Home made body armor, amazing

[BigK]

Watching those guys test body armor made me think of Bill Engvall....here's your sign

[Peace]

Still doesn't explain how a 250lb man can move a 2500lb car. Or why a barret doesn't break the shooter's shoulder. 2000-3000 ft/lb of energy into your shoulder without breaking?  I think path of least resistance has a little to do with it. The energy is mostly directed out the barrel because it offers the least resistance so most of the enrgy is transferred to the bullet. What about this. If your AR had a buttstck the size of a .22 cal bullet, would it do the same damage to your shoulder to shoot it as it would to be shot by it? This is very interesting stuff.

 

Agreed. Lbs/sq inch.   that and... if you were leaning forward, and one of your buddies (don't try this) fired a bolt action centerfire with the buttstock on your back, it would most likely knock you to your knees.  

[Jamie Jackson]

Rich Davis is an innovative fellow.

He's been doing body armor demonstration for a number of years. It has made a huge impact (pun intended) on the rise of his Second Chance body armor company to becoming an industry leader.

 

Thanks for the vids Dolomite. And thanks for the excellent information and discussion folks. :up:

[peejman]

What they said.  The boxing vs. needle analogy is a good one.  It's all about the energy balance. 

 

A 0.308 bullet has about 0.075 sqin of area (consider it a cylinder rather than conical).  The shoulder stock of a rifle has roughly 3 sqin of area.... 40x more than the bullet. 

[Jonnin]

I will try to find the video. There is a guy being shot with a 308 at point blank to prove the armor works. He does not get thrown back like one would think with the amount of FPE a 308 has.

I do not believe FPE and kinetic energy are the same.

Dolomite

 

FPE (assuming this is foot-pounds of energy?)  is a unit, kinetic energy is a concept. 

FPE is a unit of kinetic energy.

[ShamGlock]

You come here to talk about guns....but you stay for the science threads!!!!!!!!!!!!!!!!!!!!

[broox]

I think we need a physics subforum.

[KaNuckles]

That's cool guys. Hope I'm not ticking anybody off.  I really like to discuss this kind of stuff. I appreciate the info very much. I'm no sure now that I've slept on it what I thought was going on. I just used the 50 as an example because of its "enhanced" performance compared to other rounds. The needle vs boxing glove makes perfect sense. But now I have another question.

 

Push vs. punch.

 

If a guy shoots, let's just say a 50 for effect, a rifle that weighs 10lbs, has a 26" barrel, has a buttstock with 4 sq. in. surface area and in no way absorbs recoil and he shoots it from a standing position. He shoots another guy whom on his shoulder has a 4 sq. in. buttstock made exactly like the one on the rifle that also has the same 10lb weight as the rifle. Both men are the same weight and build. Pretend they're in a vacuum and their is no loss of bullet energy. The round is fired directly into the 10lb buttstock on the target man. Would he not wind up with at least a badly bruised, if not broken, shoulder? The reason being not from difference in force applied to each man but because of HOW it is applied. The shooter has the force applied more gradually as the bullet is pushed away by the expansion of the gases. I know the explosion is instant compared to human reaction time or something, but it is still pretty gradual compared to an impact. The shoot-ee is being struck instantly without that same "buffer" or "push" if you will. The shoot-ee doesn't have those gases gradually bringing the bullet to zero from top speed in the last 26". However, the shooter DOES have that buffer, or gradual push from zero to top speed in 26". 

 

It's kinda like using a sledgehammer to push a cinder block with 100 lbs of force vs. hitting it with 100lbs of force. Say the hammer head is rested directly against the block and gradually brought up to mph and 100 lbs of force. The block theoretically would be accelerated to 10mph without any damage. Then figure the head singing mph. with 100 lbs of force striking the stationary block. The block would be cracked/busted.

 

BTW, I'm not trying to argue a bullet will send people flying. I do know better. But it seems like impact would have a little to do with it. It would seem the violence with which the energy is transferred would be greater on the receiving end and cause more damage. Penetration aside. 

