Foot pounds energy in Air Rifle

Normally, in ballistics, you would use the muzzle energy. 12 ft-lb sounds a little high for a Red Ryder BB gun. It's only important to have enough that "You could put your eye out!".

Ah...I didn't make it clear... I know the figure is correct.. it's just the units that strike me as odd.

just to stir any potential controversy he chose a .177 over the .22 on the grounds that at the same energy the .177 would have a higher velocity and hence flatter trajectory...
I'm sure he's had a few arguments in the pub over this choice .

Del

Oh surely (and yes, I will call you surely) you're not gonna bring up that poundal vs slug thing again, are you? You guys convinced us to go with feet, pounds, and guineas instead of the French meter and Newtons; then you abandoned us.

The velocity vs mass argument is timeless and probably not ever to be settled. I always used a 12 gauge, #7 shot for pigeons.

then you abandoned us

In my history lessons it seemed that we didn't leave voluntarily, but were forcibly ejected*. You were hardly "abandoned"...

*Them Frenchies had a hand in that too...

Del, you always have to remember that when we talk in feet, pounds, and BTUs that your pound unit is a fraction of a Euro, which tends to complicate things. So, if we use foot - Euros, does that help? It helps us to include the value of the weapon in our calculations. The value foot-Euros can be converted to pound - pounds for simplicity.

Well, of course the American has to come in for the rescue...

Ft-lbs is not length times mass, it is length times force.. In this case lbs force not lbs mass, and indeed in our beautiful system of units which we of course refer to as "customary" the lb is most often used for force as slugs are more typical mass units (as well as being slimy creatures that are essentially snails that somehow lost their shells).

Bottom line is that ft-lbs is the customary unit for torque, which can be related to power.

Further proof that the UK has not completely given in to SI, and that America is not the last bastion of "customary" units

(although I am not endorsing ft-lbs as a good unit for energy of an air rifle, that is just barmy.)

So where does it get the foot and where does it get the lbs value from if we talk about a riffle?

I am just very confused about this. I always fight with the keepers of the imperial bastion about how incredibly daft it is to hold on to something derived from the anatomical measurements from one of your ancient kings but I do know most of the ways it works in ( that I need for work or hobby) and this one seems a bit off the mark so to speak.

Please elaborate and maybe after that we can discuss the various ways to cook pigeon breast although I would have thought you a proper cat and eat it "au naturel".

In terms of testing air rifles I think they just calculate it from muzzle velocity and projectile mass.

I was amazed that something enshrined in legislation could be in other than SI units.

I wonder what the force in an arrow from my longbow is???

I often get a nice bag of pigeon breasts when I see my Bro' but not this time.

It seems if I wanna get more breasts...I just have to increase the force in my muzzle don't I?

That is a normal (if old fashioned) description for energy, I also believe that the .177 pellet will travel faster and is effectiver at longer ranges than a .22, I used to use both....

I even used to use a Crossbow (and tuned up air rifles) for Pheasants/Partridges etc in our UK garden and I used Fiberglass bolts with the metal tips removed (otherwise they might have gone too far for safety if I had missed!!!). My neighbor used a shot gun!!! Luckily our hedge was very thick!!

The 12 Ft/Lbs can be expressed in Joules of course, which would be about 16.26981 Joules.

A good page for conversions of various types is at the following:-

Conversion Formulars

You guys got it right. It's muzzle velocity in feet per second times the projectile weight in pounds. And, yes, I would also choose the .177 over the .22 given the 12 ft/lb limitation.

Nothing can argue with my 12 guage. I have many weapons. 30/30, 30'06, .22, My uncle left me a 1932 over/under 12 guage Savage, made right next door, in Springfield, Massachusetts. I use it all the time, but just for clay pigeons now.

I thought all Bank holiday's where on a Monday?

Hey Bricktop, I have a Savage over/under as well. Mine is a .223 and a 20 gauge. It's a decent deer/turkey combo gun.

20 ft lb is amount of energy needed to raise a 1 lb weight 20 ft (or a 20 lb weight 1 foot) etc. Power is energy per unit time.

Whoops ..yes I was sloppy too I meant energy not power....

No one seems keen to answer the question...
Basically is 'pound' a measure of mass or force...? I believe technically it's mass, and 'pound weight' or 'poundal' is force.

But WTH I got energy .. power wwrong...maybe I should just curl up and have a nap.

Del

"No one seems keen to answer the question...
Basically is 'pound' a measure of mass or force...? I believe technically it's mass, and 'pound weight' or 'poundal' is force."

I did! It is a measure of force!

Why are you asking us? We wanted to go with mass in beads, distance in moccasin length, and time in moons, but no, you guys had to send General Gage over here to whip us into shape. To this very day I have trouble converting shillings into beaver pelts.

