While reading the many caliber debates, 223 vs 7.62x39, the term "penetration against hard targets" is often brought up. On the surface it makes sense, and the 7.62x39 is always touted as the winner in this category, while the 223 is better on soft targets. All sounds good so far, but what is really meant by "hard targets"?

Here's why I ask. I dragged a piece of steel out to the country once for a little experiment. I can't remember for sure, but the steel was somewhere in the neighborhood of 3/8 to 1/2 inch thick. I shot it with a HP 7.62x39 round, and the bullet just splattered - there was a faint grey smudge where it hit, and possibly a small, small indentation. Then I tried it with a lead core FMJ 223 out of a 16" bbl - this time there was a 22 cal crater about halfway through, it even had opened up a seam on the backside where it tried to push it's way out. So wouldn't that mean 223 wins against hard targets?

I would like some more understanding as to what a hard target is. A brick wall, a car door, a windshield, what?

thats because you used hollow points on the 7.62x39 that it went splat, try this quarter inch steel both using fmj rounds, look at the difference. the really big difference is what happened to the wood behind the steel, the 223 left a slight larger hole in the wood than the steel, the AK however left a hole in similar size than a 12 gauge slug going thru the wood AFTER the steel.

[img]http://mywpages.comcast.net/erouls/steel.jpg[/img]

edited to add that this is the impact side ofthe steel, funny how the metal mushrooms out like a water drop, supposedly this is because when metal is struck by a high velocity object it acts like a liquid, like a water droplet hitting water, pretty neat when u see it in slow mo.

Thing is, defeating "hard" targets like certain thicknesses of armour plating, velocity is king.   No matter how light in mass, push it fast enough and you'll make things fail consistently more than something heavier and slower.    I've even found that construction of the bullet doesn't matter as much as one would think, the jackets appear to melt and shed away within the first moments of impact with a large majority of the damage being done by the lead core.    For comparison purposes I've put 55grn exposed lead tip spire points through the same mild steel as my 55grn FMJ loads and had both defeat the steel.


I've had 5.56x45mm smoke though things that a 7.62x39mm wouldn't make it all the way through, what made a LOT of the difference was the 3300fps muzzle velocity of the 55grn round as opposed to barely 2200fps out of the 123grn 7.62x39mm.

Weight helps a little too but if you can't get it movin fast enough you can't liquify enough of the steel down range.

Now for deflection, the 5.56x45mm can be deflected much more easily due to it having lower mass compared to that of the 7.62x39mm weighing a good 2x more.

id have to say the construction of the bullet does matter. With the FMJ or most types of bullets yes the copper jacket is left or shed off but the steel core punches thru, this is not the case with hollow points. Hollow points mushroom out dissapating energy and creating a larger surface area decreasing the pressure per square inch.

velocity is very important but so is mass, remeber velocity x mass are equal factors.

our police dept. did some shooting into body panels and car doors.  we used an Escort door, i think.  anyway it was from a car not built before 84.  They ysed real steel then.  we were trying to simulate what hitting cars that are on the road now would be like.

our .40 cals zipped thru the door w/ no problems.  the .223 (55grain federal) and some of the guys .308 had no problem as well.  glass is a little different, but all went through with secondary fragmentation from the glass.  The point of aim changed thru glass due to glass bending light (angle of incidence, i think) and the glass changing the direction of the bullet.

For our purposes, all rounds used will easily defeat body panels and glass.  Engine blocks and steel rims are different, of course.

Hope this helps...as far as a true definition of "hard targets"...IMO, that is up to you and what you have to address with your rifle, etc.

Mass and velocity are only equal in calculating momentum. In energy calculations, velocity is squared.

Therefore, speed is a larger factor in the amount of energy delivered to the target.

And yes, contruction of the bullet does matter. It makes a large difference on how that energy is transferred to the target and what momentum is retained.

I also have to agree with tango_down, "hard targets" are defined by your own unique situations.

Jonathan

Troy is exactly right.  Assuming "armor piercing rounds" are for body armor is just what my dept. did.

Our .223 and .308 will pass through most body armor, except the heavy swat type stuff.  Our dept issued AP rounds w/ our rifles.  there is also a policy regarding use of AP rounds against targets with Body Armor.  Of course the policy gets vague at the end and leaves it open to use AP against "hardened targets".  Questions about what constitutes "hardened" left us with answers from admin office like, barricaded subject behind cover, in a vehicle, or heavily armored, etc.

I'm not complaining about being issued AP, but unless the bad guy is hiding in a garbage roll-off or something, or driving some stolen vehicle from the Nat. Guard Armory, I'm not using the AP stuff.