How hard is my air soft shotgun hitting?

How hard is my air soft shotgun hitting? - Printable Version

+- Southperry.net (https://www.southperry.net)
+-- Forum: Social (https://www.southperry.net/forumdisplay.php?fid=14)
+--- Forum: Rubik's Cube (https://www.southperry.net/forumdisplay.php?fid=58)
+--- Thread: How hard is my air soft shotgun hitting? (/showthread.php?tid=11325)

How hard is my air soft shotgun hitting? - IllegallySane - 2009-05-15

Thought some bored physics people may want to wrap their heads around this.

It's an air soft shotgun that I bought because it looked cool, and would be better than using pistols that I have to cock back for each shot, while the shotgun is an easier pump action.

I have no idea how strong my shotgun really is, because I use my pistols in mock firefights with my friends, who have better arms than me, like an M4 electric air soft rifle, and an electric P90. I wanted the shotgun so we'd have a more even fight. We wear goggles when we fight, because while we shoot each other for fun, we know better to get shot in our arms or legs multiple times than to risk losing an eye. We also don't directly shoot each other because we hide behind furniture and we fire with about 10-15 feet of distance between each other, or more.

Here's the conditions. The shotgun is about the size of the one Arnold holds in Terminator 2:

Spoiler

The only minor differences is I pump it from below the barrel to reload instead of having it near the trigger. It also doesn't look as nice since he's all black plastic and has the orange tip at the barrel to let people know it's not a lethal weapon. Rolleyes

It fires at 300 FPS, or 300 feet per second.

The plastic BB's that I use are 6mm, 0.12 grams.

I loaded the pellets and fired at a small plastic container like this 0.28 L container:
[Image: Plastic_Container.jpg]

The plastic was not soft, but rather hard like those Hinckley Springs Water plastic.

From a 5 feet distance, 2 feet high, pointed down about 30 degrees (that means the barrel itself is actually the square root of 29 feet, or 5.385 feet from the container) I fired at the upside down container out of sheer boredom. After firing, I was shocked. The BB went through both sides of the container, leaving pretty impressive holes. They were not pierced clean like a needle, but shattered because the BB took a small piece of plastic with it when it went through. I made several more shots at the same distance. They all made cracked holes in the container, like this:

Spoiler

For a comparison, I used my pistol and shot the same container, at a 2 feet distance. It made a cracked hole only through the first side. The BB merely bounced inside the container afterward.

Yay for abstract physics? Poast

So considering a shotgun with 6mm, 0.12 gram pellets shot from a 5 feet distance pointed down 30 degrees traveling at 300 FPS and shattered both sides of a #5 plastic container, what are:

1. The force it was hitting?
2. How painful would it be on a person from the same distance?
3. Is it painful enough that I should forbid myself from using it in a mock firefight?

There's no need to get super exact, I just want to know a rough estimate of the force it's traveling at.

How hard is my air soft shotgun hitting? - Fiel - 2009-05-16

Interesting. I think it'd be interesting had you filled the containers with water and then fired at them. I bet they wouldn't go through then. Wink

How hard is my air soft shotgun hitting? - IllegallySane - 2009-05-16

Fiel Wrote:Interesting. I think it'd be interesting had you filled the containers with water and then fired at them. I bet they wouldn't go through then.

I'll take your challenge, and do it at an open area sometime tomorrow. Wink

How hard is my air soft shotgun hitting? - Tempus - 2009-05-16

Assuming your shotgun is the same size as a Winchester 1887:

$[Image: eq.latex?\begin%7Balign%7Da&=\frac%7Bv%5E2%7D%7B2s%7D\...end%7Balign%7D]$

$[Image: eq.latex?\begin%7Balign%7DF&=ma\\&=0.00012\t...end%7Balign%7D]$

So it's hitting with a force of about 1N.

What might be more useful is the stress:

$[Image: eq.latex?\begin%7Balign%7D\sigma&=\frac%7BF%7D%7BA...end%7Balign%7D]$
The stress is only rough because the area of the BB that hits is alot smaller than the area I used here (just taking it's diameter). I'm not sure how much stress hurts, but I've seen somewhere that 20 psi (= 6894.757 Pa) bruises the skin.

