After Heather Heyer was murdered via car attack in August 2017 I did a lot of research and discussion with people about the possibility of having armed patrols on the perimeter of protests to stop vehicular attacks.

This research seems relevant now.

Stopping a moving car at high speed is difficult and dangerous. The vehicle has momentum and will continue to move even after having lost power or direction. However, preventing the driver/vehicle from accelerating or steering can prevent or reduce casualties in an attack.

We have to confront the question: in this situation, do you shoot the driver, or do you shoot the engine? Shooting the driver is a much more difficult proposition, legally and ethically. There is a possibility that you might shoot someone who is NOT intentionally ramming.

If you shoot their vehicle instead, and they successfully argue that it was not an intentional ramming attack, you will still be on the hook but for much lesser charges than if you had murdered or attempted to murder them.

Therefore, I will discuss shooting the vehicle first.

I spent a lot of time looking into what it would take to kill a car's engine. I'll summarize what I found.

TLDR: It is possible to kill a car's engine with a firearm, but only with specific guns and ammo, and even then it is unreliable.

To stop a car engine and prevent the vehicle from accelerating you need to hit very specific components. You need to destroy the engine block, or the drive shaft, or kill power to the spark plugs. Alternatively, destroying the steering column can lock the car into its course.

Poking holes in the radiator or damaging the battery will kill the car eventually; but you need to stop it now. Since the alternator and electrical components are small targets, the only realistic thing to try to hit is the engine block. Specifically you need to pierce a cylinder

The vast majority of firearms cannot pierce an engine block. Lead projectiles from any firearm will tend to splatter on the steel engine housing; you'll be lucky to cause a dent. 9mm, 12ga slugs, .223, .308, .50 BMG -- doesn't matter, if it's a lead projectile it won't work.

To pierce an engine block you need a steel or ceramic projectile, which means armor piercing, and you need it to be of sufficient power as well. In my research, the bare minimum sufficient to reliably pierce an engine block is an M2 AP projectile

M2 AP "black tip" is a projectile that was developed for the US .30-06 cartridge in the 1930s for use in machine guns, though it saw use in Springfield and Garand rifles as well. It's a 162gr hardened steel core projectile going 2800fps out of the original .30-06 M2 AP cartridge.

The M2 AP projectiles can also be loaded into .308 / 7.62x51mm cartridges; however, the ATF considers .308 to be a "handgun" round, and Federal Law prohibits armor piercing handgun ammunition. This is a big gray area, so consult with a lawyer, at your own risk, etc

M2 AP is widely available and legal in *most* jurisdictions, though expensive, in both loaded .30-06 cartridges, and loose projectiles. The M1 Garand is a very common .30-06 semi-auto rifle, and there are a plethora of semi-auto .308 guns. This is a very viable load to carry.

There are some other options -- various armor piercing projectiles in other calibers, steel shotgun slugs, and of course .50 BMG AP. But these are all far more expensive, less available, and more conspicuous than a .30-06 or .308. The M2 AP is the most viable option.

That said, it's imperfect. You're shooting at an engine block that you can't see, that takes up maybe 25-40% of the volume of the engine compartment. Most of your shots are going to miss or glance off. You need to dump rounds into the engine compartment until it stops.

And again, this is marginal. In Syria, the SDF had to deal with ISIL suicide car bombers ramming their checkpoints. They initially used .30 machine guns and rifles firing 7.62x54r armor piercing incendiary (API) rounds. Still, some car bombers would make it through.

Eventually ISIL started adding armor to the engine compartment and passenger cabin, and the SDF was forced to upgrade to 14.5x114mm and 20mm anti-materiel rifles firing API or high explosive rounds.

So again, TLDR: It is possible to kill a car's engine with a firearm, but only with specific guns and ammo, and even then it is unreliable.

That finally brings us back to targeting the driver. This is ironically a much simpler problem.

Use a rifle or a shotgun slug and aim for the upper chest.

Have money for a good lawyer.

Pray that you're not making a mistake.

Don't miss.

RE: targeting/damaging tires. Cars can still drive at lethal speed with flat tires. It's bad for the wheels and axles, but if they're intentionally wrecking their car into someone anyway I doubt the attacker cares.