Ballistics – what it’s mean to the gun in the field.
Over the last fifty years or so
significant improvements have been made in the velocity of rifle projectiles
and this together with marketing has played a key part in the belief that
faster speeds must all so be good for shotgun cartridges.
However the benefits of flat
trajectories due to the significant gains in velocity of a single rifle
projectile have been largely due to better bullet design resulting in lower drag
coefficient and lighter projectile mass.
But today’s shotgun pellet is
still the same little round ball (pellet) of lead (excluding non-toxic) as it
has been for generations of shooters.
Hence with no improvements in shape,
today’s pellets are ballistically the same and subject to the same laws of
nature/physics as they have always been.
Apples and
oranges.
"But studying the literature for my current shotgun
cartridges, the velocity is now 1,450fps or even 1500fps so they must be
better than yesteryears cartridges doing only 1150fps?"
First you have to understand what
you are measuring or not as the case may be.
For some reason (marketing?) we in the UK now
advertise cartridge velocity by stating the muzzle velocity, when in the past
manufactures used the
observed velocity.
i.e. velocity measured over 20 yards which can
be shown to be the striking
velocity at 10 yards.
Hence the apparent significant improvement in velocity, when
compared with cartridges of previous years.
For example #7 shot
A Muzzle Velocity = 1500fps =
Observed Velocity of 1130fps
It also worth stating that to
the best of my knowledge not a single cartridge manufacture has the technology
to measure the velocity at the muzzle.
They “calculate” the muzzle
velocity, which is not an easy thing to do for multiple projectiles at
supersonic speed. In fact I can find no mathematical model to do so.
So muzzle velocities have
always been a guesstimate not an absolute measurement.
But surly the muzzle velocity must
be useful? Ballistically the only
use of muzzle velocity is to calculate recoil energy.
Sensibility.
"Before the trend to publish muzzle
velocity how was velocity specified?"
In the UK for CIP the cartridge
velocity is typically measured at 2.5mters (8.2ft) and this is then used to guesstimate
muzzle velocity or calculate observed velocity.
It is the observed velocity, which is by far
more useful than muzzle velocity but it is slower and does not sit well with the
marketing managers.
But all credit to Eley as
they publish both velocities for example;
Eley First Plastic
Wad 7½ 8, 9
Muzzle 1350 fps and
Observed Velocity 1050 fps
Muzzle 411mps and
Observed Velocity 320mps
What’s wrong with
muzzle velocity.
Nothing if you understand it’s limitations and don’t
think just because cartridge A is a lot faster than cartridge B (for same shot
size and load) that cartridge A will give you a significantly “better”
cartridge able to kill long range game or vermin with small shot size.
For that will just not be true, but you can be sure that all other things
being equal (gun, shot charge mass) that cartridge A will recoil more than
cartridge B.
If you look at ballistic tables (that time has verified,
after all remember we still use the same little round ball) then you will see
that the initial extra velocity at the muzzle is not maintained throughout the
pellets travel to the target. In fact the extra velocity is very quickly lost
(especially for small shot) and hence offers very little benefit to the gun.
Example
#7 shot muzzle velocity 1300 fps
30
yards observed velocity 720 fps and
40 yards 600 fps
#7 shot muzzle velocity 1500 fps
30 yards observed velocity 750 fps and
40 yards 625 fps
So at normal shooting distances the difference in velocity at
the target is insignificant.
So what’s this mean to the gun in the field.
Pattern and pellet energy is what matters to kill humanely.
It is well understood and acknowledge that a pellet energy of
0.8 foot-pound is required to give sufficient energy to penetrate and cleanly
dispatch pheasants, partridges, grouse, pigeon, ducks, hares and rabbits. For
larger birds like geese the minimum is higher perhaps as high as 1.5 foot-pounds
and for small birds like woodcock around 0.5 foot-pounds.
But lets work with the 0.8 foot-pounds.
Can I use a fast (muzzle velocity remember) clay cartridge
for pigeon shooting and save some money?
Let’s
look again at the Eley First #7.5 (2.3mm) shot (example above):
Muzzle
1350 fps and Observed Velocity 1050 ft/s
Then from the observed velocity the pellet energy will drop
below the 0.8 foot-pounds at around 35yards so provided you shoot over decoys
and are happy to limit yourself to say 30yards
(to play safe) then yes any UK #7.5 cartridge with an observed velocity
of 1050fps (muzzle velocity 1350
fps) will be ok regardless of choke.
However us humans can be bad at judging distance and so it
may be more appropriate and humane to use an EU #7.5 cartridge which should have
a UK #7 (2.4mm) shot size.