But I could be totally wrong. Tongue

How hard is my air soft shotgun hitting? - IllegallySane - 2009-05-16

Tempus Wrote:Assuming your shotgun is the same size as a Winchester 1887:

$[Image: eq.latex?\begin%7Balign%7Da&=\frac%7Bv%5E2%7D%7B2s%7D\...end%7Balign%7D]$

$[Image: eq.latex?\begin%7Balign%7DF&=ma\\&=0.00012\t...end%7Balign%7D]$

So it's hitting with a force of about 1N.

What might be more useful is the stress:

$[Image: eq.latex?\begin%7Balign%7D\sigma&=\frac%7BF%7D%7BA...end%7Balign%7D]$
The stress is only rough because the area of the BB that hits is alot smaller than the area I used here (just taking it's diameter). I'm not sure how much stress hurts, but I've seen somewhere that 20 psi (= 6894.757 Pa) bruises the skin.

But I could be totally wrong.

It's only ~1/20 the strength to bruise skin? It sounds very reassuring then since it would imply it can't bruise the skin when if shot at point blank range. However, how would that explain it being able to shatter the #5 plastic container through both sides? To me, it looks like it's way more than 1 newton of force, or I could be wrong and totally underestimated the plastic container that I used. :f6:

How hard is my air soft shotgun hitting? - Tempus - 2009-05-16

Well it's only 1 N of force but because it's applied over a small area, it does more. Like I said, my answer is an underestimate because I took the area based upon the diameter (which is the largest of the BB's cross-sectional areas) and as the area gets smaller and smaller, the force per unit area gets closer and closer to infinity.

How hard is my air soft shotgun hitting? - XTOTHEL - 2009-05-16

I don't think F = ma applies here. Calculating F = ma only gives the amount of force applied to the pallet.

I think this can be solved with Momentum (p = mv), Impulse force (m * delta(v)) and maybe even kinetic energy (E = 1/2mv^2)

How hard is my air soft shotgun hitting? - Tempus - 2009-05-16

And wouldn't the BB hit with the same (if not less) force?

Also, I don't think he knows the velocity he's recoiling at, so equating the fact that the two momenta must be equal is going to be hard. And I tried it using kinetic energy, you still get 1N.

How hard is my air soft shotgun hitting? - JoeTang - 2009-05-16

Tempus Wrote:Well it's only 1 N of force but because it's applied over a small area, it does more. Like I said, my answer is an underestimate because I took the area based upon the diameter (which is the largest of the BB's cross-sectional areas) and as the area gets smaller and smaller, the force per unit area gets closer and closer to infinity.

The force applied is independent of the area it is applied over.

Your equation isn't considering drag. Also, your acceleration assumption is wrong. I don't think it's possible to determine acceleration because the force applied is based on the acceleration change between the moment it impacts the skin and the moment its velocity is zero, not the moment between the time it exits the barrel and then stops.

How hard is my air soft shotgun hitting? - Tempus - 2009-05-17

JoeTang Wrote:The force applied is independent of the area it is applied over.

The force is independent yes, I don't ever remember saying it wasn't. I said the effect of a force depends upon the area it's applied over.

JoeTang Wrote:Your equation isn't considering drag. Also, your acceleration assumption is wrong. I don't think it's possible to determine acceleration because the force applied is based on the acceleration change between the moment it impacts the skin and the moment its velocity is zero, not the moment between the time it exits the barrel and then stops.

Considering drag is complicating things beyond the "rough estimate" that was asked for. And yes, my assumption is wrong, but there's not much else to go on. You're more than welcome to post your own answer to the question. Smile

How hard is my air soft shotgun hitting? - XTOTHEL - 2009-05-17

((0.00012 kg) x (91.44 (m / s))) / (0.001 s) = 10.9728 newtons

This is assuming the time of impact is 1milisecond, could be less.

How hard is my air soft shotgun hitting? - Tempus - 2009-05-20

XTOTHEL Wrote:((0.00012 kg) x (91.44 (m / s))) / (0.001 s) = 10.9728 newtons

This is assuming the time of impact is 1milisecond, could be less.

And the impact time could be more. Tongue

I'm not sure what the average impact time of a BB is, but it being 0.01s (possible?) would give you 1N.

Knowing more about the situation it could be calculated correctly but they're all based upon assumptions so far.