Velocity versus bullet drop.

[Treeman]

Is there a kind of ratio or formula that predicts bullet drop or less drop per x velocity change. Can one look up for instance that a 30 cal bullet will drop 20 mm at 100m at 3000 fps and if speed is reduced to 2900 fps it will drop 24 mm - something like that ? A reference of drop increase by velocity loss
.

[BBCT]

Hi Tree

As far as I know, there isn't such a table available, main reason being that there are so many variables to consider. eg using a different bullet will give one a completely different outcome due to changes in BC.

I made up my own table along these lines sometime in the past using Nikon Spot-On calculator (but any only online calculator will do the job equally well). I chose the bullet and fixed all other variables then just ran the calculation a few times, each time with different muzzle velocities.

[Treeman]

Hi Tree

As far as I know, there isn't such a table available, main reason being that there are so many variables to consider. eg using a different bullet will give one a completely different outcome due to changes in BC.

I made up my own table along these lines sometime in the past using Nikon Spot-On calculator (but any only online calculator will do the job equally well). I chose the bullet and fixed all other variables then just ran the calculation a few times, each time with different muzzle velocities.

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I do not think you are correct. The bullet shape may affect the velocity which will affect the drop, as per my question, but the bullet shape itself will not effect drop. Therefore a flat or pointed bullet will have the same drop at the same velocity change, only the velocity change will be at different distances from barrel. Each 180 grain bullet will be x lower for each 100 fps speed drop,but that speed drop will be faster or sooner in the flat bullet than the pointed bullet.
...........................Or something like that huh?

[BBCT]

I follow your logic but any bullet of any shape and any weight will drop at the rate (ie time taken to drop from x height to the ground). If you hold a bullet and drop it to the ground at the exact same instant as you fire a bullet horizontally out of a rifle barrel, the 2 bullets will reach the ground at the same time (assuming ground is level all the way to where fired bullet lands)

If you measure drop against time then the bullet shape won't make any difference but if you measure drop against distance, then the bullet drop at a given distance will vary according to bullet shape because a less aerodynamic bullet slows down more quickly.

The only real way to prove what you are asking one way or another is by actually testing it empirically but most of us don't have time or access to suitable equipment to actually do so.

You can however get a pretty good approximation by using one of the online ballistic calculators. Try it and see what results you get. I reckon you will find that within typical hunting distances of, say 200 metres, that bullet shape & weight make very little practical difference.

Just do the calculations.

[janfred]

Above would be true in a vacuum. When air resistance is included, all kinds of complications appear.

Bullet shape and weight distribution changes the gyroscopic inertia. That governs its rate of attitude change with respect to the air stream along the trajectory. A more-stable bullet generates more lift, i.e. slower drop. It is for this reason that the twist rate of the barrel is included in modern ballistic calculations.

[Treeman]

I kinda just want to know what the drop difference would be for each 100 or 200 fps reduction or increase. Ya I could use the QL Target or some other app, just thought there may be some general rule of velocity horizontally over gravity in general.

[janfred]

First you need the time of flight for your interested velocities at a specific distance. This is the difficult part. BC of bullet makes a difference.

Calculate the drop for each time using 1/2*g.t^2. subtract the smaller from the larger.

Provided you don't try to calculate for further than 500m, the error is negligible

[Treeman]

mmmnnnn?