Then for the same 1050fps (1350fps M.V) cartridge the drop
below 0.8 foot-pounds will be around 45 yards which is a much better all round
decoying cartridge (improved cylinder choke).
But to make a memorable day’s pigeon shooting and take the
long shots and push out past 45 yards you have two choices go faster or bigger
in shot size (1/2 choke).
Going faster will increase recoil and may take you out of the
“cheap” clay cartridge price band in which case you may as well buy pigeon
cartridge in UK size #6.5 (2.5mm) or UK #6 (2.6mm).
For example same 1050fps observed velocity.
For
#6.5 energy drops below 0.8 foot-pounds at about 50 yards
and
#6 at 55yards.
Summary
Hopefully you will conclude from this that muzzle velocity is
irrelevant its observed velocity that counts and unless you have the skill to
reliably hit your target past 55 yards then the need for speed above 1050fps
observed velocity (approximately 1350fps M.V) is not justifiable. If you can
take the long shots then go bigger on the shot size e.g. UK #5 (2.8mm) will take
you out to around 65 yards provided your pattern holds good (3/4 to full choke heavy
loads).
But with a fast cartridge the lead is less, no again do the
sums and you will find the difference is insignificant, what is more important
is you stick with the cartridge you like so swing time (time shot travels down
the barrel) becomes programmed in to your subs conscience.
Remember muzzle velocity is a guesstimate so don’t rely on
it, if need be ask for the observed velocity and with luck if we all start doing
that the manufacture will drop this nonsense of selling by muzzle velocity and
we will know the true capability of the cartridge we are buying.
80 plus yard High Birds - to good to be true?
http://www.shootinguk.co.uk/features/best-shotgun-cartridge-hitting-high-birds-40056
The above makes for some interesting reading – key points.
·
Studying
the literature for these shotgun cartridges, the velocity is now 1,450fps.
·
Hard shot
·
New types
of fibre wads
Where to start !
Again we are talking muzzle velocity (to get an observed
velocity of 1450fps we would need a muzzle velocity of around 2150 fps such a
cartridge has yet to be invented!)
So we have an observed velocity of around 1150 fps for #4
shot
The author is claiming
Ninety yards is within range
For example, I
will use the Hull 32gram fibre No.4 containing 160 pellets, with a velocity of
1,450fps. At 80 yards, the residual velocity of the pellets is 500fps and the
corresponding pellet striking energy is about 1.5ft.lb. Even at 90 yards the
striking energy is still about 1.25ft.lb and therefore should be more than
enough to kill a pheasant.
For #4 shot observed velocity 1150 fps the striking (residual) velocity at:
80 yards is 413 fps
85 yards is 384 fps
90 yards is 357 fps
So not the 500 fps the author claims at 80 yards in fact
500fps striking velocity is obtained at just 66 yards.
Then the pellet energy
• Medium birds
such as partridge and grouse: three pellets, striking energy at least 0.85 ft.lb.
• Pheasants and ducks: four pellets and striking energy from 1 to 1.5 ft.lb
Let’s use my 0.8 ft.lb energy and look at the minimum
effective striking velocity for #4 shot which is 374 fps.
So if the 374 fps is reached at about 87 yards for 0.8 ft lb
then a striking energy of 1.25 ft.lb is not achievable at 90yards (even 1.5ft.lb at 80yards is
unlikely)
with #4 shot.
Yes please, a new type of fibre wad that gives a tighter
pattern to ensure clean kills at extreme range would indeed be good news but to
date I have not found one.
Also current wisdom is, it is the guns choke, not the wad, that
significantly effects pattern otherwise why have a choke?
Pattern
- game over?
The author claims
Let’s assume that
with the right choice of tightly choked, long-barrelled gun and a 32gram No.4
cartridge containing 160 pellets we can achieve an acceptable pattern
(i.e. 120
pellets in a 30 inch circle at 80 yards).
A 36gram (180
pellets) or even a 42gram (210 pellets) cartridge and still get the required
pattern, the extra pellets will increase our chances of a hit. But with the
heavier load there will, of course, be more recoil.
No
we cannot –
Oberfell and Thompson’s book The Mysteries of Shotgun Patterns is recognized
as a significant technical book on this subject and the tables within were
arrived at by shooting thousands of shotgun patterns at varying distances and
gives a pattern percentage for all degrees of chokes for all distances 15 to
60yards.
For
full choke at 60 yards (even with large shot) only 37% of pellets will be within the 30 inch circle so
that is only 60 pellets or half of what the author claims will be within the
30 inch pattern and at only 60yards.
