Bullet expansion, or not!

[London Best]

Someone asked me a question the other day, which I was unable to answer satisfactorily. Perhaps one of you on here could help. 
He said, “When I shoot a 58 grain V-max at a fox or any other animal from my .243 the bullet expands, a lot. But if I shoot it at the side of a waste disposal skip it drills a neat hole straight through. Fair enough, but what I cannot understand is that the bullet will traverse the width of the skip, seemingly intact, and drill an equally neat hole through the opposite side. Can you explain how the soft bullet can stay together and do that?” 
I had to confess that I was at a loss to offer any explanation.

[Dougy]

I would bet that the entry and exit holes are created by 1st the entire bullet and the exit, by what would be left of the more solid base, the bit in-between i would imagine there would be B all left of the original bullet. 

When shooting steel targets even mild steel the Vmax fragments will cut the ground level with the target and depending on what steel (not hardox) continue through the steel making a hole. 

[Ultrastu]

Softer steel targets that get penetrated  have a tendancy to actually make a projectile smaller  diameter wize .they round over the tip making it great for pentrating the second skin of the  steel box or skip etc .

Expansion of a projectile .comes with high  speeds .and a gradual but constant slowing down through the medium (think all the  ballistic gel vids u have seen)3mm of steel or hard plastic etc  doesn't do this .

So yeah a fox will expand a bullet where thin  steel  sheet won't  .

[enfieldspares]

3 hours ago, London Best said:

Fair enough, but what I cannot understand is that the bullet will traverse the width of the skip, seemingly intact, and drill an equally neat hole through the opposite side. Can you explain how the soft bullet can stay together and do that?” 
I had to confess that I was at a loss to offer any explanation.

Ask the Germans in WWI who discovered that if they fired their rifles at British tanks little would happen except the tank would get ever closer. So, somehow, "they" discovered that if they pulled the bullet and reversed in in the case (so it fired out the barrel base first) it would penetrate the thin armour and enter the tank. So how does this work? Apparently the jacket holds the soft lead core together and pushes it through the armour plate.

Or maybe something else is happening with the OP's .243 bullet at the velocity it has when it meets the metal? As a kid I remember an explosives lecture at school where a wax candle was loaded in a musket and fired through an oak door. Something to do with the velocity being such that the molecules or whatever in the candle did have enough time to remember that they ought to squash flat instead of shoot through?

Now vice versa. I glue the bare bullet by its base to a wooden dowel and take a hammer to it like a stake through Dracula's heart the opposite happens. You could hammer the bullet through a captive fox and it would not expand (even when hitting the rib bones) but instead penetrate right through the poor animal. Yet hammer it against the steel skip and it flattens into a big lead copper coated disc.

So it's all about the velocity when it hits its target. There must be a different critical speed for BOTH the fox and the skip where the bullet expands, or doesn't expand and where the bullet instead remains "held together" by its jacket and penetrates. One the fox low speed = no expansion yet on the skip low speed = expansion.

Edited October 21 by enfieldspares

[TIGHTCHOKE]

Physics.   

[London Best]

2 hours ago, TIGHTCHOKE said:

Physics.   

Yeah! 
I dropped physics after a couple of years as I just couldn’t make head nor tail of it.

[JKD]

2 hours ago, TIGHTCHOKE said:

Physics.   

Would you like to expand on that ? 🤓

[bishop]

i shot a couple of roe with 243 vmax last season. both  clean kills ,dead on the spot.however the rounds went right  thru. They did not break up as i was advised they should.

[enfieldspares]

5 hours ago, TIGHTCHOKE said:

Physics.   

I like that. To the point. Explains why. Sorted.

And the next question for today please is....?

[wymberley]

Could it be anything to do with the amount of energy expended and absorbed by the bullet? Total energy expended and bullet stays in target - expansion. Relatively little energy expended as bullet carries on regardless with very little distortion. In other words; I don't know.