Ballistic testing and Best way to nicely expand jhp ammo ??

[EastSideRich]

I want to get a bunch of nicely expanded (fully and evenly) jhp bullets (handgun calibers).
In the process I was hoping to do my own little round of ballistics tests, looking at penetration, expansion and consistency between various makes and caliber ammo.

Recently I had the good fortune of getting a hold of what I thought was a very promising material for this, but now I'm wondering if it's not going to work - I have no idea why.
I was able to bring home a 25-30 lb block of an acrylic hot-melt adhesive that was going to go in trash at work. It has fantastic viscoelastic properties and is extremely sticky. This stuff is very tough and rubbery, but will flow given enough time, taking the shape of whatever container it's in (kinda like silly putty, but stiffer). I figured this would be an ideal material for ballistic testing, its toughness and tack limits penetration (for example if you stab it hard with a flat screwdriver you can only get it about an inch or so in), its viscosity allows it to seal up holes, so it's reusable, and it's very homogeneous so it should be excellent for comparing different ammunition.

The limited "testing" I've done with it so far is as follows:
.177 steel bb, 400 fps: sticks to surface.
.177 lead pellet, ~1000 fps: 1-1.5" penetration, decent expansion depending on pellet type.
.22 Federal high velocity hollow point, 36 gr, velocity??, out of 4" bbl revolver: ~4-5" penetration, no expansion.
9mm Remington UMC JHP (can't remember bullet wt), out of 4" bbl passed through ~6" block, no expansion (bullets mangled in backstop)

Heres the one that surprised me most:
.40 Hornady TAP, 155gr, 1180fps (stated on box), out of 3.9" bbl: ~8" penetration, minimal expansion.

All bullets impacted a flat face of the block at a 90 degree angle.
All bullets went perfectly straight through medium, don't appear to have tumbled, and left no cavity other than a path the diameter of the projectile.

Just for fun heres a pic of the results:

Heres my question(s):

What is the best way to get fully expanded bullets without damaging them?

Also, any thoughts as to why my "ballistic gel" isn't performing as expected?

 

[Sidetracked]

Water... Water... Water...

Water jugs tend to produce wonderfully mushroomed bullets. Other posters may have other suggestions. I stick to water, since it is cheap.


As to your issues... I really don't know. It could be the container you have the stuff in, or it could be the elastomeric properties of the substance itself. It may be too hard to begin with, or turn itself into a concrete-like medium upon compression. There is no good way to tell without a lot of information.

 

[BurkGlocker]

Water or homemade gelatin. I used water for years, but saving milk and water jugs became too much of a hassle. Finally I made my own 'ballistics' gel, and have used the same batch for numerous tests. MOF its still in the fridge awaiting its next date with destiny. Its just as easy as melting it down and reforming it when you need it. You can find quite a few sites online that describe how to make it, and if and when you do, it sure is nice to see the destruction left in the gel whereas water only expands them. Mind you it wont be a 'calibrated' test, but its still fun and will serve its purpose.

+1 to Sidetracked's deduction on your test material.

 

[EastSideRich]

This may be a dumb question, but

Why wouldn't a harder medium cause more expansion?

The stuff is pretty firm; if you hit it hard with something, there is little give (feels quite solid). If you just push it with your finger or something, it's a little squishy.

 

[Rampant_Colt]

JHP ammunition bullets function using fluid dynamics, or hydraulics.. AKA water.. "Hydra-Shok"

for me, soaking wet newspaper gives consistant repeatable results, and accurate penetration depth. I've hundreds of recovered bullets from wetpack

if wetpack isn't possible, try using a "Fackler Box" [google it]
you use a 6' x 12" wooden trough and fill it with as many water-filled Ziplock storage baggies that will fit

 

[Sidetracked]

I have found HP bullets, no matter what quality level, tend to expand like the ones you have pictures when they hit a solid medium or a medium that doesn't lend itself well to shock-compression. If they don't match your picture, they have completely fragmented. (In my experience)

A good example of something that seems like a good medium, but is really terrible; is the common science experiment from elementary school classrooms. The "Cornstarch Suspension" might lend some insight, if you have never seen it before.

Common pottery clays tend to do well, if you have a large enough quantity. I still prefer water, though.

 

[EastSideRich]

I still dont get it.