Ok I come clean before I even start here, I contemplated posting this reply as a guest as it is very embarrassing ok.

First time I ever used a torque wrench, it was one of those long ones with a bendy bit and a needle on a scale at the handle thing, I was torquing up my valve rocker blocks of my beemer boxer. I had done the head conversion to a lead free type and with better fitting over sized pistons (old bike so worn a bit). I misread the scale and used the wrong scale which resulted in grotesquely over tightened rocker blocks.

First start was fine and absolutely no problem for the 20 odd miles I did with it but then I stopped and had a cup of coffee at my mates house. An hour or so later i was going to go back home but the bike would not start. My mate helps to push start the thing and after some time it did go but it had a afterburner flame of about 2 meters out of one pipe and my mates trousers were black. The bike seemed to run on 1.5 cylinder so I limped home on it. When I took it apart, the rocker blocks of the left side cylinder where literally flattened by the torque and I had to replace rocker blocks, rocker shaft and the cylinder studs as well as heli-coil one stud thread in the engine block. Small mistake big consequences. Think twice and do once is now my motto.

OK, but that still doesn't answer the question of how many gills of water there are in a pound?!? But other than that, I broke down and gave you a GA vote (actually to both of your answers...). Now, as to those gills...

So the unit is wrong! Somewhere along the lines of the calculation the seconds have been lost.

Unless the pounds you mention is actually lb_f which is the exerted energy unit from long ago. You are right Dell, it should have been updated to Newtons.

This is why we have the industrial standards, so there will not be any confusion over it.

I think you will find many of these little "gems". They still say psi don't they?

They taught us way back in Basic Engineering that the work done on an object was equal to the change in kinetic energy which would be seen by that object... There is also the impulse - momentum relationship. As I remember (it was over 30 years ago) there was a derivation of both relationships.

So if you integrate the area of the bore times the length (to get force) times the length you get ft lbf as the work done on the projectile which will equal its change in KE.

.177 vs .22 177 does give higher velocity and I seem to get better penetration at short ranges anyway. At long ranges the .22 seems to retain more velocity and performs somewhat better...

I'm not sure I've ever seen an air rifle specced in therms of ft-lbs, here in the US they usually only give the muzzle velocity in feet per second (FPS). If the above calculations are correct, 800 FPS to keep you under 12ft lbs sounds weak. I had one as a kid that was around 1400 FPS and we (my childhood friends and I) used to run around the woods shooting each other.

I hope the UK pigeons are better then the US ones....they're the rats of the sky here...

Avery Montembeault

The old Daisy guns were specced at about 5 ft-lb. They probably were worried about shooting Little Beaver's eye out. When the multiple pump guns became popular (sometime in the 1950s), they went a lot higher.

Not relevant at all, but I just looked up some energy figures for longbows....

33ft-lb would seem to be about what I'd get from my longbow...
So if you get the choice of being shot by an air rifle or a longbow... chose the air rifle .

Del

What would that convert to in 'muzzle' velocity, any idea?

Damn..I'll have to get my books out again...

About 180ft/sec for a target arrow....

12 foot pounds .....

Is that how many times you'll jump after you get shot? Or stomp your feet 12 time?

I remember the max energy in J when I was back in HK. Don't remember the number but I know the .38 the cop use is just above the limit.

Hello Del

a) Presumably it's in UK, so yes you would expect it to be in joule, 16.27 joule since you ask.

b) you're right, it's a measure of energy. Should really be ft.lbf (lb force). But not poundals. Poundal is force to accelerate 1 lb mass at 1 ft/s², and = 1/32 lbf (taking g = 32 ft/s²), but you don't hear much about it these days. Other approach is to keep the lbf as force unit and define a mass, the slug (= 32lb), such that 1 lbf accelerates 1 slug at 1 ft/s². As we try to be metric in UK, we don't hear much of that either, I don't know whether they use it over the pond, or just use lb mass and lbf and put g in formulas to get the right result.

I suppose 12 ft.lbf is the energy in the pellet (as opposed to in the compressed air)? If so, and taking 1 gram for pellet mass, it comes to 180 m/s or 400 mph, which seems about right.

Cheers.....Codey

I don't know whether they use it over the pond,

Yes, we slug people around often. Only a few countries can outdo us in violence.

I use slugs all the time in aerodynamics and hydrodynamics. By doing so, the various formulas "make sense": if you want SI units you can just swap them in. Lbf and lbm is just too weird for me. Even weirder, in my view, is kgm and kgf. When you already have clearly defined units that are in common usage why throw a spanner (wrench here) in the works?

I suppose 12 ft.lbf is the energy in the pellet...

