How Much ENERGY is actually delivered to a target struck ? ... A Conversation

[Motorhead]

Over in the FT area some talks about slugs being used / Now banned for the FT game some of this conversation needed IMO it's own post for conversation.

Origins of this post is here: Slugs in FT





SO, let start this my sharing my own physics logic and see what sticks or does not , Lol



Lets just start this stating an even number & we are going to use 20 FPE. Term Projectile is that of a Pellet or Slug ( Tho may be defined in a point being made )

Now this figure is a calculated number based upon a projectiles WEIGHT and SPEED measured at muzzle. I am going to assume that this 20 FPE is arrived at if said projectile was stopped DEAD IN IT TRAVEL against a surface if would transfer 20 fpe to that surface ? Lets relate to a sand bag dropped a few feet. THUD & Stopped !



If and when a projectile is unable to contain its mass by blowing apart, splattering etc .... it has not stopped dead even tho destroyed. Much of its potential energy has been dissipated by the fact its mass ruptured in many directions. I DON'T THINK our 20 FPE was delivered to the struck surface in this situation. 

For the lead projectile in this case, for it to rupture it mass, coming apart takes energy to do so. This energy came from the 20 fpe "Potential" leaving something less to be transferred onto the struck surface.



Thus my thoughts on the Pellet to Slug debate on which does more target damage ? A more fragile pellet that more times that not completely Grenades into a lead dust cloud has used a lot of energy up. More it comes apart and deflects 90* to struck surface, less mass it possesses and retained energy going towards the struck surface.

* Now in FT for most in the game they know I'm keen on .20 cal for this sport. Those who I shoot with mostly shoot .177 and there pellets go to dust upon impact, where as my .20 most times leaves behind a Lead Pimple stuck there. Who's Pellet you think is putting the most energy into the struck surface ?



 Slugs IMO behave very similar in that a lot of a slugs mass remains intact upon impact having the struck surface absorbing more energy. If the slugs mass / lead is not turned 90* and sent outward away from contact, it kept going forward placing MORE RETAINED FPE into the struck surface.



Ok, There is a start to what I hope is a constructive conversation

Scott S

 

[ScottEnglish]

Seems easy enough to set a chrono at FT targets at all distances to determine energy of pellets/slugs hitting the kill zone or face plate.

 

[dizzums]

i think you got it .. 'small' pellets generally splatter on impacting a hard surface .. larger caliber pellets or slugs retain more mass going forward and penetrate more .. im sure exotic materials could be used like teflon coated depleted uranium .177 pellets that would drill holes in those ft targets lol .. theyd prolly figure you out after awhile though lol ..

 

[Motorhead]

Hitting is one thing ... Transferring it to the strike paddle another !!!

It is not that simple as most assume it to be. We're not talking about catching a baseball intact here, only pieces of it that make if you will the catcher mitt feels the impact a whole lot less so.

Scott S

 

[Franklink]

Seems to me we're trying to make the square peg that is fpe, fit into a round hole. 

Only two factors go into foot pounds of energy: weight of the projectile, and the speed at which it is moving.

And there are two speeds of importance here. The muzzle velocity, which is how we determine a gun/pellet combination is field target legal, and the speed at which the projectile is moving when it hits the target (initial energy versus retained energy). Some might try to argue that the slug will have more retained energy (be moving faster than the pellet) when it hits because it has a higher BC but even that is minimal when we're talking about the sub 20fpe class and distances from 10-55 yards.

Some examples from Chairgun.....

Using the .20/13.72 grain pellet versus the .177/12.5grain slug. 

A 13.7grain pellet going at 800fps muzzle speed has 19.5fpe to start.

With a BC of 0.04 and using the GA drag profile it has 13.8fpe at 55 yards and 18.2fpe at 10 yards. 

A 12.5grain slug going at 838fps muzzle speed has 19.5fpe to start.

With a BC of 0.072 and using the G1 drag profile it has 15.9fpe at 55 yards and 18.7fpe at 10 yards. 

BUT a 12.5 grain slug going only 838fps will not have a BC as high as NSAs advertised 0.072. Much more realistically, it will have a BC more like 0.05 at the starting speed of 838.

