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BeyondTheBox 10-03-2012 11:08 PM

HP expansion/balistics question(s)
So I've got a 9mm two shot derringer I use as a backup carry piece. I've been told that, due to the short barrel length, there wouldn't be enough velocity to cause an HP to expand from such a handgun.

My main concern, when considering defensive firearms, is safety. Not for myself, but, rather, for those around and in possible danger of an over-penetrating round. So I've started carrying lower calibers, but I do see the possibility of a need, in a unique occasion, in which some hopped up druggie might require a more persuasive nudge, thus the backup.

My question is, if the velocity from my derringer is so much less, should I even bother worrying about over-penetration? Or how can I test this myself without paying a crazy price for balistic gel? Not sure what it costs, but guessing it's up there.

Also, isn't the point of an HP to reduce chance of over-penetration? Is what causes the round to open the resistence received from its coursing through the air or the contact with its target? If it's the air, then wouldn't it be reasonable to assume that the impact with a body too could create that necessary resistence, allowing it to open and still serve its purpose, regardless of barrel length and/or velocity? If not then I understand.

I'll fully admit it, I'm very inexperienced and unknowledgable when it comes to balistics and all this, hence my being here. How I'e come to my theory above is simply through a novices attempt at logical thinking. Hahaha

Speak some knowledge at me; take me to school fellas!!!

Thanks inadvance!

JTJ 10-03-2012 11:16 PM

1 gallon water jugs in a tight line (touching) will give you an approximation of expansion and penetration. A 1 gallon water jug is about 5" across. 2 jugs is roughly equivalent to 5" of penetration. 4 jugs = 10". Hang a couple of layers of cloth in front of the 1st jug.

BeyondTheBox 10-03-2012 11:32 PM


Originally Posted by JTJ
Hang a couple of layers of cloth in front of the 1st jug.[/URL]

Ahhh, to simulate a clothed attacker. Good advice/thought. Thanks man. Can I assume milk jugs refilled will do?

CHLChris 10-03-2012 11:40 PM

Milk jugs is exactly what he meant. Another way would be to borrow someone's chronograph, if possible. Then check velocity against what the box says it should be out of a normal barrel. A LOT less and you'd probably be able to bet on lack of penetration.

I would skip all of that, myself. Just get a HP that has a polymer insert to aid with appropriate penetration before it expands, if it expands at all. I'm talking about Hornady Critical Defense/Duty or their Zombie Max (exactly the same thing, but green tip.

BeyondTheBox 10-03-2012 11:53 PM

Great ideas, I love it.

One reason I bought this little thing was because I knew it would fire any round that fit in the barrel. With no ramp or magazine there's no feeding to worry about! Figured it would eliminate any possibility of pickiness with ammo, didn't figure on it having an issue with actually expanding. Hahaha

Thanks a million for the tips and tricks guys. Solid and very helpful info here!

robocop10mm 10-04-2012 12:41 AM

I believer Speer makes a special load for short barrels. I know they do in .40.

SSGN_Doc 10-04-2012 01:22 AM

And just to help answer you questiona bout the mechanism of action that causes HP bullets to expand:

It is largely a function of hydraulics. Liquids don't compress so whe a HP bullet gets into flesh the water in the tissue cells gets into the cavity of the bullet and pushes outward on the core and jacket and cause it to bend and tear and in some case to fragment. Bullets are designed for caliber load by material selection and jacket tickness in areas to help ensure expansion will happen is a certain velocity range so that bullets retain weight and don't fragment like they would if they went too fast. If the bullets are drivven to slow they may not generate the hydraulic force needed to get reliable expansion. This is also why bullets are often tested with denim in front of testing media as well, because if the hollow point is clogged on it's way into the body there my not be enough fluid and hydraulic force to get the bullet to expand reliably either.

BeyondTheBox 10-04-2012 01:43 AM

Awesome explanation doc. Thanks for that.

BeyondTheBox 10-04-2012 01:44 AM


Originally Posted by robocop10mm
I believer Speer makes a special load for short barrels. I know they do in .40.

Okay, good tip man, I'll look into that some more, thanks.

BeyondTheBox 10-04-2012 01:59 AM

So doing this jug test, I assume I'd stand the standard 10ft from target when firing. Should I place something solid behind to catch in case it goes straight through, or just a second jug good enough?

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