H&S - making sure demonstration equipment is safe?

[winchman]

I hate to be a killjoy, but aren't you being asked to build a barreled weapon? 42mm keeps you under the 2" limit for smooth bored cannon/shotgun but if you are over 12ftlb muzzle energy I'm guessing that would class it as a cannon and put it into section 2.

That's a good point that must be considered and checked before you build.
You will find with your insurance etc that they will want to see some evidence of a pressure test usually a static and possibly a working test and annual inspection to ensure its safe. I personally would not consider a second hand pressure vessel unless it has had an inspection and is certified.

 

[julianf]

in order to exceed the 12ftlb limit he would need to be launching the balls at over 130kmh; that's quite an ambitious target.

The ft/lb figure is a function of both velocity and projectile mass.

A 58g tennis ball would have to be travelling at 204mph to get to the 12ft/lbs limit.

We were looking at squash balls, which are less than half the mass, at 25g.

If my sums are correct (?) then that requires a muzzle velocity in excess of 300mph to exceed the 12ft/lb limit.

If the above numbers are correct, i dont think that (specifically - as in firearms legislation) is of concern.


That said, my numbers dont seem to tie in with the figures above, so one of us has made a mistake - could well be me (?)

 

[wyn]

That looks about right............25g at 316 mph (464 fps) would be 12ftlb

 

[Fergus]

That looks about right............25g at 316 mph (464 fps) would be 12ftlb

You are mixing grams and grains for your mass measurements. A 16 grain (1.03g) air pellet travelling a shade over 600fps is knocking on the door of 12 ftlb

A 25g ball weighs 385.81 grains so travelling at 464 fps has you knocking on the door of 185 ftlb, more power than any of the .22lr rifles on my firearms certificate. To stay under 12ftlbs with the squash ball you would want to top out at 118fps or just over 80mph.

 

[Fergus]

My mistake the "g" should have been "gr"

It's an easy mistake to make, I'm a child of the 70's so permanently confused with weights and measures.

 

[wyn]

Yes, i was thinking grains not grams

 

[Gareth J]

A friend of mine took his potato cannon we made from bits of sewer/drain pipe into work (he's a secondary school physics teacher) and fired it in the playground with lynx Africa he got from one of the kids. All was fine but I was mortified when he told me. It's good that you're thinking this through. My vote would be a fire extinguisher or small water pressure cylinder, both seem about the right size, cheap enough, pressure rated and come as standard with bsp threads.

 

[Justme]

in order to exceed the 12ftlb limit he would need to be launching the balls at over 130kmh; that's quite an ambitious target.

Not so. Any projectile could be used to test it for its power. Just like an airgun that could be under 12ftlb with your pellets but over with the ones used in the police lab. You still get nicked.

 

[Justme]

Check THIS out.

 

[doubleboost]

This would do your job
Tested complete with high flow valve
http://www.tyrebaydirect.com/56-Tyr...ng_Tyres___Bead_Blasting___25_litre.html?si=1

 

[captain-destructo]

This would do your job
Tested complete with high flow valve
http://www.tyrebaydirect.com/56-Tyr...ng_Tyres___Bead_Blasting___25_litre.html?si=1

one of them would get you around a lot of problems
change the outlet tube for one the correct diameter
change the inlet connector to a tyre valve
and the pressure relief valve downrated so they cant build the pressure up too high and kill some one with it

 

[julianf]

In follow up to this -

The prototype needed to be dismantled. We hooked up some light gates to the muzzle, and the results were of some concern.

I guess it could be built with a rated tank, and relief valve, as above, but i think things have moved on now.

Thanks to all for their input, and im sorry i cant follow up with a more positive conclusion.

 

[penfold]

Not so. Any projectile could be used to test it for its power. Just like an airgun that could be under 12ftlb with your pellets but over with the ones used in the police lab. You still get nicked.

