Home Forums Hunting & Shooting Ask The Gunwriters Bullet penetration in steel, comparisons...?

On another forum there is a discussion ongoing about bullet penetration in steel. A couple of guys say that high velocity and small caliber, their example is a .223, will out penetrate something like a .308 in steel plate. The argument is that the smaller caliber offers less resistance to the steel plate and the high velocity is more important than the greater momentum and energy of the .308. Also that the greater diameter of the .308 works against it in such a penetration test. I can sorta go along with that, except it seems to me that the military usually lays down the 5.56mm for the 7.62 when they want more penetration against light armor. Right now I'm thinking about insurgents in Iraq using car bombs at roadblocks. From what I gather the 5.56mm SAW failed to chop up oncoming vehicles and disable them, so the roadblocks went to 7.62 weapons systems at such stations. I guess the .50 BMG would be better yet!

Second part of the discussion centers on a statement made by one of the paticipants that bullet construction does not matter in steel plate penetration. In other words, a highly fragile 55 grain varmint designed hollowpoint, or plastic tip V-Max, Ballistic Tip, varmint bullet in a .223 will penetrate as well as a FMJ (not steel core) or a strongly constructed controlled expansion bullet such as a Barnes X. This I cannot get my head wrapped around. That doesn't seem likely to me. Can someone shed some light on the subject?

Velocity is the most important factor in pentrateing steel,but a FMJ and exspecialy an armor pierceing round of equal velocity will out penetrate an expanding bullet of the same speed. A 30 cal bullet of the same speed and construction as a 223 bullet will penetrate steel equaly well..........

On my steel gong my 22-250 AI leaves a deeper crater with 50 grain Vmax, than my 30-06 with 165 Interbonds. There is about 900 FPS difference in velocity though.

Ah, yes... Would explain why military ball ammo is useless for hunting...

I would go with the bullet construction does matter argument - as long as its a soft bullet. Example: I have steel plates of varying diameters on chains at my Dad's range. The plate is 3/8" thick. We rountinely shoot at them off hand for fun. There are only 2 holes through them, I put both of them there with the same gun - a 300 WM shooting 180 Sierra's under a max charge of RE 22. Muzzle velocity ~ 3100 ft/sec. It appears that the high impact velocity melted a hole through the steel. I've shot the steel gongs with everything from 22 rimfires to 416 Rigby using all the major cup and core bullets plus most of the premium's. The 180 Sierra's are the only one that has left a hole.

Velocity is the number one factor for a hunting bullet. You can drive a hot dog through a steel plate if its moving fast enough - pure physics you don't want me to explain.

Sectional density is just as important in steel as it is in flesh and bone. MD tests have shown that equal SD's penetrate equally, regardless of caliber.

Hardened inserts in a bullet have effect of keeping the momentum forces linear as opposed to deflected. A soft bullet needs to go faster than a hardened one to penetrate equally.

Caliber by itself inhibits penetration. It is easier to push a needle through something than a 1" punch. A 308 of less SD than a the 22 needs to go faster (relatively) to penetrate equally. A 22 with less SD than the 308 needs to go faster than like SD bullets to be equal.

A hardened target deflects forces from a soft bullet. This deflection can be overcome with "enough" velocity.

Making the assumption that penetration is proportional to stress (force divided by area of contact) and providing bullets are of more or less similar shape and construction, it turns out that penetration is proportional to the square of bullet velocity.

My experience with shooting steel is limited, but the armor plate I have doesn't even have a ding from 140BT's in a 7mmRM when shooting it at 150 yards. Knocks the paint off, but you can't feel any change in the smoothness of the surface. Lots of fun. I have not shot it with any X bullets yet and am curious to see how they treat the steel.

I do remember G&A having an article back in the 90's about the magic of 4,000fps. They showed a picture of a steel plate shot with a 25acp bullet fired from a 257wby; that thing cratered the steel when it hit at something like 4,300fps.

I'll preface this with a warning to all would be experimentors. When I was much younger, we decided to test steel penetration with a newly acquired 6.5x55 using 156gr. FMJ ball. We shot some hardened plate, (maybe grader blade?) at about 30'. The bullet or a fragment thereof, came back and hit my cohort, who was about 2' from my right, in the left elbow, ripping a fair chunk out of his heavy cotton duck parka. Stopped that nonsense right there!
Years later, we got hold of a flywheel from a skidder motor. IIRC, it was about 12"-14" dia. by 2" thick and quite heavy. We stood it on a stump about 50yds away and shot it with the following:
1. .220 Swift, 50gr. Speer with a hot load of 4064. The bullet penetrated 3/8"-1/2", but just tipped the flywheel over, almost gently.
2. .30-06, 173gr. Lake City Match with WW760, doing about 2850fps. This penetrated about 1/4" of the flywheel, but slapped it down with considerable authority.
3. .338 Win Mag, 275gr. Speer at about 2500fps. This penetrated only 1/8" or so, more like a dent, but it caused the flywheel to go spinning off the stump, landing 6'-8' away.
It seems to me that steel penetration has little to do with bullet performance on game, but as I'll freely admit, I'm still learning. We also shot some trees to test bullet penetration too.......

FWIW:

Brennecke hard cast 12 guage shotgun slugs penetrate through the fender of a 1968 Buick, through the power steering unit and well into the outler layer of the engine block at 12 feet.

This result was repeated and confirmed on a 53 ford pickup.

Don't ask. . . .

BMT

I remember reading about bullets punching through steel plate years ago, and it was the same thing, velocity counts. One thing the military has to consider that most hobbyists don't, is whats left of the bullet after it penetrates the armor. 4,000 fps varmint bullets may punch holes in armor, but they might not be good for much after they make it through.

