Flatness of trajectory


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Dumbo
June 9, 2003, 03:12 AM
I've posed this question on other boards and received mixed answers.

Which is a more accurate gauge as to whether or not a cartridge can be referred to as "flat shooting" at a certain distance from the target, how much bullet drop it experiences before reaching the target if the rifle is set for a point-blank zero or the level of sensitivity to error in distance approximation the cartridge displays at that range?

I personally believe that the primary advantage of a “flat shooting” cartridge is not a matter of ergonomics for most shooters and that how far someone has to turn their scope is not the main issue.

Let's take a look at a situation regarding the .223 Remington and the .308 Winchester. A .223 Remington 55 grain Sierra BTHPMK with a muzzle velocity of 3,240 feet per second and a Ballistic Coefficient of .225 only experiences 48.45 inches of bullet drop at 500 yards with a “zero” of 200 yards and a .308 Winchester 155 grain Sierra BTHPMK bullet with a muzzle velocity of 2,650 feet per second and a Ballistic Coefficient of .447 experiences 51.85 inches of bullet drop at 500 yards with a 200 yard "zero”.

Let’s take a look at the implications of this.

Two competitive shooters, one using the previously mentioned .223 Remington load and the other using the previously mentioned .308 Winchester load, are confronted with targets 500 yards away.

They both neglect to make any adjustment to the elevation settings on their scopes and simply use a 200 yard center of mass aim. The shooter using the .223 Remington will only shoot 48.45 inches low and the shooter using the.308 Winchester will shoot 51.85 inches low.

However, let's imagine that both shooters attempt to estimate the distance to the target and adjust the elevlation on their scopes.

Let’s assume both shooters estimate the distance to be 495 yards. The person shooting the .233 Remington will be shooting 1.15 inches low and the person shooting the .308 Winchester will be shooting 1.08 inches low.

How about if they both estimate the distance to the target to be 350 yards? The person shooting the .223 Remington will be shooting 29.41 inches low and the person shooting the .308 Winchester will be 28.71 inches low.

Basically, the .308 Winchester will experience less bullet drop unless both shooters estimate the distance to be less than 325 yards. Also, the shooter using the .308 Winchester can estimate the distance as low as 453 yards or as high as 544 yards and still stay within a 10 inch “kill zone” while the shooter using the “flatter shooting” .223 Remington must guess somewhere between 455 and 539 yards in order to stay within that same 10 inch “kill zone”.

On one hand, the .223 Remington only takes .686 seconds to travel to the target and the .308 Winchester takes .697 seconds.

On the other hand, the bullet does not start to fall until its vertical velocity becomes equal to zero. With a 495 yard sighting, that point is 280 yards for the .223 Remington and 270 yards for the .308 Winchester. The thing is, the .223 Remington takes .371 seconds to travel from 280 yards (the highest point in its trajectory) to 500 yards (the distance to the target), whereas the .308 Winchester takes only .357 seconds to travel from 270 yards (the highest point in its trajectory) to 500 yards (the distance to the target). In other words, the trajectory of the .308 Winchester is actually flatter within the relevant distances where bullet drop occurs.

However, the shooter using the .223 Remington will suffer less strain on his wrist as a result of the fact that he will turn the scope less.

The question I pose to you is which load is to be regarded as “flatter shooting” at 500 yards? Personally, I would choose the decreased sensitivity to distance approximation errors that are likely to occur over the issue of ergonomics. What do you guys think?

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Jon Coppenbarger
June 9, 2003, 08:21 AM
you leave out to much info.

I'am assuming that you ar shooing those rifle threw a rifle with very slow twist.
a 1/13or 1/14 twist 308 will shoot those type's of weight's out to 1,000 yards with a great accurracy .
but the .223 is at a very big disadvantage at 500 with that type of load as it is having to be pushed at such a great velocity out of a rifle and twist better suited with a rifle with a slower twist and heavier bullit.
the .223 will stabilize a bullet of 90 grains very well out to 1,000 but the twist will ned tobe in the 1in 6.5 range to get there.

also out of the 308 with that weight you would be better off chosing a palma bullet as with that other bullet you mentioned is not the normal round you would use for that range unless it is a palma or long range rifle with a very fast twist rate.

if you give us the rifle and twist rate and your barrel length someone might be able to get you alot closer to what you seek.

you also fail to mention what kind of competition you are interested in doing this in.
picking ballistics off of a computer program and not giving full info or intentions is not the best way to pickout what might be best.
if you ar looking for the answer to your particular answer you already gave it in your formula.

Grump
June 10, 2003, 04:07 PM
Seems to me that flat trajectories from high velocity are truly an advantage for only the first 300 yards when shooting soda-can-size targets.

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