Shooting Palma Bullets
Sierra 155 Grain MatchKings
1998 was the year for selecting the Palma team members
and there were many articles on the various matches used to select the
Canadian and American teams. My hat is off to the people working for
a place on a Palma Team. Shooting a 1000 yard target can be a lot
of fun if things go well, or may be very frustrating if the conditions or
your equipment is having a bad day.
The "Palma Match" has a fine heritage and tradition.
This also means that it has long standing requirements and regulations.
Which include controlling or issuing the ammunition used at the Palma Match
by all shooters. The bullet, powder, primer, and case I believe has
been selected but the only component that I am sure of is the bullet.
The Sierra 155 grain Matchking or Palma has received the honor of being
the Official 1999 Palma Bullet. This article is about my curiosity
on just how good is this Sierra Palma Bullet at 1000 yards and just how good
does shooter/gun have to be at 1000 yards to hold the X-Ring and Ten-Ring.
The rules have been changed and after the 1999 Palma Matches the teams
may bring their own ammuntion to future matches but it must still use the
Sierra 155 grain MatchKing bullet. So how good is the 155 at 1000
yards?
The first question on how good is the Sierra 155 Palma
bullet may be hypothetically answered with the aid of a ballistic program.
After all, Sierra has the best ballistic information. This Palma Bullet
has most likely been tested by all bullet manufacturers with the equipment
to do so and by many countries for their Palma team. This bullet may
not be one of the most tested bullets in history but most likely has received
all the latest testing on the newest equipment using the best procedures.
So how much muzzle velocity, wind speed, and wind direction variation can
the Sierra MatchKing Palma bullet tolerate and stay in the X-Ring at 1000
yards? In other words how good does the ammuntion have to be in terms
of muzzle velocity standard deviation and just how good does the shooter/coach
have to be at reading the wind changes in terms of speed and direction?
Muzzle velocity variation is a known fact and here
to stay for awhile. But what is more important for the long range
shooter, low standard deviation or low extreme spread of the muzzle velocity?
Both are part of the chronograph's statistical output. Both are very
useful. Standard deviation is the measure of variability equal to
the square root of the arithmetic average of the squares of the deviations
from the mean in a frequency distribution. Thanks for the computer.
So after all that square of the squares stuff, just remember that your
chance for each shot fired is 68.3% for being within plus or minus one standard
deviation from the calculated mean velocity. Your changes are
95.5% for ±2 standard deviation units and 99.7% for ±3 standard
deviation units. The chronograph's extreme spread is telling you
how lucky you were on the five or ten shot string just fired. Fewer
shots per group will increase your luck for a low extreme spread. Use
five shot strings to tell your friends how good your load is and 33 shot string
to tell yourself.
Target 1 shows four 100 shot vertical groups for the 155 Sierra Palma
Bullet at 1000 yards. The mean muzzle velocity was 2950 fps and from
left to right the standard deviation for each group was 6, 11, 17, and 22
fps. This target was generated using one of Silhouette Ballistics
computer programs. The Bench Rest Simulation option in the exterior
ballistic program generates a table for the down range trajectory from randomly
selected velocities. The program randomly selects the velocities anywhere
between plus or minus three standard deviation units for the mean velocity.
Using 100 shot groups you pretty well get the entire spread of the ±
3 standard deviation units. The first one hundred shot group on the
left with the standard deviation equal to six (6) could be representative
of a very good lot of ammunition. The second group on the left had
a standard deviation equal to 11 which may be a better representation of the
"Palma Ammo". The third group with a standard deviation of 17 may be
higher than the palma team wishes but may be the closest. The last group
with a standard deviation equal to 22 is for palma shooter's night mares
and showing the wind affect. Using a random selection process which
selects anywhere between ± 3 standard deviation units will not produce
selected values or population that fits the normal statistical curve.
The odds of selection are even across all three standard deviation units.
Selecting a number within ± 1 units is the same as selecting a number
in the ± 2 to 3 standard deviation group. So the target may
have more than it's fare share of velocities in the ±3 standard deviation
units but "Murphy" is still alive and selecting your cartridges. For
this comparison we may be erring on the conservative side but so what.