Let's see... I know the formula for that: E=MC². Don't get near me with that pellet!

Found this:-

http://www.airguns-online.co.uk/you_and_the_law.htm

UK Legal Limit

To calculate the power of an airgun you need to use a chronograph to measure the speed of the pellet (in feet per second) when fired, and you need to know the weight of the pellet in grains. Once you have that information you perform the following calculation: - speed (ft/sec) X speed (ft/sec) X weight (grains) 450240
this gives you the result in foot pounds force (ft-lb).
As mentioned the legal maximum for an unlicensed air rifle is 12 ft-lb which from changing round the above formula, gives the approximate values as follows:-
A .22 pellet weighing 14.4 grains, maximum permissible speed is 612 ft/sec
A .177 pellet weighing 7.9 grains, maximum permissible speed is 826 ft/sec
The corresponding figures for a pistol are 433 ft/sec for a .22 and 584 ft/sec for a .177
The pellet weights used in the above calculation are typical weights for the sizes of pellet but you must always check the actual weight of your pellet before performing your own calculation.

WOW! Pretty sophisticated for the above average user. Even more so for the average Joe.

Isn't this something that would typically be done by the manufacturer?

What you need to get for your brother, possibly for Guy Fawkes day, is an old Chesapeake Bay goose gun. They were 8 gauge shotguns, with barrels roughly 6 feet long and trunnion mounted (unless you had a really strong, really stupid brother-in-law to hold it), and were loaded with BB shot.

He has restored 4 bore punt guns and has an amusing anecdote ... 'The indoor punt gunner'
I expect you can figure it out yourself...but in involves a hole being blown in a wall .

Del

OK, I'll bite - what is/are "4 bore punt guns"? It sounds like a four-barrelled boat-mounted fowling piece, but etymology seldom if ever works that way...is it more like this:

???

It's a single barelled boat mounted fowling piece. 4 bore... is a big bore... 4 balls of that bore would weigh a pound...same way that a 12 bore is so called because 12 balls of that bore would weigh a pound.

Del

QUARTER POUND CANNON BALLS?!? What kind of "fowl" do y'hunt with something like that? Seems extreme even for ostriches or emus. Moas? Elephant birds? But they went extinct pre-gunpowder... I'd pick it for big game in Africa, maybe, but crikey!

QUARTER POUND CANNON BALLS...

No it fires shot!...the ball thing is just how the bore (gauge or is it gage? to you folk over the pond) was measured in days or yore..

Del

Here it is gauge - nowadays, a 12-gauge (12 ga abbreviated) is about as big as you can normally find, and is used for ducks and geese. Or with slug loads, deer and elk.

How MUCH shot, and of what size? To me, the thing sounds like an artillery piece, not a hunting gun! And if it's four balls to the pound, how do you fit them in the barrel to figure the "bore"? Side-by-side seems way huge, but end-for-end wouldn't be so much over-sized. In which case, why have four? I still think this is the smooth bore version of the express rifle b'wana used to use on these guys...

You're all looking at the technicalities from the wrong end. All shooting problems derive from shooter's thrombosis, which roughly translated means the clot holding the gun.

Simon

ex dogshit expert Shooting Times.

I think this is the actual gun my Brother restored.. I know he sold it at auction and it looks like the one...he had to re-engrave the underlever and a fair bit on the lock. . He did a nice tudor rose where your thumb works the underlever. I remember saying he only had 4 or 5 cartridges for it as thay are hand made of brass and are re-loaded...you won't find 4 bore shells over the counter!

Del

"...you won't find 4 bore shells over the counter!"

I wouldn't wonder - did some research. Those things were outlawed (albeit still used, I'm sure) in the US just before WWI. Game conservation laws made market hunting illegal, and who would need something said to be able to kill 100 birds per shot just to feed the family? You can still buy the shells at auction or (as seen here) on eBay:

Del...heeere kitty kitty. Look at what I found today while looking for something else...

http://www.youtube.com/watch?v=ltQeCrVJtLU

You're gonna LIKE this I bet...

So that is how they killed off the passenger pigeons! Maybe I can get one for the blackbirds that are dominating my bird feeders and giving me dirty looks.

You are not thinking this through my friend!!

That is the way the diameter of the guns bore is measured only, it actually fires shot, probably BB size or maybe bigger......although I have never been Duck hunting with such a gun, only read about it!!!

If someone is told he is a "Bore", does that imply that his Testes each weigh 1 lb?

Only if he has four of 'em, I think...

...walking must be a problem!!

I can only imagine...

Foot pounds of energy for an air rifle or air pistol are calculated as follows:

mass of the pellet (in grains) x velocity in feet per second squared

divided by 450240.

Same works for bows, atlatls, blowguns, slingshots, firearms, etc.