With the realistic BC of 0.05 and starting speed of 838, it will have 14.5fpe at 55 yards (0.7fpe more than the pellet) and 18.4fpe at 10 yards (0.2 more fpe more the pellet). Those minimal differences are simply not going to result in significantly more target damage. 

While heavy .177 slugs are available with quite high BCs......(for the original purpose of this argument) I can't fathom anyone thinking that a 20.5 grain NSA slug going 660 (just under 20fpe) would be in any way competitive in field target. Additionally, those really heavy .177 slugs that are capable of high BCs are not going to have those high BCs when starting out so slow. So, the 'slugs have a higher BC" argument is out, in the context of keeping it field target legal.

 

[nervoustrig]

Bits of lead spatter flying off the target are carrying away a portion of the projectile's terminal energy. I can't see how there would be any doubt about it. These bits have mass and some particular velocity, thus if you could add them all up, you could quantify how much energy was wasted, so to speak, versus how much was actually dissipated in the target.

 

[Franklink]

Bits of lead spatter flying off the target are carrying away a portion of the projectile's terminal energy. I can't see how there would be any doubt about it. These bits have mass and some particular velocity, thus if you could add them all up, you could quantify how much energy was wasted, so to speak, versus how much was actually dissipated in the target.

Those bits of lead had to impact something hard enough to become bits of lead. A pellet doesn't just become bits of lead right in front of the paddle before imparting energy upon it, simply because it's a pellet and not a slug. 

 

[Motorhead]

Guys ... lets reel this back in and DISMISS what we are NOT talking about.

Not talking about how FPE figures get calculated ...

Not talking about degrading energy over distance ...

Not talking about BC or sectional density ...



We are wanting to converse about ...

The physics of transferred energy from one part in motion coming to an abrupt stop upon another object.

Having ... SADLY the part in motion coming apart shedding its mass/ weight while in motion against the other and how the physics of the energy transfer gets reduced as a result.



Do we really ever think about this ?

or just accept your right in thinking what ever retained energy a projectile has at any given distance is what the hit target actually absorbs ? 



I don't think that is correct ?

 

[Franklink]

Okay Scott, I see the direction you're wanting to take with the discussion, although "energy" may not be the correct word, cuz if it's energy, we're right back at foot pounds.

Maybe force? or net effect? I think you're wanting to somehow explore how those foot pounds are transferred to the target, and if it's different for a pellet or a slug. 

Newton:

• First Rule: An object will remain at rest or in a uniform state of motion unless that state is changed by an external force. 
• Second Rule: Force is equal to the change in momentum (mass times velocity) over time. In other words, the rate of change is directly proportional to the amount of force applied. 
• Third Rule: For every action in nature there is an equal and opposite reaction. 

All three apply in some way or another, but for the theory that fragmenting pellets don't impart as much force on a target I think the third rule is most applicable. In order for the pellet to fragment, it has to be imparting it's energy upon the paddle. Those pellets aren't flowing around the paddle, they are HITTING the paddle and the continued kinetic force of the pellet is driving the main mass of the pellet forward as the leading edges of the pellet are deflecting in 360 degrees away from the impact point as they shear away. ALL of that description involves the pellet imparting energy into the target though (coincidentally, however many fpe it had when it hit).

 

[Franklink]

I've been trying to devise a scientific way to measure what you're trying to illustrate. And keep arriving at one of two types of targets. Either a sled that moves away from the shooter and the distance it moved could then be measured after being shot with a 20fpe pellet compared to how much it moves when being shot with a 20fpe slug. Or a pendulum type target, not too much different than the swinging paddles that we shoot. The paddle would need to be heavy though, to prevent full or multiple revolutions, and a guy would need some hi speed cameras to analyze the difference in how far back and up the paddles are swinging after being hit with each of the projectiles in question.

 

[Motorhead]

In my thinking RULE 2 is where were at. 

The projectiles MASS is rapidly diminishing as is its Velocity More so with a pellet than a slug, thus there exerted force onto contact surface would differ in my mind ?



Yes, some sort of Newtons Cradle with a flat and somewhat heavy strike plate. How far the end ball of the cradle swings should show for a comparisons sake which put the most energy into the strike paddle.



Interesting conversation I never really read anything about ? We're not in firearms territory here and there typical FPE / Wound damage hydro-static shock type talks.

