In the last article [Air weapons and the need for speed] I briefly spoke about the kinetic energy of a projectile i.e. how hard it could hit depending on its speed and weight. This was a lead in to the age-old question what is better, a large heavy projectile with loads of knockdown power, or a lighter FASTER projectile with plenty of penetration.
Most common air weapons come in one of 4 calibers.
.177″ (4.5 mm) , .2″ (5 mm) , .22″ (5.5 or 5.6 mm), and .25″ (6.3 or 6.4mm).
All have their specific uses, their followers, and their critics.
To calculate how hard a pellet will “smack” something is a complex thing over range because of the varying shapes and sizes causing variable drag and loss of power although you can work out accurately what it will do when it is just leaving the muzzle.
Wanna know the formula?
First you’ll need to know the weight of the bullet / pellet.
All bullets and pellets are measured in grains.
In conversion terms:-
7000 grains = 1 pound (453 grams)
437.5 grains = 1 ounce (28 grams)
1 grain = 0.0023 oz (0.065gm) Kinda small isn’t it?
The formula goes:-
Here is an interesting thing to ponder. Something I read somewhere. If the muzzle velocity is 671 fps, the weight in grains is the power in ft-lbs. It works because 671 x 671 equals 450241. So at that speed, a 11 gn slug develops 11 ft-lbs and a 30 gn slug 30 ft-lbs. Anyway I digress.
What’s the power of smack got to do with penetration?
To enter the skin takes power and to burrow deeply needs power and a “pointy” non deforming tip. Except there isn’t a lot of power generated with an air weapon using diabolo style pellets.
Typically the most you will achieve is 50-55 ft lbs and comparing that with a regular 40 gn 22 LR which generates 104 ft-lbs things look pretty weak. I’m not going to repeat myself about these differences, and I’ve discussed this in the post [22 LR v Air Rifle].
Hunting wise it takes the minuscule force of 4 ft-lbs to enter the skull of a rabbit and only 2 ft-lbs for a small bird.
As for a human eye?
If the pellet is moving at a speed greater than 230 fps, it can penetrate. (15 gn @ 230 fps = 1.75 ft-lbs).
Always wear shooting glasses folks!
Penetration is a function of energy transfer so if a pellet EXPANDS DRAMATICALLY as it hits, it will transfer more energy in shock than it would by penetrating deeply. It also follows that pointy harder pellets will burrow more deeply than soft, dome or even hollow point ammunition.
A note about hydro-shock aka Hydrostatic shock.
What we are talking about is the massive shock wave exerted on the cardiovascular system when a firearm bullet and the accompanying pressure wave ploughs its way into a body. For example, a chest strike may massively pressurize the body to such an extent that it may literally blow out blood vessels in the brain and other organs.
Having said that there are some “experts” that don’t agree with this theory.
Good news! (Sort of).
An air gun pellet in the above calibers is unlikely to achieve such pressures although a hit on a vital blood vein or artery could cause a catastrophic loss of blood or enough shock to stun or cause massive swelling to a blood vessel thus restricting blood flow.
Not very useful BUT shoot at a person and hit them just right?
Enough said about that.
Why does everyone go on about penetration and small game?
Is there a need to burrow deeply?
Take shooting rabbit.
The distance from ear to ear (a side head shot) is typically 32 – 35 mm ( 1 ¼” ) for a juvenile, and up to 39 mm ( 1 ½” ) for an adult.
Take shooting Canadian Geese.
The width of a skull is approximately 40 mm. ( 1 ½” )
A domestic cat.
Ear to ear, 60 mm ( 2 ½” ) BUT that’s one strong skull and the brain is more complex so takes a LOT MORE KILLING.
Now about that question of wanting LOADS of penetration?
Does anyone DISAGREE that anything up to 2 inches is plenty enough for small game?
I used to pest control with air weapons.
One of the most difficult of venues was in a warehouse or office.
For the most part the “prey” was feral pigeon and rats yet the problem was over penetration causing damage to the fabric of the structure.
The POWERFUL air weapons were ditched in favor of lighter “Crossman” style weapons.
Developing just 4 ft-lbs (346 fps) at the muzzle with a couple of pumps, and over 50 feet maximum, the little .177’s (shooting heavyweight 15 grains / 0.975 grams) REALLY SOFT domed lead proved the way to go.
The shock of impact being enough in most cases. So little penetration, loads of “knockdown power”.
Have I answered the penetration question though?
Well sort of but I should state that I’m more a fan of knock over power than penetration.
Rabbiting again. Night after night I’d happily clear bunny with my 12 ft-lb rifle with its 21gn dome headed pellets. One shot, one kill.
Occasionally we shot with others all using .177 and boy did they have problems! With rabbit receiving a clearly audible “smack” as the pellet hit the chest cavity, they (in most cases) just hopped away as though nothing too adverse had happened.
A couple were field dressed by me and apart from those where the heart and lungs were penetrated, a slight miscalculation would do internal damage (of the unrecoverable without surgery type) injury with the “through and through” type of injury professional hunters hate. Add the gut shots and I’m pretty certain some rabbit had lingering deaths.
Without kinetic shock, a bunny usually just keeps on hopping.
A bit different when it got hit hard by a .22 soft-nosed pellet.
Even if not fatal, the bunny would be bowled over by the heavier harder hitting .22 and stunned for a few moments, long enough for a reload for a safety shot or for you to walk across and dispatch the bunny to its heaven.
Field dressing these animals found LOADS of internal disruption of organs, a massive blood loss and, just like humans exhibit, accompanying sudden if not fatal shock.
Back to penetration.
A question for ex-mil.
What do you prefer?
5.56 mm and watch someone keep on coming or a 7.62 mm (be that 51 mm or 39 mm) and them KNOWING they have been hit. Interesting one that. Garden gun ammo or a heavy hitting .308 / 7.62?
I won’t bother asking about 50 cal.
The ultimate “sit quietly over there and die” type ammo.
Ultimately penetration isn’t a priority of mine.
Energy transfer is and extremely “squishy” soft-nosed ammunition is my idea of a “safety” ammunition.
A note has to be said about hollow point air pellets. WHY?
Beneath 30 ft-lbs the so-called “air burst” or super deformation and stopping power from the hollow point just doesn’t work. At best the hollow point lends itself to expansion on impact with air weapons but not a lot different from a soft domed pellet.
However filling that cavity with something REALLY nasty like Ricin has its appeal. As for comparing the physical effects of a hollow point firearm round to an air weapon pellet?
That’s rather like comparing chalk and cheese for taste.