Muzzleloading's Point of Impact Myth
Often, you'll hear folks fret and stammer about a "point of impact shift" in muzzleloading, attributed to everything from recoil pads to a change in the rotation of the earth. Velocity does affect point of impact, but with most muzzleloading big game animals still taken in relatively intimate conditions (50 yards or so), the point of impact due to muzzle velocity changes is not as dramatic as you might think. If we miss our deer, we are better off finding something else to blame it on. Here's why.
For an example, I'll suggest a Barnes 245 grain Spitfire at 2000 fps sighted in for a 5 inch kill zone across that load's Maximum Point Blank Range. Using both a standard atmosphere and the published static Barnes ballistic coefficient of .203, that places our bullet 2.40 inches high at 100 yards.
So, let's slow that bullet way down, far lower than we would tolerate by a shot-to-shot velocity deviation: by 200 fps, to 1800 fps muzzle velocity. Changing nothing else at all, not a single parameter except for muzzle velocity, our bullet now hits 3.15 inches high at 100 yards. No deer can live on the difference.
Now let's speed that bullet up, to 2200 fps at the muzzle, changing nothing else. Our bullet now hits 1.94 inches high at 100 yards, using that 2200 fps muzzle velocity. We have a severe muzzle velocity spread of 400 fps, something few of us would knowingly tolerate. Yet, the total effect on trajectory at 100 yards is only 1.21 inches.
Out to 150 yards, there is nothing there to be frantic about. Our 1800 fps MV load hits -0.11 inch at 150 yards. Our 2000 fps MV load hits -0.08 inch at 150 yards. And, our speedy 2200 fps load impacts at -0.07 inches. The maximum change in point of impact at 150 yards is a stunningly small FORTY THOUSANDTHS OF ONE INCH!
Maybe Maxwell Smart could miss it by "that much," but I've never heard of anyone who has claimed to miss a clean kill on a big game animal by .040 in. Have you? At 150 yards or less, point of impact changes due to a slight muzzle velocity variation are simply nothing to fester about. I don't think that even "Uncle Fester" could manage.
Copyright 2006 by Randy Wakeman. All rights reserved.