Mathmatics / Photography Question (Semi-Urgent)

Is there any way to calculate how much a bullet will move a stationary target upon impact, or the speed at which the target will move?

I have a piece of bullet-proof polycarbonate, an AK-47 and a $600 Canon DSLR. My plan is to put the camera behind the poly, and fire at it.

I'll guess that the polycarbonate weighs 4 pound, and the projectile will weigh about 8 grams and travel at 2,400 feet per second.

I just don't know if I should have my camera right against the polycarbonate or not. It will stop the projectile, no question. But I don't want it to stop the thing and shatter the lens from the energy it absorbs.

To clarify, I won't be intentionally firing at the camera, just close enough to get a neat picture. The polycarbonate is kind of the last line of defense, in case something goes wrong.

 

I think you need to be part of the Mythbuster team or their friend "Frank" (retired FBI) to be able to guesstimate that but it seems to me that they always do at least one trial of that anyway. Do you by chance have 2 pieces of polycarbonate? Put a wine glass against it and see if it survives.

You aren't going to clamp the polycarbonite? I would think some sort of bracing and clamping would be your best defense and most reasonable option. Going to be faster to build a frame and brace and bolt it down than it is going to be to guess and hope about how much the your target is going to move.

 

I agree, bracing with a clamp makes the most sense, but I'm working with what I have on hand. I'm sure that the bullet isn't going to stop instantly. I plan on bracing as well as I can, maybe with cement blocks, or something like that. I think that'd be enough to transfer the poly to a forward motion. I suppose I'll know in an hour, if it works, I'll post a pic or two. If not, I'll post a pic of my new camera! LOL

I hope it works, haha. Thanks for the Mythbusters reference! Love it.

 

Any of this help?
http://en.allexperts.com/q/Physics-1358/2011/3/kinematics-problem-solving.htm

 

If I may..
7.62 x 51 mm Std. Nato 150 gr. FMJ MV 2,800 fps. At the muzzle 2,580 + foot pounds of energy
I'm sure someone on here can do the math.... but its gonna hit HARD.. lol
First law of physics huh... for every action...
You better clamp it... tight...
Good luck:-D

 

LOL, move the camera back. Install a rubber lens ring. don't stand behind the camera when you shoot.

How are you going to time that shot?

 

fire one shot without the camera, then measure the movement
then you will know where to place the camera safely

 

Bit late, but I'm with StanW on this . . .

I would fire three test shots from a stable platform, measure the movement each time and take the average of the three tests. That would give you pretty reliable data to operate with. Assuming you have the material to use for the tests, that is . . .

I hate math . . . plus test shots are fun :-D

 

The formula for impact energy is Bullet Weight x Velocity^2 / 450,437.

Or to put it in words it is the weight (in grains) times the square of the bullet velocity (in feet per minute) divided by 450,437.


this is an energy calculator that may help.

http://www.handloads.com/calc/quick.asp

EDIT
I forgot to say that it is the velocity at impact so you need to use the chart on you cartridge box to see the velocity at the distance you will be shooting.

 

No one puts cameras in front of bullets in the film word,even if the polycarbonate doesn't move a chunk or to use the technical term 'scab':-D could fly off the back and brake the camera anyway.

What movie makers do is put a mirror behind the polycarbonate,angle the mirror at 45 degree's then place the camera off to one side.

IMO the energy equations won't help much because most of the energy will be used deforming the round and flexing/braking the polycarbonate,a good way to see how much the polycarbonate could possibly move would be to hold the stock of your AK to the polycarbonate then fire a round down range letting the polycarbonate absorb the recoil, this will give you maximum the poly can move backwards even if it absorbed 100% of the bullets energy, if you would like peace of mind.

Little diagram,while its Sunday:-D The mirror also usually get destroyed.

 

you are perfectly correct Rikky, the only way to get a true reading is to use instruments on the polycarb itself.
There are many variables that will cause the values to change, barrel length is one, the equation i gave is for the standard 20 inch barrel but for each inch shorter than that the muzzle velocity will drop 80 feet per second, distance and air temp/humidity are also factors.

What i did was give the basic maths formula to give a general idea.

 

I wasn't disputing Bill,just giving an opinion and alternative method EDIT TBH I didn't even read math and I'm not doing now on Sunday,letting my BLT digest

 

Thanks for all the responses everyone. Tim, I wanted to get a picture head on of the muzzle flash from the gun. I thought that maybe the bullet would form some kind of eclipse within it, but mostly just to have the picture, as I'm sure it's rather rare.

Anyway, I did end up firing a test shot, and because my two weapons where my 9mm carbine, and my ak-47 I used the heavier of the two for the shot. I'll add some pictures of everything, but you can see that the polycarbonate didn't have any trouble stopping the 9mm (on one occasion, it didn't even achieve full penetration, and was hanging out of the stuff! But, the AK-47 zipped right on through, which wouldn't have went so well for my camera, LOL.

I set the camera up on a tripod beside me though, and ended up with a picture that I'm somewhat happy with. I don't think I could do any better without a person firing the camera, really.

 

Looks like fun Pax! Don't know if you have seen this, but has some good video of AR's and AK's being shot.

http://www.youtube.com/watch?v=G6BpI3xD6h0

 

Paxton that looks like fun!