 

[nervoustrig]

Let's assume at the instant the projectile reaches the target, it is carrying 20 foot*pounds of energy. It shatters into 4 equal parts weighing 2gr, each of them departing at a velocity of 500fps. Each of these four pieces has ~1fpe for a total of 4fpe. The target absorbed the rest, 16fpe. 

 

[Franklink]

Let's assume at the instant the projectile reaches the target, it is carrying 20 foot*pounds of energy. It shatters into 4 equal parts weighing 2gr, each of them departing at a velocity of 500fps. Each of these four pieces has ~1fpe for a total of 4fpe. The target absorbed the rest, 16fpe.

Does the target absorb zero energy from the initial impact? For the pellet to break apart/fragment, I would think there has to be a release/transfer of energy, or "an equal and opposite reaction." (well, perhaps not "equal" but hopefully you get what I'm trying to say) 

 

[Solo1]

haven’t read all the replys yet but let me start by calling bull on pellets going to dust. i’ve personally been hit by aprox 1/2 of a pellet 3 times after it bounced off a 10 yd target but ive never been hit by any part of a slug and i shoot a lot indoors into a steel trap @ 11 m. in this conversation i think its necessary to consider target and paddle condition. is the paddle reinforced? is the paddle leaning farther than necessary? is the face misshapen? and as far as pellet and slug differences are concerned i think the differences are so small as to not really matter @ 20fpe. as far as im concerned the only real difference is the bc and how much each are affected by wind

 

[nervoustrig]

Does the target absorb zero energy from the initial impact?

There is a very short but finite interval of time over which the 16fpe is absorbed by the target. In other words, not 0.000 picoseconds and not 1 second. I am visualizing it as though we are watching it in super slow motion. During this short time, the projectile is deforming and disintegrating, and the paddle is beginning to move away, etc.

 

[nervoustrig]

haven’t read all the replys yet but let me start by calling bull on pellets going to dust.

Not dust per se, but small slivers that leave at high velocity. Granted, seen through a scope in brightly lit conditions against a dark background, it gives the appearance of a dust cloud. The larger bits have enough velocity to embed into the wood frame beneath a spinner target in my back yard:

 

[Motorhead]

All of the above ... Dust, fragments, particles large and small.

On club targets the back side of face plates turn Grey from finer lead dust, Pivot areas build up with what looks like molten slag and block they sit on pile up similar slag heaps.

Statement of Dust was incorrect by literal definition. So lets state such as obliteration of the pellet.

Our clubs FT target Strike paddles dent, then into BIG dents, then into holes eventually if not maintained.

 

[Franklink]

No disagreement from me on the destruction of a pellet from hitting a solid object. I've see it with field targets and other junk that I've shot. 

Let's look at this a different way though. Say the pellet is just sitting there, in its little waisted shape. In order for that dude to fragment, there has to be some force exerted upon it, or exchanged with it. So, let's say a hammer. In order to get that pellet to change shape (or even more drastically, to fragment) you're gonna have to smack it with that hammer pretty hard, there's an exchange of energy there, even if some of the fragments attain escape velocity and the net equation showing what energy went where would indeed account for the energy it took to send each fragment flying, energy had to be released/expended/expelled/transferred to start the whole process. Otherwise, the pellet is still sitting there in its little waisted shape. 

That energy is the 20fpe (or whatever percentage of that is left at X distance from the muzzle) being released. 

 

[L.Leon]

Let's assume at the instant the projectile reaches the target, it is carrying 20 foot*pounds of energy. It shatters into 4 equal parts weighing 2gr, each of them departing at a velocity of 500fps. Each of these four pieces has ~1fpe for a total of 4fpe. The target absorbed the rest, 16fpe.

I think the target absorbs the full 20 FPE at impact. The pieces that sheared off? Continue until they shed their energy?

 

[nervoustrig]

I think the target absorbs the full 20 FPE at impact. The pieces that sheared off? Continue until they shed their energy?

Conservation of energy...if the pellet arrived with 20fpe, and fragments of it left with 4fpe of residual energy, that 4fpe had to come from somewhere. So the question becomes, did the target receive all 20fpe and then give 4fpe of it back to the fragments...or are the fragments still carrying a portion of the original energy?