can someone explain power change by pellet weight ?

[mickmep]

just read the thread on hw loosing power and seeing the results using different weight pellets

reminded me of when i crono'd my rapid. was running legal power - just - with jsb's

and running about 12.7 ft-lb with bisley magnums.

before anyone jumps in i know it was illegal but i bought the gun secondhand like it and as

a responsible person have taken my spanner to it and its now running legal power

using bisley magnums.....................but my problem is below. :look:

 

i dont get this power changing by using different pellets.

cant get my head around why a pellet makes the gun have different power,

surely if the pellet weights more with the same air pressure pushing it it will go slower

therefore a lighter pellet will go faster than a heavier one which i can understand

but why is the power (ft-lbs) of the same gun changing if a lighter and heavier pellet is used ?

 

can someone please explain in laymans (simpletons) terms.

[scuta]

I'm with you on this one!!!

[Billy.]

Ft/LBS is calculated using the mass of the bullet, plus a number of other variables. This, in conjunction with the fact that different brands of pellet will be lubricated differently, will add/subtract to the Ft/LBS of energy that the pellet exerts.

 

I think you're thinking the GUN is 12.7 ft/lbs and not the pellet. This is the measurement of the force that the pellet is exerting at the muzzle of the airgun, not the energy the gun is producing to fire the pellet.

Edited March 20, 2010 by harfordwmj

[mickmep]

not plain english.................sorry

to me it seems that the lighter the pellet the lower the enegry (ft-lbs) if they are travelling at the same speed.

which does makes sence until the lighter pellet travels faster therefore having more travelling energy.

but it still doesn't explain why the same gun exerting the same pressure on the pellet

is giving different power readings.

[Paddy Galore!]

don't confuse muzzle energy with muzzle velocity, a lighter pellet will travel quicker because the air charge has less weight to move, the down side to this is it has less momentum and will cause less trauma. The slower, heavier pellet will carry more momentum or "energy". someone is bound to post the equation on here soon enough so you can work it out.

for example.. it's the difference between getting hit by barry mcguigan, and mike tyson..

[Billy.]

not plain english.................sorry

to me it seems that the lighter the pellet the lower the enegry (ft-lbs) if they are travelling at the same speed.

which does makes sence until the lighter pellet travels faster therefore having more travelling energy.

but it still doesn't explain why the same gun exerting the same pressure on the pellet

is giving different power readings.

 

There are endless variables that can alter the power of different brands of pellet fired from a gun. However a simple one is the lubricant.

 

If you use cheap pellets that are very dry, you'll find they have a much lower ft/lbs reading than those which are well oiled.

 

The shape of the pellet will alter the ft/lbs... The list is extensive.

 

Like I said before, the gun isn't 12 ft/lbs, the pellet is. A gun would probably be rated in Joules and the energy that the gun produces will be nowhere near 100% of an energy transfer to the pellet.

Edited March 20, 2010 by harfordwmj

[mickmep]

don't confuse muzzle energy with muzzle velocity, a lighter pellet will travel quicker because the air charge has less weight to move, the down side to this is it has less momentum and will cause less trauma. The slower, heavier pellet will carry more momentum or "energy". someone is bound to post the equation on here soon enough so you can work it out.

for example.. it's the difference between getting hit by barry mcguigan, and mike tyson..

 

i dont think i'm confusing the two things.

if i remember from school energy = mass x velocity (i really do hope this is correct)

 

if the gun is producing the same power each shot (joules) to propel the pellet

i still cant see how a heavier pellet which will be travelling slower will be more powerfull than a lighter pellet travelling faster.

surely the mass and velocity are just changing and the energy they started with is still the same.

if the energy they start with is the same how can the terminal energy be different ?

 

not convinced by the lubricating of the pellet, surely the pellet doesn't get better lubricated the heavier it it ?

for example using 2 different weight bisley pellets both the same shape.

 

not trying to be an a*se about it just dont quite see how it works.

 

anyways thanks for taking the time to reply.