Edited March 12, 2013 by KaNuckles

[peejman]

That's cool guys. Hope I'm not ticking anybody off.  I really like to discuss this kind of stuff. I appreciate the info very much. I'm no sure now that I've slept on it what I thought was going on. I just used the 50 as an example because of its "enhanced" performance compared to other rounds. The needle vs boxing glove makes perfect sense. It does bring up another question. Push vs. punch. If a guy shoots, let's just say a 50 for effect, a rifle that weighs 10lbs, has a buttstock with 4 sq. in. surface area and in no way absorbs recoil and he shoots it from a standing position. He shoots another guy whom on his shoulder has a 4 sq. in. buttstock made exactly like the one on the rifle that also has the same 10lb weight as the rifle. Both men are the same weight and build. Pretend they're in a vacuum and their is no loss of bullet energy. The round is fired directly into the 10lb buttstock on the target man. Would he not wind up with at least a broke shoulder? The reason being not from difference in force applied to each man but because of HOW it is applied. The shooter has the force applied more gradually as the bullet is pushed away by the expansion of the gases. I know the explosion is instant compared to human reaction time or something, but it is still pretty gradual compared to an impact. The shoot-ee is being struck instantly without that same "buffer" or "push" if you will.  Again, I'm not trying to prove that a 9mm (or even a 50 cal.) can send people flying through the air. I know better than all that crap. 

 

In other words...It's like using a sledgehammer to push a cinder block with 100lbs of force vs. hitting it with 100lbs of force. 

 

 

No problem.  Us nerdy types are usually happy to (attempt to) explain.  :)

 

I'm honestly not sure about your shooter vs. target question.  The shooter does absorb the acceleration of the bullet while the target absorbs it's deceleration (which technically doesn't exist... it's actually negative acceleration).  If both have exactly the same mass and effective spring rate (or energy absorption rate) and assuming no losses, conservation of energy would dictate the impact to both would be exactly the same.  Hence, no the target would not be hurt any more than the shooter.  Seems I talked myself into the answer, at least until someone shoots holes in my theory (bada bing! nerd humor  :D ).   Sounds like a great high school science fair project...

 

It's the penetration, tissue damage, and physiological reactions to being shot that does the work.

 

The "no losses" part is the trick.  When fired, some of the energy the powder transfers to the bullet is lost as heat generation.  Heat is also generated on impact and the bullet's deformation also absorbs some energy.  I've no idea of the relative magnitudes of these losses.  I'd guess they're pretty small and are likely negligible.  I'm sure there's some physics PhD ballistics guru that knows all this stuff. 

Edited March 12, 2013 by peejman

[Jonnin]

both men will have about the same shoulder damage.  Broken?  maybe.   I do not know what it takes to break a shoulder.    The bullet will gradually slow down on impact (either cutting into the target and stopping or smashing into it and crumpling or something), nothing is truly instant, just as the gasses etc accelerate on the shooter side.   I do not know the rates but nothing is instant, instant stuff is used to simplify physics but does not exist in the real world.  

 

Either way, both men would be hurting about the same -- both would be hit by "about the same" momentum across about the same surface area in the same anatomy etc. 

[TMF]

That's cool guys. Hope I'm not ticking anybody off.  I really like to discuss this kind of stuff. I appreciate the info very much. I'm no sure now that I've slept on it what I thought was going on. I just used the 50 as an example because of its "enhanced" performance compared to other rounds. The needle vs boxing glove makes perfect sense. But now I have another question.

 

Push vs. punch.

 

If a guy shoots, let's just say a 50 for effect, a rifle that weighs 10lbs, has a 26" barrel, has a buttstock with 4 sq. in. surface area and in no way absorbs recoil and he shoots it from a standing position. He shoots another guy whom on his shoulder has a 4 sq. in. buttstock made exactly like the one on the rifle that also has the same 10lb weight as the rifle. Both men are the same weight and build. Pretend they're in a vacuum and their is no loss of bullet energy. The round is fired directly into the 10lb buttstock on the target man. Would he not wind up with at least a badly bruised, if not broken, shoulder? The reason being not from difference in force applied to each man but because of HOW it is applied. The shooter has the force applied more gradually as the bullet is pushed away by the expansion of the gases. I know the explosion is instant compared to human reaction time or something, but it is still pretty gradual compared to an impact. The shoot-ee is being struck instantly without that same "buffer" or "push" if you will. The shoot-ee doesn't have those gases gradually bringing the bullet to zero from top speed in the last 26". However, the shooter DOES have that buffer, or gradual push from zero to top speed in 26". 

