Bullet flight

[kwyeewyk]

This seems like it should be obvious and maybe it's a stupid question, but got thinking about it and decided I didn't know. With a pointed bullet, does the point follow the ballistic path of the bullet, i.e. first pointing up through the arc and then pointing down as it travels further from the barrel, like an arrow? Seems like it would, I assume the spin would keep the tip along the ballistic path, but it also seems like the tip would be lighter than the tail, so if you were to shoot straight up, once the bullet stopped, would gravity just pull it straight back down tail first rather than the tip inverting and coming down tip first like an arrow?

 

[std7mag]

I'm not really sure, especially in long to extreme long range.
I've seen illistrations from several sources where the nose is still pointed up through the ballistic arch.
As you mentioned, the center of gravity tends to be more rearward.

Then there's the issue of going subsonic at extreme long range.

 

[midwesthunter]

Short answer is no it doesn't. Bullets center of gravity, aerodynamic drag and wind vector dictate the way the bullet points along its flight path.

 

[VikingsGuy]

I can't speak to bullets, but more generally spinning cylindrical objects that fly in an arc do tend to exhibit an "axis tipping" phenomenon as long as they are spinning fast and are otherwise stable. Apparently, when the axis of the cylinder is no longer aligned with the axis of its path there is a small gyroscopic torque that forces the cylinder to move its orientation closer to that of its flight path. It's possible that bullet shape somehow creates opposing forces that limit or prevent this, but if I had to guess (and a guess is all it is) I would expect stable spinning bullets to "tip over" if you will. Otherwise, as a bullet's path through air is dropping there would be increasing force (air friction on the underside that would encourage a "back flip" if you will.

 

[Gut Shot]

Yes the point of the bullet follows it's trajectory. But for different reasons than a fletched arrow because they are stabilized differently. There is a reason artillery fuses are on the pointy end of the projectile.

 

[kwyeewyk]

I had done a couple quick searches and mostly came up with safety stuff saying not to shoot in the air. When I searched "what happens if you shoot straight up" found a lot, turns out it was on myth busters. Sounds like if it's shot perfectly straight up it will lose it's energy and then tumble back down reaching terminal velocity, which they said probably wouldn't be enough to kill you. If it's at all angled they say it will keep it's spin through the arc and continue to travel tip forward with higher velocities and would be likely to kill somebody if it struck them. I guessing it's probably nearly impossible to shoot straight up without some type of mechanical aid, and even then probably hard due to wind drift, etc.

 

[Gunner46]

Arm chair, beer drinking thinking, too much about too little. Inside responable ranges there is NO reason to even consider the physics entailed. Ya don't need PHD to drop a 'Lope, Deer, Elk, Pig, or any other anything. Responsible range, quality bullet, sufficient energy, shot placement.....Done.

 

[kwyeewyk]

Arm chair, beer drinking thinking, too much about too little. Inside responable ranges there is NO reason to even consider the physics entailed. Ya don't need PHD to drop a 'Lope, Deer, Elk, Pig, or any other anything. Responsible range, quality bullet, sufficient energy, shot placement.....Done.

Yes my wife has told me I spend too much time thinking about things that don't matter! I was pondering trajectories and got to thinking about what would happen if you shot so far that the bullet was basically coming in from above, would it be enough of an angle that you'd need to adjust shot placement (clearly nothing I'd ever attempt while hunting). Turns out that even at 5000 yards a 30-06 round would only be dropping a few inches per foot (but would have dropped nearly a mile) so yes, nothing to ever worry about again!

 

[Gunner46]

Yes my wife has told me I spend too much time thinking about things that don't matter! I was pondering trajectories and got to thinking about what would happen if you shot so far that the bullet was basically coming in from above, would it be enough of an angle that you'd need to adjust shot placement (clearly nothing I'd ever attempt while hunting). Turns out that even at 5000 yards a 30-06 round would only be dropping a few inches per foot (but would have dropped nearly a mile) so yes, nothing to ever worry about again!

Well, to answer the question. As long as there is enough spiral to maintain stabilization the bullet will keep course, with the nose in front. Once the stabilization is lost the center of mass will take over, where ever that may be.

