physics question on small bores

[mjbgalt]

i shot an EMPTY gatorade bottle, 20 ounces i think...not the huge one they sell...at about 50 yards with my .204 Encore. i shot three times and was pissed because i thought i must have missed and that my scope got knocked out of line somehow. i walked up to the bottle and picked it up and saw three holes right through it. now wouldn't you think a bullet would knock an empty bottle off the top of a cardboard box?

i know the bullet was moving damn near 4,000 feet per second but c'mon, it should have been enough pressure to move the bottle, right?

i was using the factory hornady load, a v-max bullet. shouldn't it have expanded at that speed? there were two holes for each shot, one in and one out. same diameter. this suggests that the bottle was not enough resistance for it to expand. now grab a plastic bottle and push in the side with your thumb. that feels pretty damn tough doesn't it. so tell me how then that the same bullet out of the same gun turned a rabbit into a pile of guts? that soft skin sure didn't put up much resistance.

just something i have been wondering about. my brother and his friends witnessed this bottle incident and none of them believed it either, until they saw the holes and then we had a collective "what the hell??" conversation.  


-Matt

[killdeer]

Once the bullet penetrates the bottle, there is no medium to send a pressure wave through except air.Now fill it with water and try again.

[mjbgalt]

i understand that part but what i am saying is, isn't the idea that x-amount of force back against the bullet causes expansion?

-Matt

[Qaz]

MJ, the bullet just burned through the plastic container like a hot needle, and so quickly the bottle had no time to react. That 204 will shoot through a steel plate, not from force alone but by force and tremendous heat from the rpm's of the bullet.

[Don Fischer]

Get two pop bottles, glass. Set the first on a table and on top set a dollar bill. Now stack the second bottle upside down on the first; Match up the opening's. Now try to pull the dollar bill out, you can't without knocking off the top bottle.

Re-stack the bottles with the dollar bill in there. This time hold a little tension on the bill. Very quickly hit the bill with the edge of your other hand while maintaining the tension. The bill will come right out without knocking off the top bottle.

Pretty much what happens when a super fast bullet hits very thin plastic with nothing inside to slow it down. Do the same thing with a 22 RF and the plastic bottle should get knocked over. The bullet goes so slow that the air inside the bottle tries to displace faster than the bullet can move. Fill it with water as killdeer said and the bottle will rupture badly as the water offers more restence than air.

[Game_Stalker]

I had this same thing happen with my Win 94 in 44 Mag. There was a cup or 2 of water in the bottom of the gallon jug, but I thought I had missed until I walked up to it. One in, one out.

With your .204, you've got to understand that there needs to be some kind of consistency in the resistance. I doubt the air alone would be enough to force any kind of continued expansion. The bullet may very well have begun to expand, but with those kind of speeds and no consistent resistance, the tip wouldn't have expanded beyond that 20 caliber bullet's widest diameter.

[corbanzo]

The expansion doesn't have to do with the transfered energy, expansion only makes the channel bigger in an animal.  When you are turning a rabbit into jelly, that is the expansion of energy from the bullet through the flesh of the animal, where the animal is resistance, and therefor the bullet will lose speed, and that energy is transfered outwards as a shockwave through the animal.  The expansion can slow the bullet more with more surface area, but only if it is hitting flesh.  When you see that type of damage on an animal it is a very fast moving projectile with a quick energy transfer.

[Selmer]

A projectile will only transfer its energy if and only if the target offers enough resistance to cause the projectile to transfer it's energy to the target.  The reason that you had clean pass throughs with no apparent reaction from the target is the simple laws of intertia.  The bullet is a small projectile moving at a very, very high velocity.  The bottle in this case is a thin-walled target that is stationary.  The law of inertia says that objects in motion want to stay in motion, and objects at rest want to stay at rest.  Your bullet encountered a stationary object that did not provide sufficient resistance to have a visible effect on the bottle OR the bullet.  The bullet did not "burn through the bottle because of heat generated by the incredible rpm's of the bullet"  Sorry Qaz, you're incorrect in this statement.  The dollar bill example was another example of intertia explained a different way.  The reason that this changes when we fill the bottle with water is that when liquids are impacted at a high velocity, the liquid's viscosity (thickness for a simple explanation) sky-rockets and resists the bullet passing through it, thus resulting in an explosion caused by transfer of energy.  Energy is mass x velocity squared. Two projectiles can have the same amount of energy, even if they're vastly different in weight, as  long as the lighter projectile is moving much, much faster, because it gains its energy from the velocity squared side of the equation.  A heavier, slower bullet will retain its energy better because it gains its energy from the mass side of the equation, which is going to stay relatively constant, even on impact.  The lighter bullet has mass that breaks up on impact and slows down, therefore transferring its energy into the target, whereas the heavy bullet keeps on going.  This is the basis of the Taylor Knock-Out formula as I understand it, and it makes sense to me.  A .204 Ruger bullet might have less energy than a 300 gr. .45 caliber bullet at 1600 fps, but creates a more visual impact because the .45 caliber bullet has more mass and will pass through and retain more energy on the other side, where as the highly frangible light bullet transfers the majority of its energy to the liquid, thus resulting in a highly pleasing visual effect.  Yes folks, it is fairly simple physics, I learned it in high school...
selmer

[AZ223]

I agree with Selmer; the empty bottle doesn't offer enough resistance and the bullet is moving so fast it's able to penetrate the bottle without resistance. I've had it happen with a 9mm semiauto pistol; thought I had forgot how to shoot until I went and looked at the bottle -- six holes; three in and three out.

Fill that bottle with water and hit it with a .223 at about 50 yards, and all you'll find is a wet spot and the ground and several pieces of shredded plastic. 

[poncaguy]

I've done the same with a 17 HMR'''''''''now, if you fill it with water........

[corbanzo]

I don't know if this really counts.... but last weekend we compared the .458 Lott to the .30-30.  Bottles full of water.  Guess what?  .458 made big water baloon.  .30-30 made medium water baloon. 

One of our favorite things to do:  (Kids, don't try this)

Mix gas and styrofoam to make napalm, pour into glass jug, light on fire, shoot with large gun.  Only in a rock pit, believe me.  Results?  Really good film making. 

[Selmer]

corbanzo, definitely sounds like fun, but I'm still young enough to remember what I would have done in high school, your napalm target would have been one of them.  I know you said don't try this at home and only in a rock pit, but unfortunately hormones and guns make for stupid decisions some days, I'm not sure it was real wise to post this target suggestion, but I might try it in a rock pit some time!
selmer