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Sorting out Caliber Vs. Power
(Tossing in Shots per fill as well)
Some of you have asked regarding caliber's
effect IF the foot pounds of energy were equal between ... say
32 and 45 caliber PCPs.
You'll get all sorts of opinions. Since
you've asked me (and this is my site) I'll tell you my experience.
Let's lay out some numbers:
Example 1. Take a 32 caliber slug of
115 grains @ 850 fps and it equals 184 fpe.
Example 2. Take a 45 caliber slug of
215 grains @ 621 fps and it equals 184 fpe.
Now, 99% of the people will jump on
the 850 fps bandwagon (because it's closer to the magic 1,000
fps that all airguns are supposed to dream about). Yep, the trajectory
is flatter. No, it won't deliver as much on-target energy. What
accelerates faster will also slow down faster. And, a lighter
projectile will not retain as much of it's muzzle energy at distance.
In addition, that big surface area
of the 45 slug will offer more of a resistance (read energy transfer)
than the small diameter slug.
So very much of airgunning depends
upon your background. If you come from a background of firearms,
Heaven help you. You'll have spent decades laughing at the guy
at the range who was STILL ONLY shooting 2,700 fps. For you, turning
the dial down to 1,000 fps will be a humbling fall from grace.
Now, if you are fortunate enough to have come from a background
of archery (where all the magazines refer to 325 fps as "Blazing
fast", then winding velocity up by three times will be quite
Actually, neither one matters a whit.
It's irrelevant. Airguns are not firearms, nor are they bows and
arrows. They are airguns. They function as airguns function. They
are limited by the physics of expanding air. So, depress yourselves
or become giddy, no matter ... airguns function as the rules of
physics allow. Some few will become intrigued by learning how
airguns function and develop the skills required to adequately
use airguns. Others will forever be depressed and hope against
hope that the next time they ask regarding velocity, the numbers
will be higher. "Maybe next year's model" will be able
to cheat physics ... but ... I doubt it.
What I attempt, as
an airgunsmith, is this: To use the rules of physics to project
the most energy (with air) to the greatest distance, and with
the greatest degree of accuracy. That's
the ultimate from my point of view. Now, there are many other
schools of thought which raise individual parts of the equation
above the rest. The "velocity rules" school finds they
must cut way back on the weight of the projectile to off-balance
the equation so the velocity portion wins. The "energy rules"
school finds they must fire a very large projectile from a very
large caliber and consume huge amounts of air doing so. You'll
hear of guys jamming huge slugs in some of the Philippine brass
rifles or popping out big caliber ball from converted production
pistols. The velocity numbers are often in the 300 fps range in
order to make the power numbers rise.
I make shoulder fired rifles. Compromises
must be made along the way. There is so much you can do with the
energy which may be stored aboard a reasonably sized rifle. And,
this brings us to "shots per charge" .... again. A choice
is made. More shots at a lower energy level, for a given storage
of air. OR ... less shots at a greater energy level, for the same
given volume of air. No magic involved. Efficiency of design will
help ... yes ... but not to the degrees most people think.
Folks who are interested in big bore
airguns will know of the few commercial offerings in the field.
I have a customer waiting for one of my rifles. He also owns two
of the Korean rifles ... a 9mm single shot and a 45 single shot.
The other day he sent me some velocity numbers and shots per charge
data. I appreciate hearing from all of my customers who share
their shooting stories. He won't mind me sharing some data here.
He's not under any impression that his rifles are delivering state
of the art power, though they are well worth the money and quite
enjoyable. Let's look at a summary of the information he shared:
Both of the rifles filled to 3,000
psi. Both delivered about 18 shots. WOW! The more the better I
always hear. And, can you imagine that for some of my own rifles,
I only quote 3 shots onboard? I must be a really lousy Airgunsmith!
..... (I heard that .... ;?)
So what's the scoop? Well, these rifles
were firing their projectiles in the 500-600ish fps bracket. Over
the 18 shots, the velocity varied maybe 130 fps. The 9mm was putting
out 74-118 fpe and the 45 was making 100-147 fpe. Now, my customer
wasn't bragging about the number of shots, however; I've heard
it from many other people for years. Those folks who are bragging,
don't seem to understand (or are conveniently forgetting to mention)
the very low velocity numbers; and thus the low power band of
their rifles. When I make available state of the art performance
(at power levels of 235+ fpe in 32 caliber, 500+ fpe in 45 caliber,
and 650+ fpe in 57 caliber) I must burn fuel to give it. Thus,
my 45 caliber that actually offers 1,000 fps velocity, does NOT
get 18 shots per fill. And, the rifle that offers a string of
shots within very close velocity tolerances, is doing something
quite difficult. Lastly, the rifle that offers you relatively
high energy at a much lower than commercial psi fill pressure
is doing something quite unique as well.
Maybe this little word picture will
put the final frame around the phenomena. Let's watch two kids
arguing about who has the most money: One has five quarters in his pocket. The other has
twenty pennies in his pocket. It's often
the kid with the pennies who loudly proclaims he has more money.
And, he does indeed have more "money" ... just of a
much lower potency.
So, I make many different rifles. It
depends upon the need of the client. I can cover you up with shots
per charge if you'll take less and less energy per shot. I can
give you that big ole bulging pocket full of pennies. Or, I can
give you a handful of quarters. Your choice. While that's rare
enough ... you also have the choice of some of my work which will
even give you a couple of half dollars!!! ;?) Those are magnum
powered versions of each caliber, which are designed to give you
the best possible compromise of velocity and power projection
for their individual calibers.
OK ... coffee's gone. Back to the shop.