 

[FLS]

It should stay stable in until it goes subsonic, once it does different designs will behave differently. We have a range where we can shoot out to a mile. At one mile some of my buddies 308 bullets were hitting the steel sideways.

 

[diamond hitch]

Seems like somewhere I read that the early m14s in Nam had a spin ratio that caused them to tumble. I think they said that changed half way through the war to get more uniform trajectories. I guess the same could effect bullet prrformance in hunting rifles.

 

[Laelkhunter]

Seems like somewhere I read that the early m14s in Nam had a spin ratio that caused them to tumble. I think they said that changed half way through the war to get more uniform trajectories. I guess the same could effect bullet prrformance in hunting rifles.

I think you are referring to the M-16. Supposedly the bullets would "tumble" which can be easily mis-proven by shooting at a cardboard target at distances, and the bullets still make round holes. If it tumbled, it would leave odd shaped holes in the target depending on how the bullet hit, and the accuracy would degrade so quickly the bullet might not even hit the intended target. I think what was inferred was that the bullet would "wobble" along it's longitudinal axis which means the tip of the bullet kept going straight on the line of trajectory but the bullet base might wobble a little in a circular motion, and when it hit it's target (enemy soldier) then the bullet actually tumbled and usually broke into pieces at the cannelure, and the front part (tip) flattened out. I think I heard that somewhere- Could be poppycock.

 

[diamond hitch]

I just found an article "Bullet twist rates" by David Sams that discusses the change in twist rates in the M16 over time and why. It provides insight to twist rates and bullet weights. I don't know if the same relates to heavier calibers but being old school, I have always shot 175 grain in my 7RM and 180 gr in my 06 with consistant success (97-98%). As I watch an evolution to lighter bullets I question if we will see a change in barrel twist rates to match them. It won't change much for me as I have ample supply of rifles and matching bullets for my last 15-20 years. I am just curious as to the effect on accuracy of bullet changes on existing older weapons given this article.

I bought a box of Hornady ELDX and will continue to experiment with them in various situations but probably won't hunt with them in my last years. What has worked for the last 50+ years is likely what I will follow but supply changes have forced me to stockpile components due to lack of trust in the suppliers to continue.

I don't expect anyone to change anything they do based on my experience. I just know what has worked for me over all these years.

 

[Laelkhunter]

I think the change in twist for the M16 barrels are now as fast as 1/7. These barrels are designed for shooting and stabilizing heavier (thus longer) bullets up to 77 grains, and maybe even heavier. I too notice the trend for shooters going to lighter bullets after all these years of heavier is better for big game. However, due to the mono bullets, supposedly the same (or better) performance can be achieved by reducing the bullet weight 10% when going from a cup & core to a mono. For example, I went from a 180 Nosler Partition to a Barnes 168 TTSX in my 30/06 and went from a 250 Nosler Partition to a 225 Barnes TTSX in my .340 Weatherby, and have not noticed a drop in performance in either caliber. I did not change the barrel (twist rate) for the lighter bullet, but I'm sure if I went down to the minimal weights in each bullet caliber mentioned above, I would have to rebarrel to a different twist rate to stabilize them or to achieve max accuracy.

 

[1_pointer]

I think the change in twist for the M16 barrels are now as fast as 1/7. These barrels are designed for shooting and stabilizing heavier (thus longer) bullets up to 77 grains, and maybe even heavier. I too notice the trend for shooters going to lighter bullets after all these years of heavier is better for big game. However, due to the mono bullets, supposedly the same (or better) performance can be achieved by reducing the bullet weight 10% when going from a cup & core to a mono. For example, I went from a 180 Nosler Partition to a Barnes 168 TTSX in my 30/06 and went from a 250 Nosler Partition to a 225 Barnes TTSX in my .340 Weatherby, and have not noticed a drop in performance in either caliber. I did not change the barrel (twist rate) for the lighter bullet, but I'm sure if I went down to the minimal weights in each bullet caliber mentioned above, I would have to rebarrel to a different twist rate to stabilize them or to achieve max accuracy.

Twist rate is impacted by bullet length, not twist. Mono bullets are less dense than those with lead, so are longer (for the same weight) and can require a faster twist rate. With twist rate, too fast is better than too slow.