If you want to see what AP bullets are really good for, try shooting sandstone blocks, but thats a different matter alltogether.

FWIW:

Winchester 12 gauge foster slugs will crack an engine block but just leave a lead smear on the surface. They also land with a thud somewhere behind you.

Tim

BMT...

I dunno much about hunting bullets versus steel, not sure there is much to know in any case. There's steel and then there's Steel. Not all created alike and I've yet to see a critter hide behind any of it. Armor plate is a different animal and stopping small arms AP has been commonplace for a long time. The ability to resist the penetration of metals or ceramic plate armor pretty much fades with the .50 BMG AP or larger rounds. Projectile construction is quite important. 5.56mm or 7.62mm caliber cannot be a serious contender for such purposes.

Those who don't think a 5.56 will swiss cheese- as in the vaunted complete pass through, a car or pick up are really deluded. the SS109 ammo penetrates as deep as M2 ball in -06 or standard 7.62 ball does at 100 yards, the 5.56 does lose depth faster than the .30's. Even 9mm will penetrate car doors, a .45ACP 2 of them for sure, the issue with windshields is the slant, the more slant the greater the effective thickness is.

My back stop is 2.0" boiler plate and even .50 BMG ball does NOT penetrate it, nor the brass 650 and 700 grainers. .270 WSM 140 TSX's and .257 Bob 100 TSX's actually leave deeper craters than military ball ammo does.

Having worked on a shooting range for a while and having some sample hardened plates myself, I have noticed a few things

Velocity seems to be the biggest single factor.
Bullet construction DOES has some effect not talking green tips here either]
The type of steel makes all the difference in the world. AR plate is a different animal than 1016 mild steel!!!

I had a 3/8" hardened plate that we were testing stuff on. My 7mm-08 would penetrate it as long as I was under 75 yds. I was using 110 TNTs [the only bullet I could get to penetrate it out of that rifle]

My 300 WBY would penetrate it at 350 yds with a 180 grain Fail safe. A 6.5x284 made a nice little hole at the same distance with a 129 Horny, but only a dent with a 140. Go figure??

17 Rem 25 gr HPs are "better" than 500 + gr cast bullets in 45-70!

I had a 12 inch disc of 1 inch mild steel, which we thought might be fun to shoot from 25 yds with the old 06. My 165 gr ballistic tips at 2800 fps MV were only leaving 3/16 inch craters on the surface.

I also had some military 30-06 AP rounds. The penetrator went to a depth of 7/8 inch and left a pimple on the back side of the one inch plate.

We got smart and found more enlightened pursuits when we realized the noises we were hearing behind us in the blackberry bushes and on the aluminum side of a trailer house was splash back.

I had a friend who set up a private range on his property.The range was 100 yds.Behind the targets were two large steel construction plates of the type used to cover excavation in roadways in order to allow traffic to pass over without refilling the excavations.The plates were leaning over the targets in a manner that would deflect all bullets down into the earth.
Literally dozens of different cartridges of all levels of power were fired into this set up over the years.The only time he would notice holes appearing in the steel was after firing fairly hot .243 loads.He and another friend and his wife were big .243 fans and experimented with a number of fairly hot loads over the years.These loads typically were above the maximum listed loads in the manuals and velocities were typically pretty high.These were not typically first shot penetrations but would appear after tight groups had been shot.
They did not observe the same phenomenon when firing various .25,.270 (including Weatherby) 7mm or .30 caliber cartridges,including various magnums.

Interesting thread, I've been practising alot at our range shooting the 200 metre chicken and our 300 metre pig off shooting sticks. I've been shooting my sons 30-06 loaded just under 2800 fps with 165 hornady's and my 300 win mag with 168 TSX at 3200. I was getting frustrated because I kept missing with my gun and hitting with the 06. So I decided to shoot the pig off the bench and I noticed it moving a bit so I walked down, it is riddled with copper stained holes and penetration marks fomr the 06 leadcore bullets.

So it would appear that both velocity and bullet construction matter vs steel plating.

I want to give a simplified explanation why velocity is so important.

Remember the joke, "it's not the fall that hurt, it was the sudden stop". Forces are applied at the point of sudden stop. It's the point that a bullets momentun converts to pure force. A deflected bullet doesn't stop (altogether) so it doesn't hit as hard. Velocity makes it harder for the target to deflect or slow down the bullet.

Theoretically, if a bullet was stopped instantaneously ... in 0 seconds, the force applied to the target is infinite. Look at the example of a yo-yo. I can work it up and down easily without breaking the string. I can also jerk it to a sudden reversal of direction (stop) and snap the string. The forces jump up proportionally.

When a bullet strikes steel, momentum (mass x velocity) is converted to force in pounds. As soon as the applied force reaches the threshold of the steel, the bullet is allowed to pass.

Because a solt steel will dimple sooner, the pocket has the effect of containing the bullet mass. It can't squirt out the sides like what happens on AR plate so it decelerates more - and more momemtum converts. You can say it actually hits harder. AR or the ceramic armor simply are able to deflect the direction of momentum. Steel also has toughness properties, mild steel is not tough, cannot absorb the energy as well.

I said simplified explanation, maybe not. A hard bullet hits steel harder (more force) than a soft one. Hunting bullets hit a soft steel target harder than hard steel. Any bullet hits harder if it's not splattered at right angles or deflected; hits harder as velocity increases and hits harder with higher sectional density.

As far as armor goes. You want hard to deflect or tough (kevlar) to slow the sudden stop. The best armor is a combination of the two.