[bruno22rf]

I would guess that efficiency is what we are looking at here-the gun puts the same amount of energy into each pellet so any variation in kinetic energy downrange must happen from the point of firing onwards.Take a look at velocity-the lighter pellet will travel faster than a heavy one and thus cause more friction and a greater loss of velocity than its heavier brother-add this to the fact that the lighter pellet is already carrying less energy because of its lower weight then the variations in pellet performance become clearer.The disadvantages of lower energy despite higher velocity become less important if the higher velocity has added benefits such as less drop over a given range.On the same lines the benefit of a higher energy carrying heavier pellet is lost if you cant hit a cows butt with it because of the arc of the trajectory.This is my theory and it helps me sleep at night-but then they do say that ignorance is bliss.

[Billy.]

not convinced by the lubricating of the pellet, surely the pellet doesn't get better lubricated the heavier it it ?

for example using 2 different weight bisley pellets both the same shape.

 

Ever tried punching underwater?

 

I think you've completely missed the point. It's nothing to do with the weight. It's to do with the efficiency of the pellet.

 

The better lubricated, the less energy it will lose through friction in the barrel.

Edited March 20, 2010 by harfordwmj

[mickmep]

Ever tried punching underwater?

 

I think you've completely missed the point. It's nothing to do with the weight. It's to do with the efficiency of the pellet.

 

The better lubricated, the less energy it will lose through friction in the barrel.

 

thanks for the replies hartfordwmj, but i think were both stuck in our ways of seeing it.

i do appreciate the replies and the effort it must be taking to get me to understand, i'm sure i am not alone in not understanding it.

i get the punching underwater v's air but your not firing one under water and one in air, they are both fired into the same air.

the only variable is the pellet weight.

same pellet shape, same pellet manufacturer, same lubrication.

and still the lighter pellet, propelled by the same gun will give a different (lower) ft-lbs.

 

i get bruno22rf point about downrange trajectory, but the ft-lb is measured directly the pellet leaves the barrel.

in the same place for a light or heavy pellet.

[Vipa]

Very simply.... You are assuming that keeping the air volume the same and varying the projectile weight would have a linear affect on muzzle energy, whereas in reality it doesn't, the graph is curved. You must realise that for any given weight of projectile the breech pressure will be different so don't get confused with volume of air vs pressure.

 

Think about it... (these are made up numbers to get my point accross) if you have a projectile that is for arguments sake 10 grains and you squirt 1 litre of air into the space behind it then a certain pressure will build before the projectile starts to move. If you increase the projectile weight to 20 grains then squirt the same 1 litre of air in, the pressure will be greater before the projectile begins to move, again varying the projectile weight whilst keeping all other factors constant would not produce a linear pressure graph, it is this that then causes the muzzle velocity & energy graphs to be non linear.

 

It's all about transfer of energy. When you pull the trigger a measured quantity of air is released into a chamber of constant size over a constant period of time. That charge of air is carrying a set amount of potential energy, that energy is transferred to the projectile and is then converted into kenetic energy... The question is, how much energy is transfered and converted and how does pellet weight play a part in the transfer. Surprisingly, you will find that the easier it is to get the pellet moving (i.e. the lighter pellet) the less energy is transferred. Remember this only applies to air weapons, firearms which work by burning propellant are a different kettle of fish.

 

Unlike a firearm where burning propellant in a controlled way causes a gradual increase in pressure as the bullet is pushed down the barrel, with an air weapon, the pressure peaks instantly and then it's all down hill so the more it takes to get the pellet moving the more enrgy is imparted into the pellet in the form of velocity. Once we have our initial 'push' the pressure behind the pellet is only falling, i.e. no more energy can be put into that pellet. So, a lighter pellet will start it's journey with a lower energy transfer than a larger pellet and will therefore contain less energy when it reaches the muzzle. As an example if you used our example of a 20 grain pellet, let's say it exits the barrel at 500fps, if you put the 10 grain pellet in it would not travel at 1000fps even though on the surface you would expect it to!

 

So, in conclusion, heavier pellets are more efficient than lighter pellets as more energy is transferred to the pellet when you pull the trigger.