Ticked off?  That's crazy talk.

 

Don't take what Dolo said too literally... it isn't an exact science due to all the things you mentioned such as the weapon's buffering system, weight of the firearm and so forth.  But, if what you described could be recreated I don't see it being much different than felt recoil.  Once the bullet terminates in the chamber of the receiving weapon, all that energy is going to be transferred to that weapon before it is transferred to the shoulder of the firer, same as the firearm that it left.

[jdw174]

I attended Rich Davis' Second Chance Shoot in the early '80's.  He always demonstrated his soft body vest by shooting himself, point blank, in the chest with a .44 mag.  Spooky thing to watch.  That's why I wore a SC vest through my career.

[E4 No More]

I'll stick with Kevlar and such, thanks.

[peejman]

Push vs. punch.

 

It's kinda like using a sledgehammer to push a cinder block with 100 lbs of force vs. hitting it with 100lbs of force. Say the hammer head is rested directly against the block and gradually brought up to mph and 100 lbs of force. The block theoretically would be accelerated to 10mph without any damage. Then figure the head singing mph. with 100 lbs of force striking the stationary block. The block would be cracked/busted.

 

There's a lot going on in your example.  The magnitude of acceleration and the rate of change of acceleration (called the jerk) are involved.  There's a threshold beyond which a simple acceleration applied to an object becomes an impact.  Impact gets a little deeper and involves conservation of momentum, coefficient of restitution (elastic & plastic collisions), and impulse (a vector quantity).  You've also got to consider the mechanical properties of the block  and hammer (compressive strength, fracture toughness).  It gets busy.  This illustrates why engineering homework problems are so simple, and in turn why real engineering problems (that may seem simple) can be quite complex.   

Edited March 12, 2013 by peejman

[KaNuckles]

Ticked off?  That's crazy talk.

 

Don't take what Dolo said too literally... it isn't an exact science due to all the things you mentioned such as the weapon's buffering system, weight of the firearm and so forth.  But, if what you described could be recreated I don't see it being much different than felt recoil.  Once the bullet terminates in the chamber of the receiving weapon, all that energy is going to be transferred to that weapon before it is transferred to the shoulder of the firer, same as the firearm that it left.

I didn't take Dolomite's (or anyone else's) comments as being aggravated/offended. Just making sure everyone knows I am not questioning their knowledge or abilities. I am asking purely out of curiosity. One thing I've learned about debating on the interwebz is it is impossible to pick up on tone with typed words. I've seen the most innocent of comments get taken WAY out of context simply because tone can't be heard. So I always like to make sure I clarify my intentions. I appreciate Dolomite starting this thread. I have learned a lot and got some things clarified. 

 

I see exactly what everybody is saying. But don't expect me to voluntarily strap on some floor tiles to be tested for bullet resistance anytime soon.  ;)​ 

[TMF]

I didn't take Dolomite's (or anyone else's) comments as being aggravated/offended. Just making sure everyone knows I am not questioning their knowledge or abilities. I am asking purely out of curiosity. One thing I've learned about debating on the interwebz is it is impossible to pick up on tone with typed words. I've seen the most innocent of comments get taken WAY out of context simply because tone can't be heard. So I always like to make sure I clarify my intentions. I appreciate Dolomite starting this thread. I have learned a lot and got some things clarified. 
 
I see exactly what everybody is saying. But don't expect me to voluntarily strap on some floor tiles to be tested for bullet resistance anytime soon.  ;)​ 

Apparently there are some folks here that stayed awake in their Physics class.... I am not one of them.