Even
for the heavier 42gm (210 pellets) only around 78 pellets will be within the
acceptable pattern at 60yards (In
fact using the author’s criteria the acceptable pattern is reached at a maximum of
just 45 yards).
Past
60 yards for every increase in 5 yards the pattern decreases by approximately
10% so I will leave you the reader to decide just how very few pellets are in a
30 inch pattern at 80 yards or more.
As
for the comment re long-barrelled gun hinting that it gives some magical
property to the pattern is again unproven barrel length does make a small
difference to velocity but will not put additional pellets into the pattern.
I
hope I have given a little insight to the interesting world of shotgun
ballistics.
As
for shooting extreme 80 plus yards pheasants then if you try and try again then
one must assume luck will at some time plays its part and you will bring down the occasional
bird or is it just another example of our failing to accurately judge distance?
Readers comments welcome.
****
Main text for from the above ** link:-
By Frank Morgan
Last season I
was fortunate to see some fellow guns shooting what I can only describe as birds
at extreme range, and by that I mean higher than 60 yards. And, surprisingly for
me, I was also successful with some of these birds, but I missed a lot more.
What is really interesting is that a few years ago these birds would certainly
have been out of range, so what has changed?
I am still using
the same gun I shot with 30 years ago, a 12 bore English sidelock ejector with
two-and-half inch chambers. I would describe it as a good all-round game gun.
Each year I buy sufficient shotgun cartridges for the season before it starts,
and for several years I have been using the Hull High Pheasant 12 bore range.
Usually I start with No.7s for partridge
and early pheasants, then No.6s and No.5s
later in the season.
Studying the
literature for these shotgun cartridges, the velocity is now 1,450fps, and
hardened shot is used to reduce pellet deformation, resulting in uniform dense
patterns at longer range. So, when is that high bird out of range now?
There is no
simple answer. It depends on the type of gun and cartridges we use and the
target we are aiming at. To find out if a bird is out of range we need to answer
two questions.
1. How much
striking energy of the pellets is required for a clean kill?
2. How many pellets are needed to strike the bird and bring it down?
Thankfully there
are some generally accepted guidelines here and I refer to Gough Thomas’s book Shotguns
and Cartridges for Game and Clays:
• Small birds such as snipe: two
pellets, striking energy at least 0.5 ft.lb.
• Medium birds
such as partridge and grouse: three pellets, striking energy at least 0.85 ft.lb.
• Pheasants and
ducks: four pellets and striking energy from 1 to 1.5 ft.lb.
Ninety yards is within range
For example, I
will use the Hull 32gram fibre No.4 containing 160 pellets, with a velocity of
1,450fps. At 80 yards, the residual velocity of the pellets is 500fps and the
corresponding pellet striking energy is about 1.5ft.lb. Even at 90 yards the
striking energy is still about 1.25ft.lb and therefore should be more than
enough to kill a pheasant. For a 30gram No.5 the corresponding range is 60 to 75
yards, for the No.6 it is 50 to 65 yards, and for the No.7, 30 to 45 yards.
Hard shot and new wads
In practice, to
get reliable results we need to hit the bird with at least three to four
pellets, and to achieve this it is generally accepted that we need a minimum
shot pattern of 120 pellets in a 30 inch diameter circle. A few years ago it was
an achievement to produce reliable patterns at up to 50 yards, but now shotgun
cartridge manufacturers are using new types of fibre wads and hardened shot that
both lead to denser patterns at longer ranges.
We now need to
look at the pattern at, say, 60 and 80 yards using a pattern plate and see how
the pattern varies for different combinations of gun and cartridges. There are
many shotgun cartridges to test but I suggest you avoid plastic wads because
these are now banned on most game shoots.
At 80 yards it’s kill or miss
Let’s assume that
with the right choice of tightly choked, long-barrelled gun and a 32gram No.4
cartridge containing 160 pellets we can achieve an acceptable pattern (i.e. 120
pellets in a 30 inch circle at 80 yards). If the bird is in the centre of the
pattern it is almost certain to be hit by four or more pellets and so a clean
kill will be the result. A near miss potentially resulting in a wounded bird
will occur when the bird is at the edge or just outside the central pattern but,
because there are very few pellets in this outer region, there won’t be that many
wounded birds. It is either going to be a clean kill or a miss. The experts who
regularly shoot birds at this range will confirm this. If we can use a 36gram
(180 pellets) or even a 42gram (210 pellets) cartridge and still get the
required pattern, the extra pellets will increase our chances of a hit. But with
the heavier load there will, of course, be more recoil.