 

Hope that helps.... I need another beer!!!

Edited March 20, 2010 by Vipa

[mickmep]

don't get confused with volume of air vs pressure.

this made sence when i first read it but.....................

would the volume of air not have the same energy to put into the pellet though.

there will be the same volume of air for each shot at the same pressure.

i get the heavier pellet takes more energy to start on its travels, and will be travelling slower.

but surely it gets back to my point that both pellets have had the same energy input at the start.

 

could it be that the heavier pellet takes more energy from the shot than the lighter pellet ?

if i reason it out the lighter pellet has departed the barrel using less energy to propel it down the barrel

and there is excess energy from the air pressure / volume which is not put into the pellet as its already left the barrel,

whereas the heavier pellet takes longer to start its travels and there is less excess energy when the pellt leaves the barrel.

 

not sure if i've explained that very well but basically not all the energy from the air charge is transferred to the pellet, some is blown out the end of the gun.

[SSS]

Imagine it like a double decker bus (heavier pellet), compared to a car (lighter pellet). The bus will take more energy to get it going, hence lower MV, but once it gets going it takes more to stop it, carrying more energy with it as it goes, hence higher ME.

 

Does this confuse things more?

 

(I havn't read most of the above posts, so excuse me if it has already been answered, its late, and I'm tired (old age setting in I think))

 

All the very best,

SSS

Edited March 20, 2010 by SSS

[Billy.]

I get what you're saying, but as above, you're assuming that everything is running on a linear graph.

 

If you kick a football with 50% of your total ability and it travels at 40 mph, you will not get the ball to travel at 80 mph if you kick with 100% as the factoring is not doubled. I think it's quadrupled, but I am currently searching the internet for the exact law on this.

 

What you've said here:

 

"not sure if i've explained that very well but basically not all the energy from the air charge is transferred to the pellet, some is blown out the end of the gun."

 

Is true, but there are literally hundreds, if not thousands of other variables which also constitute a loss of energy. Even the fact that you're using two pellets from the same manufacturer, but in different tins. They'll be different batches, might be slightly older so the oils will have evaporated, dented, has a bubble in the lead, scratched... The list goes on and on and that's just the pellet.

[Vipa]

this made sence when i first read it but.....................

would the volume of air not have the same energy to put into the pellet though.

there will be the same volume of air for each shot at the same pressure.

i get the heavier pellet takes more energy to start on its travels, and will be travelling slower.

but surely it gets back to my point that both pellets have had the same energy input at the start.

 

could it be that the heavier pellet takes more energy from the shot than the lighter pellet ?

if i reason it out the lighter pellet has departed the barrel using less energy to propel it down the barrel

and there is excess energy from the air pressure / volume which is not put into the pellet as its already left the barrel,

whereas the heavier pellet takes longer to start its travels and there is less excess energy when the pellt leaves the barrel.

 

not sure if i've explained that very well but basically not all the energy from the air charge is transferred to the pellet, some is blown out the end of the gun.

 

Have another read of my post, I think I've edited to make a little more sense and actually comes to the same conclusion that you have.

[mickmep]

Have another read of my post, I think I've edited to make a little more sense and actually comes to the same conclusion that you have.

 

yes i think i am thinking of it the same way now.

my problem to start with was thinking the same energy was put into the pellet.

reasoning it out that the lighter pellet needs less energy to get itself moving makes sence.

and the fact that not all the energy the gun produces gets transfered to the pellet.

 

thanks for the replies..................i slept well last night

 

hartfordwmj............still dont get the lubrication bit they've all got pellet lube on them

and none of my pellets are bent or scratched either i've a strick quality control regime

seriously though thanks for the replies, i think i've got there

[Billy.]

hartfordwmj............still dont get the lubrication bit they've all got pellet lube on them

and none of my pellets are bent or scratched either i've a strick quality control regime

seriously though thanks for the replies, i think i've got there

 

uurrrgghhhh!! I literally give up! You are looking at things on a large scale and not factoring in the microscopic variables that change the resistance that's caused between the pellet and the barrel. If you take your perfectly formed pellets and look at them under a microscope, you'll see the surface is far from flat, which means each pellet will seat differently in the barrel, meaning some air may get past, or one area might rub more than the other. This, along with the fact that no single pellet will have the exact same lubrication as the last, will affect the flight/speed/accuracy of the pellet.

