Curious about Downrange Ballistics

[WBH]

In theory, shouldn't the same bullet whether launched from any barrel of the same twist and length at the same velocity have the exact same ballistics.

For Example:
A 220gr cast bullet of the same alloy, BC etc shot from a 300AAC, 7.62x39, .308 or 30-06 at 1050fps from a barrel of the same twist and length should essentially be the same "gun".

I must be getting cabin fever. and it's only mid December:(

[dangitgriff]

There are more variables to consider.
Internal ballistics variances: case dimensions, primers, powder charge, chamber/barrel temperature;
External ballistics variances: temperature, humidity, wind speed/direction.
Hope this helps! [emoji106][emoji1783]

[Rcmaveric]

Yes and No. Yes, your trajectories will be very similar. I think you are just looking at more complex than it really is.

Velocity plays the biggest role in trajectories. In the fractions of a second it takes bullets to travel x amount of distance, most bullets will fall the same amount in that time regardless of weight or BC. At around 150 yards is when I think BC starts effecting things. If you are going around 2000+fps then BC will only help wind deflation out to 200 yards. After 150-200 yards, velocity retention methods (weight or BC) will alter trajectory.

Take two bullets and drop them. Which one hits the ground first? All things fall similarly the first second or two.

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[charlie b]

If the bullet is 'undisturbed', once it leaves the barrel it really does not matter which cartridge or rifle fired it. That's why there are ballistics tables based on bullet and velocity, along with the atmospheric conditions.

PS just to be complete, no bullet is undisturbed in the path through the barrel. Different number of grooves, slightly different bore and groove sizes, roughness in the bore, fouling, chamber dimension slightly off, etc, etc. Any disturbance will affect the flight of the bullet to some degree. How much does it affect it? It depends :)

PPS one other item. No two bullets are exactly the same either. Despite best efforts there will be some difference. You probably could not measure the contribution from this, but, it is there.

[stubshaft]

Theoretically, yes.

[Larry Gibson]

If the bullet is 'undisturbed', once it leaves the barrel it really does not matter which cartridge or rifle fired it. That's why there are ballistics tables based on bullet and velocity, along with the atmospheric conditions.

PS just to be complete, no bullet is undisturbed in the path through the barrel. Different number of grooves, slightly different bore and groove sizes, roughness in the bore, fouling, chamber dimension slightly off, etc, etc. Any disturbance will affect the flight of the bullet to some degree. How much does it affect it? It depends :)

PPS one other item. No two bullets are exactly the same either. Despite best efforts there will be some difference. You probably could not measure the contribution from this, but, it is there.

Basically what Charlie said. To simplify; if it is the same bullet at the same velocity the ballistics [external] will essentially be the same. Length of barrel doesn't matter. As long as the bullet is stable the twist doesn't matter either except at very long ranges with jacketed bullets or unless the RPM Threshold id crossed with cast, then the twist will matter.

[WBH]

stubshaft........Thank You. The simple answer is sometimes the best!
"All else being equal"......I agree!!!

[country gent]

The new lab radar makes testing this proving it a lot easier it gives velocity at several points over a couple hundred yards. A reading at the muzzle and one at 200yds from the same shot plug the numbers into one of the programs on the net and you get the actual bc at that velocity range. They do vary with velocity, as velocity goes up so does BC. Height above sea level also has an effect along with some others. twist really affects spin drift at long ranges more than drop. Another is the bullet must stay stable thru flight

[Wolfer]

I can tell you that my 311041 pushed to 1800 fps kills deer the same whether it come out of my 30-30, 30-40 or 30-06. All three have 10” twist.
This is pretty informal but it works for me.

[Petander]

One bullet , one rifle , loaded to one muzzle velocity with various powders. Same?

No. Different powders even in one rifle have a different POI and accuracy/grouping. SD,ES... I have some experience from 300 WM in particular. The differences show better @ 300 meters and further.

[onelight]

all things being equal......are equal

[charlie b]

One bullet , one rifle , loaded to one muzzle velocity with various powders. Same?

No. Different powders even in one rifle have a different POI and accuracy/grouping. SD,ES... I have some experience from 300 WM in particular. The differences show better @ 300 meters and further.

I would wager that the difference is in the pressure curve and barrel nodes. Even a slight difference can cause the barrel to be at a slightly different angle when the bullet leaves the muzzle. That's why it shows up at longer ranges, because the difference is small.

Again, once it leaves the barrel the drop will be the same based on the muzzle velocity.

ES and SD are not in question. If the velocity is the SAME (0 ES and 0 SD) the bullets will follow the same path.

[Petander]

Okay,when everything is the same,it's the same. :)

When a bullet is coming out the barrel, different powders have different amounts of gases coming out differently. They disturb the bullet differently. Also,the bullet speed is "the same" for a slight theoretical amount of time only. It's either accelerating or slowing down.

Same is same but can it ever be the same,twice? If Earth was flat,would it be flat?

[bmortell]

maybe one of them would be launcher at a higher peak g force and slumps the nose slightly, and changes the bc causing the same bullet at same speed to act differently.

I don't know, you gotta be pretty picky to make the same thing be different

assuming hes not talking about poi or accuracy as ballistics, for calculating ballistics you assume its already sighted in at x distance, and different guns and loads having different accuracy should be obvious

[Petander]

For Example:
A 220gr cast bullet of the same alloy, BC etc shot from a 300AAC, 7.62x39, .308 or 30-06 at 1050fps from a barrel of the same twist and length should essentially be the same "gun".



No. Unless we take the guns out of equation. Then all we have is a theoretical bullet which is "the same".

We are not the first ones,trying to figure this out. :)

[charlie b]

After the bullet leaves the muzzle blast there is no more effect from the rifle on the bullet, NONE. If it is traveling in the same direction at same velocity it will hit at the same point based on the aerodynamics and atmosphere.

The 'traveling in same direction' is the key to the different rifle approach. Barrels are funny that way as they wobble and shake as the bullet travels through them. Even two different bullets with the same powder charge may not leave the barrel going in exactly the same direction, even if they are the same velocity. One of the key aspects of finding the most accurate load in a rifle.

[Larry Gibson]

To simplify; If the same bullet is used at identical MV and the rifles are all zeroed at the same range the ballistics (i.e. trajectory) will be identical.

Caveat; the only thing to upset the apple cart is if there is any difference in sight height above the bore center between the rifles. Still the trajectories will be the same but the impact points at various ranges in relation to the point of aim may change because of the variation in sight height. The nodes, twist, etc. ad nauseum makes no difference once the bullet leaves the barrel.

[dtknowles]

Like Larry said, the height of the sights above the bore if different will affect the perceived drop at range even if the trajectory is the same and don't forget about muzzle rise while the bullet is still in the bore. A lighter gun or stock with more drop of the comb will have more muzzle rise than a heavier gun or straighter stock.

Muzzle rise is a big variable in hand guns, in revolvers with the same barrel length and chambering, the lighter revolver will shoot the same ammo to a higher point of impact than the heavier revolver.

Tim