The down range velocity variation or velocity variation at 1000 yards is
probability greater than it started out at. The ballistic coefficient
is also mean value and I have not seen anything reported which gives the
standard deviation for a ballistic coefficient, so using the full three units
equally may not be all bad and may actually be more representative of the
actual results at 1000 yards. So with no wind the 155 Sierra Palma
bullet needs ammo with a standard deviation slightly less than 6 to stay
in the x -ring and standard deviation of 11 to stay in the ten-ring.
So much for muzzle velocity variation, what about wind
and wind variation? First constant wind, this is the easy part.
Faster bullets drift less and slower bullets drift more.
Target 2 shows the effect of a constant 20 mph wind at 90 degrees to the
bullet flight. Blowing right to left. The faster bullets drift
less and are high and to the right. The slower than average bullets
are a little low and to the left. Shooting 1000 yards or rim
firing at 200 yards you got to know when to hold them and when to roll them
sight knobs. Target 2 is a perfect machine rest center hold and you
can not make any sights corrections from that angled vertical group.
The only thing you can do is find better ammo.
How good can you read the wind? Plus or minus
how many mph? For slow winds with velocities less than 8 mph and reading
the mirage in a spotting scope maybe ± ½ to 1 mph?
For stronger winds when the mirage cannot be seen in the spotting scope and
you are now forced to read the moving grass, waving wind flags, range flags,
flying debris, and etc. maybe to within 1½ to 2½ mph.
We know the wind does not blow steady. The weather reports state that
the winds will be coming from some direction and blowing between something
and some more something. The reports may even state that there will
gusts up to some really big value.
Target 3 shows the affect of a variable wind on the palma bullet at constant
muzzle velocity. The wind speed could be any velocity, the effect shown
is from the variation in the wind. The top row on Target 3 shows the
right to left drift difference from a wind varying ±0.5 mph.
The second row from the top is ±1.0 mph, while row three is ±1.5
mph and the bottom row is ±2.0 mph. Conclusion: A small change
in wind velocity can very easily move a palma shooter out of the x-ring
or ten-ring. I don't know how good you are at reading wind? But
I don't know if I could tell the difference between 16, 17, or 18 mph wind.
Maybe I could between a 1.0 mph right wind and a 1.0 mph left wind.
This is one trait of a good coach or spotter. To see or have a feel
for the changes in the wind. Now there is also a direction thing
for the wind and you guessed it, it's got some variability also. So
how good are you at directions? Can you tell wind direction changes
to within ±2.0 degrees? A straight away head wind or tail wind
maybe? But a wind blowing at 45 degrees to within ±0.5°.
Now add all this together, i.e. muzzle velocity variations plus horizontal
wind speed variations plus horizontal wind direction variation and what does
it take to hold the x-ring at 1000 yards? But for now we are not going
to think about any vertical wind factors, basic gun repeatability, sight
picture and alignment variations, variable light conditions, or ballistic
coefficient variation. So what does it take besides lots of luck?
Target 4 is a one hundred shot simulation with perfect
holding and sight pictures using the Sierra Palma Bullet with a muzzle
velocity of 2950 fps with a SD=4, wind speed ±0.5 mph, and wind direction
at 45 degrees ±1 degree. The simulated target was scored a 1000
- 100 X's.
Target 5 one hundred shot simulation the muzzle velocity
standard deviation was increased to 9, wind ±1.0 mph and wind direction
at 45 degrees ±2.0 degrees. This simulation was scored a 998
- 32 X's.
Target 6 is at 800 yards with the same variations as
Target 5. It was scored a 1000 - 91 X's. If it holds the ten
ring at 1000 yards it should hold the x-ring at 800 yards.
Target 7 is my expectation for the variations.
Muzzle velocity standard deviation of 14 for the factory loaded ammo.
Average windy day of 15 mph at 45 degrees. Shooter and or coach good
for ±1.0 mph on wind speed and ±3 degrees on direction.
After looking at Target 7, the chapter on "Conditions" in G. David Tubb's
book the 'Highpower Rifle", makes more sense. His discussion on the
wind cycle and staying ahead of the wind are very interesting. Now
you add to this target the variations for light from the passing cloud, the
rifle's repeatability, plus just how good is your hold and the group will
open up more. Simulated Target #7 scored as 963 - 17 X's. For
the stated conditions there are no sight corrections required or possible
for Target #7.
Best of Luck to all 1000 yards shooters. You will need
It.
Larry Medler
anyrange@comcast.net
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July 8, 2003