 

I can assure you that there will be a big difference in variables between two tins of pellets from the same manufacturer. What you think is that they're identical to the eye and that's all that counts.

Edited March 21, 2010 by harfordwmj

[Paddy Galore!]

This is getting painful... It's a beautiful day out there, relax, take a chill pill, and can someone please post the equation that calculates the ft/lbs wotsit?

[mickmep]

uurrrgghhhh!! I literally give up! You are looking at things on a large scale and not factoring in the microscopic variables that change the resistance that's caused between the pellet and the barrel. If you take your perfectly formed pellets and look at them under a microscope, you'll see the surface is far from flat, which means each pellet will seat differently in the barrel, meaning some air may get past, or one area might rub more than the other. This, along with the fact that no single pellet will have the exact same lubrication as the last, will affect the flight/speed/accuracy of the pellet.

 

I can assure you that there will be a big difference in variables between two tins of pellets from the same manufacturer. What you think is that they're identical to the eye and that's all that counts.

 

cheers.

please dont give up on me.

i do understand what you are saying, which is why with an airgun the ft-lbs varies from 1 shot to the next,

using the pellets from the same tin. the microscopic variable as you say.

it just seemed that using 2 completely different brands of pellet, say bisley magnum and jsb exacts,

the main difference was the pellet weight, not the lubricant. and the lighter pellet always had less power ft-lbs.

 

many thanks for taking the time to reply.

 

regards mick.

[SSS]

Lighter pellet has a lower ME and a higher MV because it is easier for the gun to 'push' it out of the barrel.

 

The heavier pellet has higher energy because it takes more force to get it going, hence more force once it is going.

 

Billy, you are looking at it in too much detail IMO, it makes perfect sense in what you are saying, but all he was asking is why there is a difference in ME and MV between lighter and heavier pellets.

 

All the best,

Sam

[SSS]

I have thought of another way to explain this, and it has woken me up thinking about it, so best get it out whilst I remember.

 

Imagine your lighter pellet is a small pebble, the sort you put on your drive to make it look nice.

 

Now imagine the heavier pellet is a breeze block, the sort of things that are used in construction.

 

Imagine somebody throwing said pebble and breeze block at your head, it will take a lot more effort to throw the block compared to the pebble, and the flight of the pebble will be much faster, but, and it is a rather big but, when the two said projectiles (pebble and breee block) become terminal, and hit you in the head, the heavier object will transfer more energy, and cause more damage.

 

Please tell me this makes complete sense and I really hope this helps.

 

As for now, I'm going to get some more kip.

 

All the best,

SSS

Edited March 24, 2010 by SSS

[Paul223]

Very simply.... You are assuming that keeping the air volume the same and varying the projectile weight would have a linear affect on muzzle energy, whereas in reality it doesn't, the graph is curved. You must realise that for any given weight of projectile the breech pressure will be different so don't get confused with volume of air vs pressure.

 

Think about it... (these are made up numbers to get my point accross) if you have a projectile that is for arguments sake 10 grains and you squirt 1 litre of air into the space behind it then a certain pressure will build before the projectile starts to move. If you increase the projectile weight to 20 grains then squirt the same 1 litre of air in, the pressure will be greater before the projectile begins to move, again varying the projectile weight whilst keeping all other factors constant would not produce a linear pressure graph, it is this that then causes the muzzle velocity & energy graphs to be non linear.

 

It's all about transfer of energy. When you pull the trigger a measured quantity of air is released into a chamber of constant size over a constant period of time. That charge of air is carrying a set amount of potential energy, that energy is transferred to the projectile and is then converted into kenetic energy... The question is, how much energy is transfered and converted and how does pellet weight play a part in the transfer. Surprisingly, you will find that the easier it is to get the pellet moving (i.e. the lighter pellet) the less energy is transferred. Remember this only applies to air weapons, firearms which work by burning propellant are a different kettle of fish.

