Some Thoughts On Sighting Your Round Ball Rifle
OR
The Three Inch Rule
One of the questions that many muzzle loader hunters often ask is;
"where should I sight my round ball to maintain a reasonable point blank
range (PBR) for big game hunting out to 100 yards"? Usually other
variables are included with the question such as; caliber, charge, powder,
lube, etc., etc.?
The answer regardless of variables is simple; Sight to hit dead on at
100 yards and your maximum midrange trajectory will be right around three inches
. That answer will pretty much remain unchanged for the majority of
rifles and in calibers from .36 caliber up to .75 caliber. They pretty
much shoot with the same trajectory given the typical velocities these calibers
are shot at. Another option would be to sight for a point of impact (POI)
1.5 inches below point of aim (POA) at 100 yards and, theoretically, your rifle
will never shoot outside a three inch circle at any point between the muzzle and
100 yards. You and your rifle together will shoot outside that circle, but
how far out is for each shooter to determine by shooting under various
conditions.
I don't advocate the use of a .36 cal or even .40 cal for big game hunting,
but I included those two just to illustrate the universal application of the
three inch rule.
The chart illustrating the three inch rule was generated using William
Frenchu's Ballistic program version 4.13 and applying the British Round Ball
Table of 1929. The ballistic coefficient (BC) for each ball was derived
using Frenchu's formula specifically tailored to the British Round Ball
Table.
The front sight height setting was .70 inch above the centerline of
bore. Sight height varies with different rifles, but those variations
don't effect the chart results significantly.
The velocities applied to
each caliber are based on my own experience with .36, .45, .50, .54 and .58
caliber rifles and the experience of other shooters with the remaining calibers.
Click this
link to view or download the chart in pdf format. | 
