How hand-thrown fragmentation weapons work (or don’t)

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Hello again folks. This week I’m going to talk about hand grenades. I was prompted by watching the movie Sinners, which (although excellent) features one instance of the terrible “biting the pin off the grenade” cliché. Here’s the offending scene, and you can watch more of it here:

I saw this and realised that I’d never deconstructed the tooth-pulling Hollywood myth¹, so here we are, let’s go!

I’ll start off by giving a quick run-down on modern grenades, and how they achieve their lethal effect. Then I’ll discuss the difficulty with some of the technical details and the techniques we see in Hollywood, such as the aforementioned tooth-pulling, the timing of the grenade’s “bang,” and, of course, the idea of “cooking off” a grenade.

As an aside, I was planning to start a new series this week focusing on military world-building, or how to build story elements which are realistic, plausible, or maybe just about possible. Regardless of whether you are writing for the screen or for the page, historical or science fiction, there are some universal military basics which you might want to read up on. Anyway, not this week, but hopefully we’ll kick it off soon. Watch this space, and let me know if there’s anything in particular you’d like to see.

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Grenades are used in offence and defence

Grenades have a long and storied tradition in warfare, going back as far as the 11th century Song Dynasty in China. As gunpowder weapons increased in lethality and battlefield usefulness, there was always (to a greater or lesser extent) a niche for troops who could get in close and personal and hurl nasty bombs at the enemy. This was particularly useful when storming a fortification, since a lobbed bomb can reach an enemy in cover which a musket ball cannot.

Grenadiers tended to be picked from the biggest and strongest, since height, reach, and physical robustness are obviously conducive to this kind of effort. To this day, although grenades have passed into general issue and there is no specific “grenadier” function on the battlefield, the title is retained by elite units:

The modern grenade (more properly: the hand grenade², there are other types³) weighs roughly a pound, is, well, hand-sized, and has a few other identifying features:

• Safety pin to unlock the fly-off lever
• Fly-off lever which starts the internal and infernal countdown to bang
• External embossing or scoring to aid grip (although not always, as you can see with some of the smooth grenades below)

The external “pineapple” pattern found on most grenades started with the Mills Bomb (top right in above collage) of 1915. The scoring is not about producing fragments of a certain size, it’s purely a grip thing.

The modern grenade comes in two broad flavours: offensive and defensive. These are confusing and a bit of a misnomer, as we shall see.

The German DM51 grenade (top left in previous picture) can be used for both: it has a detachable sleeve which is full of pre-formed fragments. You can throw just the inner part and get a blast effect only (offensive), or include the sleeve, get behind some cover and throw a defensive grenade with nasty fragmentation.

Despite my talk of different “flavours,” I should add unambiguously: you should not eat any part of a hand grenade. Let’s talk about this next.

You’re not supposed to eat any part of the grenade

Safety pins are not part of a balanced diet. Worse again, they are going to be absolutely awful on your teeth. A grenade pin requires a good hard “twist and pull” action to remove it, for obvious safety reasons. Pulling out the pin with your teeth is, at best, impossible, and at worst, will pull your teeth out instead.

I guess if you used your molars on the side you might get enough grip and they would be seated firmly. But even if it doesn’t pull your teeth out, it’s going to chip or otherwise damage them. It’s a bit like opening a beer bottle with your teeth: I cringe just thinking about it. Nevertheless, that doesn’t stop our Hollywood heroes (or villains):

I would forgive a certain amount of this if it served a practical purpose, but it doesn’t. Your other hand is normally free when you’re throwing a grenade, since you want to get the best arc for distance. Unless you’re incredibly ambidextrous, your shooting hand and your throwing hand are going to be the same, so the other one won’t be encumbered by a weapon. And even if it is, there’s no reason you can’t spare a finger to pull the pin.

Let’s look at how grenades actually work in the next section.

The clock doesn’t start until it leaves your hand…

The famous pin which I’ve been talking about is only one part of the grenade’s fuzing system. It doesn’t, by itself, do anything to the grenade. Provided you’re holding it properly (not like in the clip from Sinners above), then the countdown timer doesn’t start until the grenade has left your hand and is on its way to the baddies.

Here’s how the sequence goes. You can follow in the diagram below, which is for a Mills Bomb, although most hand grenades follow a similar logic:

1. The firer holds the grenade with the striker lever in the web (inside) of their hand and twists and pulls the pin with the other hand.
2. The firer throws the grenade. As soon as it leaves the hand, there’s nothing holding back the striker lever, which is spring-loaded. It flies off or open.
3. When the lever flies off it releases the striker, which is also spring-loaded. The striker moves down and strikes the percussion cap, creating a small flame and starting the chemical delay fuse.
4. After the designated delay, the flame travels along the fuse to the detonator and ignites it, causing a detonation shockwave.
5. The detonation wave spreads from the detonator into the high explosive filling of the grenade, causing it to detonate.
6. The detonating explosive causes a blast effect and shatters the casing of the grenade into small fragments with high velocity. Newer grenade designs usually have some sort of pre-scored steel wire or balls around the outside of the grenade to act as pre-formed fragmentation.

