Would a 12 Gauge Slug Knock You Over While Wearing Armor?

DMW1116 said:

Why is there thousands of foot pounds of muzzle energy but only dozens foot pounds of free recoil energy?

Click to expand...

Force = (mass)(acceleration)
acceleration = (change in velocity)/(time)
Velocity = (displacement)/(time)

Limiting factors: The resistance acting to prevent one object from moving vs. resistance acting the other.

In this case the mass off the shotgun is more of a detriment to acceleration so the force is less.

The same me amount of energy that recoiled the shotgun is acting on the considerably lighter mass slug, causing a greater amount of acceleration. When the acceleration increases so significantly it translates into more force.

The “equal and opposite” part in this case means there is the same amount of energy acting to push the slug forward as there to push the shotgun backwards, but other factors such as mass and resistance translate that equal amount of energy into doff levels of force.

Well, to be picky, the net momentum for the guy that shot himself is zero so he should be okay from a momentum standpoint.

Energy has to be conserved too. Where did the difference in energy go?

It might knock an unprepared person off balance.

LookAtYou said:

If wearing body armor that could effectively stop a 12 Gauge Slug from penetrating, would the ridiculous momentum from the slug Knock the wearer over, if not send them flying back? A 1.25 Oz Slug @ 1551 FPS delivers 2920 Ft/Lbs of kinetic energy and 121 Ft/Lbs of momentum. What would happen?

Click to expand...

Depends.

Ever shot a 12 gauge with magnum rounds? Either 3" magnum or 3 1/2" super magnums? You need to snug that butt into your shoulder and lean into it. The same amount of force felt at your shoulder would be felt upon impact with the armor. You can easily bruise your shoulders, especially if you insist on shooting a lot of them.

If you're not already braced or otherwise unbalanced in your stance, yes it could topple you or otherwise knock you for a loop. "Stagger" would probably be a good word to use. But that's because you're a biological, bipedal machine. That means your balance, especially in motion, is less stable than, say, an inanimate object like an equivalent mass in the form of a block. You are also more flexible.

Send you flying back? No.

It's not energy which pushes something over. It's force. Force is equal to mass times acceleration. Therefore, acceleration is equal to force divided by mass.

For a given impact force, the larger the target compared to the slug, the less it will accelerate.

SO...let's look at it one way:

Assume the mass of the slug is one ounce. A 180 pound person after being shot has a mass of 2,881 ounces. (180 pounds times 16 ounces per pound, plus the slug).

The force the bullet delivers (mass times acceleration) has to be calculated from momentum. How the bullet decelerates determines its force. And this depends on the slug's terminal performance.

Acceleration would be calculated by the change slug in velocity upon impact divided by the change in time. You need to use the inelastic equation for this, since the slug does not pass through the person.

These calculations require you to make some assumptions with respect to the change in velocity of the slug and the time it takes for that to happen. And that's difficult.


BUT...using momentum equations straight up, you can get a better feel. Momentum is mass times velocity.

Momentum is always conserved.

So momentum of the bullet is the mass of the bullet times the velocity of the bullet.

Momentum of the target is the (mass of the person + mass of the bullet) times the velocity the combined masses.

If you look at the relative difference in mass (1 ounce vs 2881 ounces), you can see that whatever the initial velocity of the slug is will be radically reduced for the combined mass of the person and the slug together.

DMW1116 said:

Energy has to be conserved too. Where did the difference in energy go?

Click to expand...

Some was bled through air resistance most was transferred from the slug into the armor plate (which is partly why the slug doesn’t penetrate), a lot was transferred into the tissue behind the plate. Enough to break ribs, perhaps bruise organs etc but not enough to knock someone down who wasn’t precariously perched to begin with.

RetiredUSNChief said:

Depends.

Ever shot a 12 gauge with magnum rounds? Either 3" magnum or 3 1/2" super magnums? You need to snug that butt into your shoulder and lean into it. The same amount of force felt at your shoulder would be felt upon impact with the armor. You can easily bruise your shoulders, especially if you insist on shooting a lot of them.