12ftlb(16 joules for the youngsters out there) is a force; the projectile doesn't matter as long as the amount of kinetic energy is <12ftlb, it could be a football or a pingpongball or a grain of rice. Dibble changing what pellet they stick up the pipe won't change the muzzle energy because it's a product of the muzzle velocity squared multiplied by half the mass; if they get tricksy and use a lighter pellet the chrono will show a higher velocity but the energy will remain constant(within an error band).

 

[Justme]

12ftlb(16 joules for the youngsters out there) is a force; the projectile doesn't matter as long as the amount of kinetic energy is <12ftlb, it could be a football or a pingpongball or a grain of rice. Dibble changing what pellet they stick up the pipe won't change the muzzle energy because it's a product of the muzzle velocity squared multiplied by half the mass; if they get tricksy and use a lighter pellet the chrono will show a higher velocity but the energy will remain constant(within an error band).

Whilst your reply might be partially correct it totally misses the point.

With an air rifle the weight of the pellet affects the speed of it.

Springers give more power with a lighter pellet & PCP's with a heavier one (I think I have it the right way round).

So if I set my PCP up with a light pellet to 11.99 ftlb & the plod test it with a heavier pellet it will be over 12ftlb. Even though the speed will be slightly lower on the heavier pellet. The output does not stay the same with different pellet weights. Its a well known problem.

 

[penfold]

If they can provide a NPL ticket showing their chrono has been tested to that level of accuracy I'll eat my hat! I confess I was unaware that there was variation to that degree though.

 

[Justme]

Most cronos are very accurate. I am sure that plod would only use ones that are approved for court use.

The thing is with a possible 8+ grain (so about 50% variance from lightest to heaviest) difference in weight even a non accurate crono will see the energy difference. The weight of the projectile make a huge difference to the energy it contains. Your ping pong ball or grain of rice would need to be supersonic to have the same energy as a football thats just been kicked.

A 12 grain pellet traveling at 670fps has 11.96ftlb
A 16 grain pellet only needs to do 580fps to get the same energy. At the same fps its doing nearly 16ftlb.

When testing my PCP (from memory with pellets from just over 11 to under 18g) the fps only varied by a small amount from the lightest to the heaviest pellets. Once I found the ones that suited the riffle the best the variance from a full 200 bar charge to my refill level of 100 bar shooting 50 shots was 3fps. It was rated to do 210bar to 80 bar but the spread was greater.

Personally I think they should only test it with the pellets you have on you at the time you are stopped.

 

[penfold]

Accuracy isn't really the issue; if they don't have a piece of paper with a current test date on it(and an operator trained in the use of the apparatus) a decent lawyer will have you home in time for tea and medals. From a quick google the majority opinion is setting your gat up to produce ~11ftlbs is the safest bet for avoiding your collar getting felt. Up here in Scotland we have the joy of blanket FAC coverage soon; the fun police really went to town and have yet to grasp how ridiculous the whole thing is.

 

[Justme]

Yeh was the same with speed cams for a while till they got the paperwork sorted.

Whats the blanket FAC?

 

[penfold]

Yeh was the same with speed cams for a while till they got the paperwork sorted.

Whats the blanket FAC?

They're morons who think that a blanket FAC will a) attract votes(maybe, but the cost of administering it will grossly outweigh any measurable benefit) b) reduce airgun crime from the already minute level it's already at c) because TABLOIDS! Murdering gunslinging scum! etc. Basically a toddler was shot by a scumbag a decade or so ago, and the parents made a fuss and raised a petition, and now politicians 'must do something'. Inflicting blanket FACs on everyone with a plinking tool is the 'something'. This is what you get when there's a parliament filled with politicians without an actual country to run, just horning in on what councils ought to be doing.

 

[Thejoker123]

Is it advisable to de-frost a chicken before before it goes stratospheric ,Assuming it perhaps goes a little higher and upon re-entering the earths atmosphere would it be cooked enough ?so the question is. If one were to take a piece of 6inch salt glazed sewer pipe,charged with 80%methane and 20%pure oxygen at what time
Would one need to light the 'touch paper' in order for said chicken to return to earth via through the roof of intended dwelling to present itself for Sunday dinner.calcs for trajectory etc.