 

Unlike a firearm where burning propellant in a controlled way causes a gradual increase in pressure as the bullet is pushed down the barrel, with an air weapon, the pressure peaks instantly and then it's all down hill so the more it takes to get the pellet moving the more enrgy is imparted into the pellet in the form of velocity. Once we have our initial 'push' the pressure behind the pellet is only falling, i.e. no more energy can be put into that pellet. So, a lighter pellet will start it's journey with a lower energy transfer than a larger pellet and will therefore contain less energy when it reaches the muzzle. As an example if you used our example of a 20 grain pellet, let's say it exits the barrel at 500fps, if you put the 10 grain pellet in it would not travel at 1000fps even though on the surface you would expect it to!

 

So, in conclusion, heavier pellets are more efficient than lighter pellets as more energy is transferred to the pellet when you pull the trigger.

 

Hope that helps.... I need another beer!!!

To add to that, as the trigger is pulled the air pressure builds behind the pellet, it may seem like a instant but that is not the case, a spring powered gun will build up enough pressure before the piston hits home and both spring powered and pcp must transfer the air through a port, again for round figures lets say the 10 grain pellet starts to move at 50 psi as it starts to travel down the barrel the space behind it gets bigger, air is still flooding through the port and into the expanding space behind the pellet constantly raising the pressure, the pellet is now 10 inches down the barrel travelling at a speed of 600fps but not much slower that the expanding air behind it, therefore no longer gaining much more momentum and no longer absorbing (lots of) energy and exiting the barrel at 625fps, the 20 grain pellet requires much more energy to start moving, lets say 80psi, the space behind it expands in the same way but at a slower pace because the pellet is moving more slowly due to it heavier mass, therefore the pressure builds higher, at 10 inches the pellet is travelling at 450fps the slightly slower pellet is still travelling slower than the built up ( and still building) pressure can push so it is still gaining momentum, and therefore still soaking up more energy as more of the air charge has acted on it, exiting the barrel at 525fps, hope this helps, bit early for a beer though i'll have a coffe instead

[mickmep]

cheers SSS

i've been sleeping ok since i realised the difference was not all the power of the gun was imparted to the pellet.

maybe its answered the question for a few more people as well, i'd like to think i'm not the only one who didn't understand it...................

 

i even asked the misses, who knows everything , and she didn't know

[Vipa]

This is getting painful... It's a beautiful day out there, relax, take a chill pill, and can someone please post the equation that calculates the ft/lbs wotsit?

 

Muzzle energy is calculated by the formula E=MV2/450400 for the imperial system and E=MV2/2000 for the metric system.

M is bullet mass in grains or grams (depending on the UOM, 0 < M < 2000.00 grains or 130 grama)

V is the bullet velocity in ft/sec ( 0 < V < 5000.00 fp/sec or 1500 m/sec)

The constant 450400 comes from 7000 ( grains in a pound ) multiplied by (g=32.17) by 2.

2000 comes from 1000 ( grams in kg ) multiplied by 2

Only first two decimal digits are used.

 

But you already knew this!!!

[Dekers]

Muzzle energy is calculated by the formula E=MV2/450400 for the imperial system and E=MV2/2000 for the metric system.

M is bullet mass in grains or grams (depending on the UOM, 0 < M < 2000.00 grains or 130 grama)

V is the bullet velocity in ft/sec ( 0 < V < 5000.00 fp/sec or 1500 m/sec)

The constant 450400 comes from 7000 ( grains in a pound ) multiplied by (g=32.17) by 2.

2000 comes from 1000 ( grams in kg ) multiplied by 2

Only first two decimal digits are used.

 

But you already knew this!!!

 

 

...and in theory, if you check the pellet weights, and have an accurate chrono, this will take into account pellet variations of quality/lube/raw materials, etc, so all else goes out the window and you will get an accurate result.

 

Bottom line is, all being equal a heavier pellet carries it's energy more efficiently than a light one. The all being equal bit being very important.

 

ATB!!