Faster Isn't Always Better
Why Muzzle Energy Is An Important Factor In Air Rifle Hunting
By Scott Thomas- co founder of Airgun Depot
The airgun industry is notorious for touting the FPS (feet per second) of their
airguns. When we first started Airgun Depot back in 2002 1000 FPS was the standard
for spring powered air rifles. Now we are seeing manufacturers tout speeds up
to 1600 FPS. It seems like every year we see the FPS of air rifles on the rise.
The manufacturers are "keeping up with the Jones'" so to speak, each
one trying to out do the other. Hey, even we get caught up with the high FPS
numbers and use them in our advertising for certain air rifle models. While
there is no doubt that air rifles are getting more powerful as new technologies
come on board, FPS isn't all that it's cracked up to be.
First off, manufacturers use very light alloy pellets when they chrony their
air rifle models. Also,some manufacturers will use the age old trick of dieseling
to reach their FPS claims. If you don't know already, dieseling occurs when you put a tiny drop of a flammable
substance such as diesel fuel in the hollow part of the pellet skirt. When the
supercharged hot gas released by the airgun comes in contact with the pellet
a tiny explosion occurs giving the pellet some extra juice. You can forget about
accuracy when doing this and your airgun will probably die a fast death if you
did this with every shot so we don't recommend it.
So lets take a look at why FPS should not solely be used to judge the quality
/ effectiveness of an air rifle. As mentioned above high FPS numbers in spring
powered air rifles can only be attained by using light alloy pellets, the dieseling
effect, or a combination of both. You may notice that when you fire a break
barrel air rifle rated at 1200 FPS or above with light alloy pellets you will
hear a loud crack. This crack is the pellet breaking the sound barrier. The
speed of sound is around 1100 FPS (it varies with altitude and temperature).
When a light alloy pellet is fired through a magnum air rile it breaks the sound
barrel as soon as it leaves the barrel. This means that the shock wave that
is created will be behind the pellet. However, the pellet doesn't stay supersonic
for long and when it goes sub sonic that shock wave catches up to the pellet
and can cause the pellet to tumble. This greatly affects accuracy and therefore
will affect your groupings. Continue reading
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Now let's take a look at FPS associated with hunting applications. This is
where muzzle energy comes into play. The definition of muzzle energy is as follows:
the amount of energy a projectile contains measured as soon as it leaves the
barrel. The formula for muzzle energy is pellet weight X FPS X FPS / 450240
= Ft. Lbs of Energy (F.P.E) For example, a .177 cal 4.7 grain alloy pellet traveling
at 1400 FPS (Energy= 20 ft. lbs) will have a lot less knockdown power than a
.22 cal 14.3 grain pellet traveling at 1000 FPS (Energy= 32 ft lbs) So in simplistic
terms, the higher the Ft. Lbs of Energy the more knock down power a pellet will
have when it hits a target. Basically a heavier pellet traveling at a slower
velocity will almost always have a higher F.P.E. than a very light pellet traveling
at high FPS.
Generally speaking (if you are a good shot) a 12 ft lb air rifle will have
adequate power to hunt small game such as rabbits but we recommend at least
a 15 ft. lb. air rifle just to be safe. It also will depend on how far away
your target is. Remember, F.P.E is calculated as soon as it leaves the barrel
and then gravity and friction take over slowing the pellet down the further
it gets from the muzzle of the gun that fired it. Heavier pellets will also
retain more of their energy down range. For example if you have a 14.3 grain
.22 cal pellet at 850 FPS and a 12.7 grain .22 cal pellet shooting at 925 FPS
both have similar F.P.E when fired but the heavier pellet will have almost 2
times the knock down power at 60 yards than the lighter pellet will because
it retains more of its energy during flight.
In conclusion, you should always consider the muzzle velocity of your air rifle
and not solely rely on how fast your airgun shoots. This is especially the case
if you are hunting with your air rifle. If you are simply target shooting from
shorter distances the muzzle velocity isn't as big of a factor. A lot of our
customers like PBA ammo for short range hunting and it is pretty effective for
that. Gamo has even introduced a new alloy pellet called the Bullet
which as a longer skirt that is supposed to help with accuracy (the longer the
skirt the more stability the pellet has).
You should always select several different pellets for your airgun and do your
own testing. It's important to find the pellet that your air rifle likes the
best. Also if you are hunting with your air rifle consider how much muzzle energy
you will need to take down your target humanely.
Below are some recommendations from the Airgun Depot staff. If used with the
correct pellet these pellet rifles can generate the proper muzzle energy to
take down small game humanely. We generally find the Crosman Premier, RWS Superdome,
and Beeman Crow Magnums to be accurate in these rifles but be sure and test
a variety of pellets before deciding on which one to hunt with.
As always, have fun and shoot safely.
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