How fast do bullets slow down in level flight?

Somewhat of a thought experiment:

I hold some firearm out with a muzzle velocity of, oh, let’s say 1000-2000 fps. Assuming the firearm is perfectly level and about 5 feet off the ground the bullet will hit the ground in about 0.56 seconds.

Once it stops accelerating after it exits the barrel, it starts slowing down as the result of drag, but how much at the time it hits the ground a half-second or so later? I suppose that temperature would have some bearing on the slowdown, too.

It depends on the ballistic coefficient of the bullet-how aerodynamic it is. A more streamlined bullet slows less.

Velocity also matters, air resistance quadruples when you double velocity.

Ballistic charts.

This is a complicated question with lots of variables. Most rifles aren’t sighted in to shoot flat and start dropping straight out of the barrel. They are usually sighted in for some particular distance farther out and the ballistic curve will show that the bullet rises and then drops to hit where it should at the desired point of impact. The bullet did not gain any lift but it was fired at a slight upward arc.

You can play around with a ballistics calculator to answer this question. It will at least show you the some of the variables you need to take into account. I put in some rough numbers for a .30 caliber rifle bullet fired at 2700 feet per second perfectly flat which is similar to the very popular 30.06 cartridge. It hit the ground about 450 yards out and was still going about 1600 feet per second.

In general terms, spitzer-pointed, boat-tailed bullet bullets that are long for caliber will retain velocity better than shorter,flat-based, round-nosed bullets. Cartridges like the 6.5 Creedmoor take advantage of these factors. Basically, a cartridge like the 6.5 Creedmoor can be loaded to lower pressures and use less powder because the higher retained velocity at range allows a lower muzzle velocity. This is often what shooters mean when they describe a cartridge as “flat shooting.”