Power level of of Airguns & associated factors

[Sujay]

I request some information on power levels of Air Guns, particularly possession of which needs an FAC in UK. Here I go....

1) The legal limit for Airguns not requiring an FAC is 12 ft lbs. Now to increase the power, a powerful / special spring is required. Is only a spring sufficient ? Nothing else ? What is the fps equivalent of ft lbs ?

2) The spring is installed and the power level goes upto say, 30 ft lbs. Is the relation between ft lbs and fps linear ? If not , how to arrive at the equivalent fps ?

3) A Specific V Mach tuning kit is available for FAC rated Air Rifles.

a) Why should an FAC rated AR need V Mach tuning kit ?

b) If it needs the kit, then the V Mach tuning has nothing to do with
power . It is more of a refining tool. Right ?

3) What does this statement mean .." Smoother, quicker, sweeter, more accurate, more refined, better mannered..." Really ? Sounds straight from a script ! Somebody please explain this to me, a novice.

And if somebody knows links to these subject, please provide them.

Thanks.

Sujay

[Mack The Knife]

Tomorrow. I am off to bed.

[Grumpy]

Just changing the spring of a 12 ft lbs rated air rifle won`t increase the energy to 30 ft lbs - a lot more modifications/work is required. Many models of spring-powered air rifle won`t make 30 ft lbs no matter what you do to them - they`ll make c.17-18 ft lbs max.
The Guru Dodger will pronounce tomorrow - he`ll tell you all about it.
The formula for calculating energy in ft lbs is :
E = M multiplied by V squared divided by 450437
E is Energy in foot pounds ( fps ). M the mass of the projectile in grains ( gr ) and V the velocity of the projectile in feet per second ( fps ). 450437 is a constant which allows for the convenient calculation in ft lbs. A grain is 1/7000 of a pound ( lb.)
From this you should be able to see that the relationship of the velocity to the energy is not linear but logarthymic.
eg. A .22 lr 40 gr bullet travelling @ 1100 fps produces approximately 107 ft lbs energy. If the velocity is doubled the energy produced is four times that amount.
If the bullet or pellet weight is expressed in grams then it is much easier to use the metric calculation for energy in joules which is:
E=1/2MVsquared.
E is the energy produced in joules. M the mass in Kilograms and V the velocity in Metres per second.
1 foot = 0.3048 metres. 1 joule = 0.737562 ft lbs.

[Mack The Knife]

The legal limit for Airguns not requiring an FAC is 12 ft lbs. Now to increase the power, a powerful / special spring is required. Is only a spring sufficient ? Nothing else ?

What really determines the maximum power potential of a spring-piston air-rifle is the swept volume of the piston within the cylinder.

Certainly, a more powerful spring has its part to play but you will also need to increase the piston weight. Rather than make a new piston, DIY kits come with preload washers that are added to the piston.

What is the fps equivalent of ft lbs ?

Do you mean what is the muzzle velocity of an air-rifle producing X ft.lbs. of muzzle energy for a given calibre and pellet weight?

If so, the general rule of thumb is:

.177" calibre: 800 ft./sec. = 12 ft.lbs.
.22" calibre: 600 ft./sec. = 12 ft.lbs.

This is assuming 8'ish grains and 14'ish grains pellet weights in .177" and .22" calibre respectively. This is only an approximation.

The spring is installed and the power level goes upto say, 30 ft lbs. Is the relation between ft lbs and fps linear ? If not , how to arrive at the equivalent fps ?

The only spring-piston air-rifle that comes close to 30 ft.lbs. is the Webley Patriot and it does that at the expense of a very harsh recoiling cycle and accuracy. Never buy this rifle unless you know how to tune it.

E = M x V x V / 450240

E : Muzzle Energy (M.E.) in ft.lbs.
M : Weight of the pellet in grains.
V : Muzzle Velocity (denoted as M.V. or Vo) in ft./sec.

(Grumpy, why you are using the constant 450437 instead of 450240? I know it varies depending on height above M.S.L. (I think), just interested in knowing how you arrived at it.)

Why should an FAC rated AR need V Mach tuning kit ?

It does not have to have a V-Mach tuning kit. There are quite a few other places that make tuning kits or sell seperate components. However, Venom's components are amongst the best in the market, if not the best. So, if you want the best for your air-rifle, buy from the best.

If it needs the kit, then the V Mach tuning has nothing to do with
power . It is more of a refining tool. Right ?

The kit provides both with the bias in favour of refinement. For example, I could buy components that could take my HW80K to 23 ft.lbs. rather than the 20 ft.lbs. that Venom offer but at the risk of turning a refined air-rifle into an unrefined one.

What does this statement mean .." Smoother, quicker, sweeter, more accurate, more refined, better mannered..." Really ? Sounds straight from a script ! Somebody please explain this to me, a novice.

Smoother to cock.

Quicker: Faster lock time because the tolerances of the components are better.

Sweeter because there is no spring twang or jarring.

More refined and better mannered: These are the result of the above.

All of the above is immediately noticeable on shooting a Venom. If you come to Bangalore, I could arrange for you to shoot a standard HW and a Venom tuned HW. Shoot both and you will realise there is no snake-oil involved in any of these claims.

If you are contemplating buying one, stop contemplating and just buy it.

Mack The Knife

[Grumpy]

That`s a really good question Dodger......and the answer is that the 450240 constant is out of date.
The gravitational constant used to be accepted as 32.16 which, when `massaged` to provide the constant used for calculation of energy in ft lbs, gives the denominator 450,240 however the ISAO Standard for the gravitational constant has been set at 32.1742 for several years which provides for the energy constant as being 450,437.4.
Firearms types are generally conservative and the adoption of the `new` constant has taken some time but most now accept the revised constant........or rather; Most of those that are AWARE of the revised constant now use it.

[Mack The Knife]

Grumpy,

Thanks a lot for the explanantion. Got to rush again.

Mack The Knife

[Sujay]

Thanks a lot gentlemen

Now it makes a lot of sense; particularly after knowing the actual role of the tuning kit. Now I would do a bit of 'Knowledgeable surfing' instead of ogling.


Thanks Again !!