As far as I know, water like any liquid is incompressible, even at the ridiculously high pressures involved with a bullet. I think the only difference between water and my block of stuff is the viscosity and the elasticity of my medium. My intuition tells me this stuff should work just like ballistic gelatin but with less penetration, and I would think more expansion. This stuff should "push back harder" on the bullet than the gelatin, which I would think would cause greater expansion; not to mention the tackiness of the material, which I would think would help create more drag on the petals on the front of the bullet, pulling them back even more.

This so far does not seem to be the case.
I am guessing somehow this stuff is catching the bullet instead of stopping it, if you know what I mean.

If there are any fluid dynamics or physics experts here I'd love to hear your theory about this.

Anyway, as the consensus seems to be water works best, I think I'll have to come up with a method for doing this.
I'm really bummed out about this because I thought I had gotten a hold of the perfect ballistics testing material.

As an aside, this is totally off topic, but if anyone wants to see a really cool demonstration of a shear thickening fluid (cornstarch in water), check this video out.

If you do watch it, make sure to watch to the end (it's only a couple of minutes long)

 

[deranged]

By no means am I a fluid dynamics or physics expert, but I do have a couple of answers for you.

You are correct, water is incompressible. However, water is also for more fluid than the material which you are using, meaning it moves. Water takes the shape of whatever container it is in, like all fluids. You material will too, but over an exponentially greater period of time.

The material you are using it too hard, so like you said, its catching the bullets. Its not hard enough to cause any ricochet, pliable enough to absorb all of the bullets energy in a short matter of time. Whereas when the bullet hits the container of water, it immediately grants a hole for the water, and built up pressure from the impact, to escape, as well as the water having far less viscosity than the substance you are using, so the water moves out of the way, but still slowly absorbs that energy from the bullet, and offers enough resistance to mushroom the bullet.

Think of your screwdrive example, you jab a relatively small pointed object into the material, and it only goes in about an inch. Do that in water, and you can insert the screwdriver as far as your arm can keep pushing it. Same goes for ballistics gel, if you were to stab it with a screwdriveer, it would go in farther than an inch. And, to get a similar effect out of water you need two things, more water=higher surface tension, and more surface area on the object impacting the water. Think belly flop, you slow down quite a bit when you first hit the water don't you.

Maybe that helps? Hopefully I didn't dumb it down too much.

 

[EastSideRich]

I think I figured it out. I think the medium I have is basically pushing on the outside of the tip of the bullet hard enough that it negates the pressure inside the open end of the bullet. In water, the fluid in contact with the outside of the projectile can "slip" past it, while the fluid inside the little cone has no where to go, and the pressure causes it to open. In my stuff, either the viscosity or the tackniess keeps it from smoothly moving over the outside of the bullet, i.e. it pushes on the outside as much as the inside of the opening, thus preventing expansion.

The solution I came up with was to put a little water at the front of the medium to initiate expansion. After that my stuff should work as expected.

Heres the set-up I tried - a sandwich bag of water stuck to the front of a few layers of my adhesive (it's sticky enough I can just stick the bag to the front).

It worked beautifully. After going through the baggie (about 2-3 inches of water), the rounds fully expanded and only penetrated only about an inch or two into the layers of polymer. Here is a couple of pics of the results. The ones towards the top are from before using water (un-expanded) the ones towards the bottom are after. .40 TAP is on the left, .9mm UMC is on the right.

I know this is probably not an accurate representation of tissue, but it's kinda fun.
The .40s only went about three inches into my stuff (just penetrated the white layer of plastic and were resting on the second layer of adhesive) , the 9mm went about two inches into the first layer.
I guess this is my own little Box 'O Truth.

It's kinda nice because there's not much water to clean up (as opposed to 5 or 6 jugs of water, or a whole bunch of gallon ziplocks), and the whole thing it only about a foot and a half long.
Maybe I'll post more "scientific" results once I get a couple more different brands of ammo and have the time to satandardize or "calibrate" my box.

p.s: Don't worry about dumbing it down for me. I have taken courses in physics and fluid mechanics and have a bachelors degree in chemical engineering - I am capable of understanding this stuff.

Also, sorry the pics are so big, I cant get them to show up smaller.

 

[Sidetracked]

Very cool. I'm glad you found a compromise that works well.

 

[nutty ned]

.40 Hornady TAP, 155gr, 1180fps (stated on box), out of 3.9" bbl:

I've had bad results with that bullet also, but, all test mediums are not equal.