[Jonnin]

. it isn't an exact science due to all the things you mentioned

 

 

It is exact if you have all 500+ variables.   Which is not possible under anything but the most scientific of projects, and not practical (expensive, time consuming) for such problems.   So we have to guesstimate a lot of the stuff, which leads to the answer being "approximate" --- sometimes, often times, very approximate and at times even unusable due to poor accuracy. 

 

That said, you can do  a LOT with a little, lol.  I once had to solve the approximate recoil of a shotgun from a video of it in action, that took me over a week as I had very little info.  Thankfully it was mounted on a tripod instead of human fired, or it would have been unpossible. 

[KaNuckles]

Well....Y'all win...I feel bad. I kinda feel like the thread go hijacked because of me so I apologize for that. Back on topic now. That is pretty amazing stuff. At my house if I were to have to defend it from my bedroom I would most certainly be pointing at my kids' rooms. That's always bothered me. Something like this has the potential to make a room "bullet retardant." At least some ideas can be sprouted from this. 

[peejman]

Well....Y'all win...I feel bad. I kinda feel like the thread go hijacked because of me so I apologize for that. Back on topic now. That is pretty amazing stuff. At my house if I were to have to defend it from my bedroom I would most certainly be pointing at my kids' rooms. That's always bothered me. Something like this has the potential to make a room "bullet retardant." At least some ideas can be sprouted from this. 

 

My house is the same way.  I'd never shoot that direction unless the kids were already behind me.  Far from ideal, but I have to go to them.

[Jonnin]

Apparently there are some folks here that stayed awake in their Physics class.... I am not one of them.

 

I found the second half, electricity and magnetism, to be exceedingly dull. 

 

I like the idea of using the video's concepts to reinforce the house.... a LOT....

[broox]

I still don't buy it.  you are telling me that any pistol that I can shoot strong hand only, you can go down range and catch that bullet with a kevlar catchers mitt?  And it won't break your wrist?

Edited March 12, 2013 by broox

[Magiccarpetrides]

Back to the OP

 

You could ghetto body armor a lot of different ways but those floor tiles stacked like that would be way too heavy to be practical for personal use or even vehicular.  Hell AR500 steel isnt all that much in bulk.

[Dolomite_supafly]

I still don't buy it.  you are telling me that any pistol that I can shoot strong hand only, you can go down range and catch that bullet with a kevlar catchers mitt?  And it won't break your wrist?

Yep.

 

If you take a single shot pistol and fire it at another person holding that same exact pistol and the bullet hits the second pistol and does not exit the recoil will be the same. Actually a little less because the bullet has slowed down between the two.

 

Newton's law is what says any reaction will have and equal and opposite reaction.

 

Dolomite

[kwe45919]

There's a lot going on in your example.  The magnitude of acceleration and the rate of change of acceleration (called the jerk) are involved.  There's a threshold beyond which a simple acceleration applied to an object becomes an impact.  Impact gets a little deeper and involves conservation of momentum, coefficient of restitution (elastic & plastic collisions), and impulse (a vector quantity).  You've also got to consider the mechanical properties of the block  and hammer (compressive strength, fracture toughness).  It gets busy.  This illustrates why engineering homework problems are so simple, and in turn why real engineering problems (that may seem simple) can be quite complex.   

 

My head hurts after reading that. You're just to smart for your own good. :pleased:

[peejman]

I still don't buy it.  you are telling me that any pistol that I can shoot strong hand only, you can go down range and catch that bullet with a kevlar catchers mitt?  And it won't break your wrist?

 

Why does an MLB pitcher not knock the catcher over with a 98 mph fast ball?  Same concept.

 

A baseball weighs 149 grams and travels at 98 mph.  Kinetic energy  = 0.5 x mass x velocity squared = 1135 ft-lbs. 

 

Muzzle energy from a typical .44 Mag = 1100 ft-lbs.  And Harry Callahan taught us all that a .44 mag sends people flying backwards. 

Edited March 13, 2013 by peejman