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 sighted in at "5 inch
kill zone 100 yard Maximum Point Blank Range," using both a
standard atmosphere and the published static Barnes ballistic coefficient
of .203. With a muzzle velocity of 2000 fps, that places our bullet
2.40 inches high at 100 yards terminal distance.
So, let's slow
that bullet down, 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 with that 1800 fps muzzle velocity. No deer can live on the
difference.
So, let's speed
that bullet up, way 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 terminal velocity. We have a severe muzzle velocity spread
of 400 fps, something few of us would knowingly tolerate. Yet, the
total effect at 100 yards is less than 1-1/4 inches: about 1.21
inches grand total.
Out to 150
yards, there is just nothing there to be frenetic about. Our 1800
fps MV load hits -.11 inches at 150 yards. Our 2000 fps MV load
hits -.08 inches at 150 yards, and our speedy 2200 fps load impacts
at -.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 even "Uncle Fester" could
manage.
©
March, 2006 by Randy Wakeman
