Bullet weight affect on 100 yard zero?

[Ruskie74]

Hi All,

I hope this isn't too silly of a question, but how much does the weight of the projectile really affect 100 yard zero? For example, if your .308 is zeroed using 168 grains bullets, will 175 grain rounds impact at essentially the same 100 yard zero?

I do realize that of course the heavier bullets drop faster, so 200 yards and out one would need different DOPE numbers, but how much of a difference does this really make at 100 yards? I've tried this out with 5.56 (55 to 69 grains, 6.5 130 vs 140 grains, .308 168 and 175 grains, and even 300 WM 190 to 220 grains, and while I do see lateral movement between the different bullet weights, I'm not really seeing any significant difference in vertical impacts - they all seem to be within .5 inches of each other vertically.

I ran some ballistics software for 338 LM in 250 and 300 grains, and the difference of drop at 100 yards was measured in the thousandths of an inch:

100

0.0076

-0.0015

That seams rather inconsequential to me, and that is with a 50 grain difference. What say all of you?

 

[Greg Langelius *]

Drop is solely a matter of time to target. 32ft per second squared. Bullets are always falling in flight. compared to the straight line extending out of the barrel, extending the bore axis.

A heavier bullet might depart slower; increasing TOF, and drop along with it.

At 100yd, that difference is usually very small.

Note, a heavier bullet will often have a higher ballistic coefficient (BC), reducing drag, decreasing TOF; and thereby also reducing drop (and wind drift), thus striking higher, rather than lower, at extended distances.

A lot that seems intuitive, ain't.

When we're new to ballistics, it's easy to get tangled up in the numbers. We tend tothink in terms of absolutes. Absolutes are seldom so absolute, because they are also combined with human inaccuracies. When an absolute dictates a deviation of .5 inches at 200yd, and we're unable to maintain our aim within 2 inches at that distance, the absolute loses the argument.

Greg

 

[tna9001]

Vertical dispersion is just half of it. Different shaped (weight) bullets will impact differently and it has nothing to do with weight but the shape of the projectile sent through a given barrel.

 

[spife7980]

I hope this isn't too silly of a question, but how much does the weight of the projectile really affect 100 yard zero? For example, if your .308 is zeroed using 168 grains bullets, will 175 grain rounds impact at essentially the same 100 yard zero?

That would be nice but unfortunately its more of a random dice roll. It could hit higher or lower, or left or right, just depends on that particular barrels relation ship with the particular bullets at that particular point and space in time. Some track like you would intuit, others do the opposite.


Each one of these is a mode of vibration, they are all happening every time at once, bullet weight is just one of many many factors. Shooting it is the only way to actually tell.
https://www.varmintal.com/amode.htm

A bigger better barrel will deflect less over all so hopefully the different bullets will impact closer to one another but its just no guarantee. My old 30-06 barrel would put the 150 partition and the 150 accubond close enough for deer hunting, like one group just to either side of the dot but the 150 ballistic tip was 3" out just to be a pain in my butt and there was nothing to be done about it.

 

[Steel head]

That would be nice but unfortunately its more of a random dice roll. It could hit higher or lower, or left or right, just depends on that particular barrels relation ship with the particular bullets at that particular point and space in time. Some track like you would intuit, others do the opposite.


Each one of these is a mode of vibration, they are all happening every time at once, bullet weight is just one of many many factors. Shooting it is the only way to actually tell.
https://www.varmintal.com/amode.htm

Looks a lot like Japanese cartoon porn.

 

[spife7980]

Looks a lot like Japanese cartoon porn.

 

[Steel head]

 

[Ruskie74]

thanks for the great explanations. Real world testing proved you all correct. I'll have to find a favorite load for each rifle and stick to it,

 

[FLguy55]

My thought has always been that the difference seen at 100 has more to do with the difference in fps than the bullet weight itself being impacted by gravity. Down range being a different story of course.

 

[spife7980]

My thought has always been that the difference seen at 100 has more to do with the difference in fps than the bullet weight itself being impacted by gravity. Down range being a different story of course.

If you shoot an OCW you’ll see that as you increase the charge weight the point of impact moves up down left right and all around.