…and there’s no way you’re “cooking it off”

Between sequences 3 and 4 listed above, while the grenade is in flight, the firer should have the common sense to get behind some cover. Ideally, they will only have exposed their arm for the brief moment it took to lob the grenade.

This is especially true if it’s a defensive grenade, i.e. one which generates fragments and therefore has a greater danger area. One of the curious things about hand grenades, compared to most munitions, is that the danger radius is usually a lot bigger than the feasible throwing range.

I had an army buddy who thought that the answer to this “problem”⁴ was putting a grenade on a string, using the slingshot idea to build up angular momentum and transform this into a long-distance lob. He actually tried this once (with an expended smoke grenade, I hasten to add), and the resulting trajectories were as erratic as you might imagine.

The main problem⁵ with the “grenade on a string” idea was fuzing. How do you ensure that the grenade is safe while you’re twirling it around, but then start the countdown reliably once it leaves your control? I bring this up not to dump on my buddy (although he deserved our ridicule. As Miss Hoover famously said: “The children are right to laugh.”), but to dump on another concept we see in movies and video games: “cooking” grenades.

Coming back to the Sinners clip above, which started this whole rant, you’ll notice that he pulls the pin and lets the lever fly off while the grenade is still in his hand:

This is “cooking,” or deliberately letting the grenade fuze time down by a few seconds before throwing it. There’s a surprising amount of dangerous misinformation online about this, including some WikiHow, Quora, and Reddit posts which talk about it like it’s a real thing. I can only speak from my own military experience, and it’s absolutely not a thing.

I think it comes from video games, where I recall many successful kills like this one below with cooked grenades. The guy gets a lot of pleasure from his kill! Like many aspects of Call of Duty, though, it’s not something you’d ever do in real life.

Holding a struck grenade in your mitt for a second or two requires a lot of faith in various things which a soldier would not normally have faith in:

• Their ability to accurately count seconds when under adrenalin-soaked combat conditions
• Knowledge and recall of the exact countdown time from training, even though this is normally given in a range to indicate some inherent uncertainty
• Trust in the quality control processes of the manufacturer (who was probably the lowest bidder for the product)

When it comes to grenades, you hold it properly, you pull the pin with your other hand, you throw it promptly, you watch to see where it lands⁶, and then you GTFO of harm’s way.

Conclusion: The rule of cool

Grenades are, at least from a Hollywood point of view, one of the cooler weapons out there. They rely on the hero’s physical qualities like dexterity and strength, as well as the smarts to time the throw just right. They also allow the camera to get a good thirst shot of a muscle-bound hero.

What self-respecting action hero would worry about their dental insurance in a situation like that? And what kind of nervous Nellie can’t do a simple count to three before throwing the grenade? The rule of cool means that the infractions are automatically forgiven when the outcome results in cinematic glory.

There’s a parallel here with the grenadiers of old, in their tall hats and bright uniforms, throwing flaming balls of explosive onto ramparts. They were the action heroes of their day. For all the advances we’ve made in modern weapons, and all the science fiction weapons of the future, nothing beats throwing a ball of explosive death straight at the baddie, demonstrating your own non-explosive balls in the process.

That’s it for this week, folks. Thanks for reading and please remember, if you haven’t already, to subscribe using the link below. Please also share this article with a friend. See you next week.

Featured Image: Michael B. Jordan Destroys The KKK Scene | SINNERS (2025) Movie CLIP HD, via YouTube

1. Although plenty of others have. ↩︎
2. Or “Grenade, Hand,” in the ridiculous but slightly endearing way the military writes backward to designate things. ↩︎
3. Rifle-fired grenades and projected grenades (i.e. what you fire from a grenade launcher). Within the class of “Grenade, Hand,” you also have a bunch of pyrotechnic grenades which emit screening or signalling smoke, and flashbang grenades which are used to disorient during breaching operations. And that’s without getting into the huge array of practice and drill grenades. Today I’m just focusing on high explosive hand grenades. Luckily, that’s mostly what Hollywood focuses on too. ↩︎
4. It’s really not a problem. It’s why you get behind cover when you throw the thing. ↩︎
5. I’m being a bit generous here. There were many problems with this idea. ↩︎
6. In case it doesn’t detonate, so you know where to avoid walking and can tell the person who’s job it is to destroy such “blind” grenades. ↩︎