only changes time-of-flight to 100 yards by a small amount.
If the average velocity for the first 100 yards is 1,000 ft/s, it gets to 300 ft in 0.300 sec. At 900 ft/s it would take 0.333 sec to get there.
I used THIS WEB CALCULATOR to compute the distance fallen per time - https://www.omnicalculator.com/physics/free-fall
In that extra 0.033 sec, the bullet only falls another 0.21 inches - about one bullet diameter.
Yet purists would fret if the velocity spread were far less than 100 ft/s with a 1,000 fps average…!
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On the other hand, if the muzzle of an 18” barrel moves just 0.01” due to vibration or bad technique, that translates geometrically to 3,600 inches/18 inches, or 200 times 0.01", or a full 2 inches, at 100 yards.
So when we miss, it really is mostly US, not the load, or the gun.
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But what about a centerfire high-velocity cartridge, like 223 Rem or whatever...?
With a cartridge averaging 3,000 ft/s for the first 100 yards or so, a 10% spread in velocity would drop all the way down to 2,700 ft/s, with a 100 yard (300 ft) flight-time of around 0.1 sec or 0.111 sec respectively. That extra 0.011 sec would only cause bullet drop of 0.6 mm or 0.02”…! Not even noticeable without using calipers on the target to measure your groups. But of course we generally might want to shoot well past 100 yards with something like a 223 Remington or whatever longer-range cartridge we are using...
With a cartridge in the 3,000 fps range, at 300 yards you’d have a flight time of 0.300 sec, and a ten per cent decrease in velocity the flight time would increase to 0.333 sec, the extra 0.033 seconds resulting in the same drop at 300 yards we saw with the 22LR at 100 yards:
Still it is only about 0.21 inches - one bullet diameter - at 300 yards...!!!. [/i]
So unless my math is way off, maybe we shouldn’t worry too much about velocity variation (not that I really ever did much).
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Another fun concept involving the 'math' of shooting, is that since a bullet exiting the muzzle of a 24 inch barrel at 3,000 fps more or less averaged 1,500 fps travelling those two feet, that means it was only in the barrel 2/1,500ths of a second, or 0.00133 seconds. Many match shooters will say even lower numbers, but certainly a barrel can 'wear out' after 3,000 rounds, certainly by 6,000 rounds, for some of the really high-pressure, high-velocity chamberings. Say 7,500 rounds just to make the math easy - 7,500 times 2/1,500 = 15,000/1,500 = ten seconds.
Thus one can say that it only takes about TEN SECONDS of actual use to wear out a barrel...!