If you're not already braced or otherwise unbalance in your stance, yes it could topple you otherwise knock you for a loop. "Stagger" would probably be a good word to use. But that's because you're a biological, bipedal machine. That means your balance, especially in motion, is less stable than, say, an inanimate object like an equivalent mass in the form of a block. You are also more flexible.

Send you flying back? No.

It's not energy which pushes something over. It's force. Force is equal to mass times acceleration. Therefore, acceleration is equal to force divided by mass.

For a given impact force, the larger the target compared to the slug, the less it will accelerate.

SO...let's look at it one way:

Assume the mass of the slug is one ounce. A 180 pound person after being shot has a mass of 2,880 ounces. (180 pounds times 16 ounces per pound, plus the slug).

The force the bullet delivers (mass times acceleration) has to be calculated from momentum. How the bullet decelerates determines its force. And this depends on the slug's terminal performance.

Acceleration would be calculated by the change slug velocity upon impact divided by the change in time. You need to use the inelastic equation for this, since the slug does not pass through the person.

These calculations require you to make some assumptions with respect to the change in velocity of the slug and the time it takes for that to happen. And that's difficult.


BUT...using momentum equations straight up, you can get a better feel. Momentum is mass times velocity.

Momentum is always conserved.

So momentum of the bullet is the mass of the bullet times the velocity of the bullet.

Momentum of the target is the (mass of the person + mass of the bullet) times the velocity the combined masses.

If you look at the relative difference in mass (1 ounce vs 2881 ounces), you can see that whatever the initial velocity of the slug is will be radically reduced for the combined mass of the person and the slug together.

Click to expand...

Way better explanation than mine.

RetiredUSNChief said:

Depends.

Ever shot a 12 gauge with magnum rounds? Either 3" magnum or 3 1/2" super magnums? You need to snug that butt into your shoulder and lean into it. The same amount of force felt at your shoulder would be felt upon impact with the armor. You can easily bruise your shoulders, especially if you insist on shooting a lot of them.

Click to expand...

That holds true even for light target loads; called Newtonian physics. And if your gun doesn't fit, even a 410 can leave a mark, let alone some bruiser of a 12

I remember duck hunting once and I was standing in one spot waiting on a parter to catch up, my feet sunk into the mud probable 14 maybe 16 inches, my feet were locked. Something flew by and I took a quick shot despite the terrible stance, and I very nearly bent at the knees and went down, had it been a slug I have no doubt I’d have been in the water. Was hunting with a 12ga Beretta 391 if memory serves.

Don’t get me wrong I don’t even think a 10ga would physically lift a man from the ground, but I fully believe it will put him on it, regardless of body armor. The shock (maybe trauma is a better word) of a impact like that would be massive.

Then again I could be wrong.

I'd be worried about the massive internal trauma instead of whether I was still on my feet, were I hit with a slug while wearing body armor.





Paul shoots a 3a with a bottle of pop behind it, with logs to fill out the vest starting at 2:08. The shot is at 3:00. That bottle of punch is your lung. Watch what the slug does to a cinder block in a 3a vest at 3:27. .

LookAtYou said:

Thanks. Yea, no human can literally punch as hard as certain 12 ga slugs, even pro heavyweight boxers. With 2920 Ft/Lbs of force from a slug, (compared to say a .40 with 474 Ft/Lbs or a friggin .556 with 1236 Ft/Lbs, which is still a lot in it's own right) just the brute force by itself is a weapon. It's up there with 300 Win Mag.

Click to expand...

It is still Newton physics with equal and opposite reactions

The one between free recoil and muzzle energy.

I know a gentleman who was knocked over when shooting a SxS 12g. The rest of the story:
- duck hunting
- buddy next to him fired at the same time
-...while seated and both turned sideways, in a canoe
- splash!

LookAtYou said:

Thanks. Have you seen this video?

Click to expand...

I hadn't; thanks for posting it! He's about 90 miles north of me.

No but my money is on you double over and kiss asphalt anyway. I can’t imagine the gut/chest punch from a 12 gauge slug. Makes me want to puke just thinking about it. It’s gonna leave an ouchy for sure and could very well kill you.

Weebles wobble but they won't fall down