shorter barrel = more penetration?


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SnakeLogan
November 23, 2008, 06:20 PM
http://www.texassmallarmsresearch.com/Info/556Performance/556Performance.pdf

When the 77 gr SMK was fired from a 16 inch barrel, the bullet didn't even reach 12 inches in ballistic gel. When fired from a 14.5 inch barrel, it went more than 15. My theory is the more penetration the better. Right now I'm using a 20 inch barrel. Should I go to something shorter for more penetration?

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rcmodel
November 23, 2008, 06:25 PM
What exactly is it you want to penetrate?

12" is enough to kill two people stacked prison-lover style!

Was it me, I'd go for all the velocity I could get. That is what causes the bullet to self-destruct and cause the most damage inside the target, where it does the most good.

Total penetration might be good for shooting through heavy cover, but bullet blow-up inside the boiler room is what makes the target DRT.

rcmodel

woof
November 23, 2008, 06:29 PM
I'm trying to think of what bit of physics would cause the same bullet coming from a shorter barrel to have more penetration?

gvnwst
November 23, 2008, 06:30 PM
The shorter the barrel, the lower velocity. With such a low velocity, the bullet couldn't open up as much, resulting in more penetration. Or that is my guess, i can t find the test in those pages.

R.W.Dale
November 23, 2008, 06:33 PM
I'm trying to think of what bit of physics would cause the same bullet coming from a shorter barrel to have more penetration?

less velocity = less rapid bullet expansion resulting in more penetration. This actually can be quite common with many cartridges

Z71
November 23, 2008, 06:41 PM
Ballistics are strange. Generally shorter barrels mean less velocity, which equates to less energy on target. However we are talking mil spec ammo here.

I would take these results with a grain of salt. True, a higher velocity bullet may fragment quicker resulting in less penetration, but that might mean more energy dumped on the target. A bullet that zings right through the target spends it's remaining energy beyond the target, not inside it.

A lot depends on the bullets used.

Generaly, longer barrels mean more velocity, which means more range. Another advantage, with iron sights anyhow, is a longer distance between the front and rear sights, meaning better accuracy.

Short barrels have been adopted on the M4 more for convenience to the troops carrying the gun. Vehicle mounted troops requiring shorter guns than the foot propelled infantryman of old. I doubt the military had bullet performance in mind when adopting the M4 carbine.

Lots of variables in ballistics of a cartridge, but generaly for every inch lost off a rifle barrel equates to lost velocity and energy too.

As an example of sorts, a hollowpoint .308 from a rifle might explode on contact with the target. But an armor peircing bullet may penetrate the target, the targets house, the neighbor, the neighbors house, and then some! Penetration ain't always good!

lipadj46
November 23, 2008, 06:48 PM
If you are trying to put down an animal efficiently would you want more penetration or would you want your bullet to mushroom and/or fall apart faster at higher initial energy? I think I would go for higher velocity and bullet expansion but that is just me and I'm no expert. My thoughts are that the higher velocity bullet has more kinetic energy and if it is penetrating less that energy has to go somewhere, the bullet is mushrooming, falling apart and causing trauma. I know there are a couple schools of thought on this though and like anything else everyone has a opinion.

jmr40
November 23, 2008, 06:50 PM
Yes, velocity is the key. At longer ranges the faster bullet would have slowed down and would have had better penetration. Under the right conditions it is not uncommon for a 30-30 to penetrate better than a 300 magnum for the same reasons. Bullet construction is another factor as well.

SnakeLogan
November 23, 2008, 08:42 PM
Total penetration might be good for shooting through heavy cover, but bullet blow-up inside the boiler room is what makes the target DRT.

Being able to reach the spinal column is the only way to make the BG DRT.

gvnwst
November 23, 2008, 08:43 PM
That is what, 8"-10"? Not past 12".

HorseSoldier
November 23, 2008, 10:02 PM
When the 77 gr SMK was fired from a 16 inch barrel, the bullet didn't even reach 12 inches in ballistic gel. When fired from a 14.5 inch barrel, it went more than 15.

If you look at the gelatin shots shown, the longer barrel resulted in a more catastrophic failure of the bullet when it began yawing, producing more fragments. More and smaller/lighter fragments will not penetrate as deeply as larger/heavier ones (and neither will penetrate as deeply as an intact bullet), but will produce more wound tracks and give you better odds of perforating or severing something significant enough to be a rapid fight stopper.

(As a side note, the PDF you linked too looks to be based on Dr Gary Robert's work, with the advocacy of 6.8mm Rem SPC removed and enthusiasm for very heavy tungsten 5.56mm substituted.)

Being able to reach the spinal column is the only way to make the BG DRT.

The spinal column is pretty much a zero percentage shot with a service rifle or carbine under normal shooting conditions -- hitting it is ideal, but it's pretty much just luck. Best strategy to end a fight fast is to inflict massive trauma on the thoracic cavity.

SnakeLogan
November 23, 2008, 11:02 PM
The spinal column is pretty much a zero percentage shot with a service rifle or carbine under normal shooting conditions -- hitting it is ideal, but it's pretty much just luck. Best strategy to end a fight fast is to inflict massive trauma on the thoracic cavity.

Then shouldn't we all use shotguns for CQC home defense?

gvnwst
November 23, 2008, 11:03 PM
have you noticed that the shotgun is the most recomended HD gun of all time? That is for the reasons stated.

SnakeLogan
November 23, 2008, 11:28 PM
have you noticed that the shotgun is the most recomended HD gun of all time? That is for the reasons stated.

Maybe I just spend too much time on AR15.com :p

plinky
November 24, 2008, 12:09 AM
Matchkings are probably not the best bullet if you need textbook terminal performance. Expansion and penetration can be unpredictable. Sierra will pretty much tell you that.

I'm sure that sniper types use them, but only if shot placement is such that terminal performance is virtually irrelevant.

Ridgerunner665
November 24, 2008, 12:18 AM
I assume you are shooting a 223 Remington (AR 15)...if so, read on.

If you want penetration...use Barnes 70 grain TSX bullets and push them as fast as you can. Those suckers are wicked...

MT GUNNY
November 24, 2008, 12:34 AM
That Link has a lot of stuff to process. Could someone put that in coyote terms from a 16" barrel and a 24" . Is it telling me to go to a 77grainer in the 16"er and stick with a 62 in a 24"er. At all distances capable of a 5.56

HorseSoldier
November 24, 2008, 12:44 AM
Then shouldn't we all use shotguns for CQC home defense?

As long as you know you're going to be shooting at targets at pretty close range, I'd say there's a lot to be said for shotguns and buckshot.

HorseSoldier
November 24, 2008, 12:53 AM
Double Tap

RyanM
November 24, 2008, 01:16 AM
That is what, 8"-10"? Not past 12".

Skin is tough enough that it counts as 2" of jello, as a general rule. Not to mention ribs.

Anyway, you may want to consider a different load instead of a shorter barrel. Dr. Roberts, at least, considers Hornady 75 gr and Nosler 77 gr OTMs 1st tier for 1:7 barrels. The 77 gr SMK is a somewhat distant 2nd tier.

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