What does Flat Shooting/Bullet Drop Mean?

| June 24, 2011 | 8 Comments

Regular commenter ScottW asked the question of: What exactly is a flat shooting cartridge or load?

“A Flat Shooting” cartridge or load refers to a cartridge or particular load’s flat trajectory over a given distance. What that means is over a given distance, a flat shooting load will have less drop (bullet falling towards the ground) than a load that is not flat shooting.

The faster moving a projectile is, the flatter it will shoot. For example: a .223 40gn projectile at 3542fps or so will shoot flatter than a 60gn at 3060fps out to around 400 yards.

Major causes for this are #1 time of flight; the time gravity has to interact with the projectile while it is in the air (higher muzzle velocity the better) and #2 the projectile’s ballistic coefficient [BC] (a measure of the bullets drag). There are probably more minor factors but these are the two important ones.

For example:

In a .223 Remington, a 40gn Vmax projectile shot at a velocity of 3542 feet per second sighted in at 150yds will take 0.32 of a second to travel to 300yds. As it is sighted in to be dead on at 150yds the amount the projectile has dropped at 300yds is 8.59 inches or 214mm.

In contrast going up to a 60gn Vmax projectile with a muzzle velocity of 3060fps will take 0.36 seconds to travel 300yds. Whilst it will be dead on at 150yds it will have dropped 10.79 inches or 269mm at 300yds.

So the 40gn projectile with poorer BC but higher velocity (quicker time of flight) in this example drops 2 inches less than the 60gn which has a longer time of flight but better BC. This show’s that time of flight is a more important factor when comparing two different projectile weights from the same cartridge.

When trying to compare whether a particular cartridge shoots flatter than another an easy way to do it is to find load information for the exact same projectile:

A 22-250Rem shooting a 40gn Vmax at 4000fps will of course shoot flatter than the same projectile being fired out of a .223 at 3542fps. Even a 60gn Vmax out of a 22-250 will shoot flatter than the 40gn load from a 223.

When all things are equal Ballistic Coefficient wins.

Two projectiles of the same weight but different ballistic coefficients are fired at the same muzzle velocity as one another. The one with the higher BC will always shoot flatter. This is due to the projectile with the lower BC being less aerodynamic which leads to it slowing down quicker than the projectile that is the same weight but has a higher BC. An example of this would be a flat nosed projectile (low BC) vs a plastic tipped projectile (high BC).

Now don’t confuse trajectory with wind drift, as BC is the major factor in this scenario and just because a load is the flattest shooting it does not mean that it is the best load to use.

Hopefully I haven’t made this over-complicated.

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Category: Hunting Rifles

Comments (8)

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  1. ScottW says:

    Thanks for the explanation Keith. I’m playing with the Winchester ballistics calculator app on my iPhone, which is helping me to better understand this.

    I have a question though: How is BC determined, theoretical or practical? I assume a BC of 1 would be the mythical ‘bullet in a vacuum’ perfection.

  2. Keith Drain says:

    I pondered writing an article on BC but I am scared to as I don’t understand it enough.
    There are different models you can use etc.
    I do know you need the velocity at the muzzle and the velocity at 100yds then you do a calculation to work out the BC. There is a free ballistics program called Point Blank that will do it for you if you know those two variables.

    http://bulletin.accurateshooter.com/2008/02/free-point-blank-ballistics-software/

  3. Adam says:

    For drop and wind drift, it is all about velocity. Drop is a constant, the force exerted by gravity does not vary (in this context) and the faster a bullet gets to the target, the less it will drop.

    Wind drift is not a constant. Drift is related to the amount of force exerted by wind. Like drop, within 300m the short time of flight does not allow wind to exert much force.

    This all changes as bullets start to slow down. At 300m, a bullet is often doing ust over half the velocity it left the muzzle with. It now takes nearly twice as long to cover that 300 to 400 distance as it did to cover the 0 to 100 distance. NOW the slippery nature of the bullet starts to really pay off as it will retain velocity better than one less slippery.

    The advice I often give is that if you are shooting within 300m, don’t get wrapped up with the best BC, but past 400m BC is becoming more important.

    If you look at what competition shooters load this guidance is bourne out.
    Benchresters usually shoot at less than 300m. For the most part they run flat based bullets, mostly in a sub 70gn 6mm factor. This is not a high BC bullet.
    F Class shooters shoot out to 1000m. For F unlimited the heavy for calibre high BC bullets are the favourite. Even for F Standard 223s shooting 70gn+ high BC bullets is the norm.

  4. Bozo says:

    “The advice I often give is that if you are shooting within 300m, don’t get wrapped up with the best BC, but past 400m BC is becoming more important.” By Adam

    Best comment in this whole thread! Find a load that your guns shoots accurately and use it.

    Another rambling nonsense article by Keith.. Time to go out and shoot more and stop worrying about what it says on paper buddy!

  5. Keith Drain says:

    Grow some balls and use a real name bozo.

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