Bullet flight

Get or give advice on equipment, reloading and other technical issues.

Moderator: Mod

Message
Author
Tim N
Posts: 1336
Joined: Fri Jan 25, 2013 8:18 pm
Location: Branxton NSW

Bullet flight

#1 Postby Tim N » Wed Mar 13, 2019 8:33 pm

https://youtu.be/xpJ8EoGmLuE


I didn’t think a projectile would behave like that
We don't rise to the level of our expectations, we fall to the level of our training. Archilochos 680-645 BC

williada
Posts: 969
Joined: Wed Jul 22, 2009 12:37 am

Re: Bullet flight

#2 Postby williada » Wed Mar 13, 2019 9:53 pm

Great clip Tim. Sure demonstrates why testing our groups should be at a minimum of 140 yards. Wonder at what distance those babies went to sleep?

UL1700
Posts: 424
Joined: Sat Sep 16, 2017 5:39 pm

Re: Bullet flight

#3 Postby UL1700 » Thu Mar 14, 2019 7:45 am

I have always struggled to get the 108500 grain projectiles to group out of my Sherman :lol:

williada
Posts: 969
Joined: Wed Jul 22, 2009 12:37 am

Re: Bullet flight

#4 Postby williada » Thu Mar 14, 2019 9:12 am

James come back to basics mate. Perhaps it is a flinch you have developed. Watch your position, breathing, avoid snatching the trigger and don't forget to read the wind. :D

pjifl
Posts: 883
Joined: Fri Jun 17, 2005 12:15 pm
Location: Innisfail, Far North QLD.

Re: Bullet flight

#5 Postby pjifl » Thu Mar 14, 2019 10:04 am

I recently discussed this video with a few people. It is interesting but :-

More slow motion videos tracking shells show something different.

https://www.youtube.com/watch?v=vluzeaVvpU0

This is more about the development of slow motion cameras in general but it does show some shells in flight. Ignore any fin stabilized ones but at the beginning of the video is an excellent view of a spin stabilized large projectile. There is almost no coning present.


Almost no coning is evidence that the original video we watched used horribly worn gun barrels in desperate need of retubing. Any projectile, be it rifle or large gun, must have the projectile accurately aligned with the bore and not wobble around in the bore to be launched with a minimum of initial Yaw. It is why we ask for good barrels chambered with a precision beyond normal. Guns of this size can have 1/8 inch of bore wear which results in sideslap of the projectile in the bore. Once this process develops, the wear in the bore can become quite irregular as gases wash past one side of the projectile and gouge out one side of the bore. Somewhere I have seen horrific photos of 'S' shaped bore wear that can eventually weaken the gun barrel and become quite hazardous to the Gun crew. If you watch the original video carefully you will see that the projectile is really coning rather than just pitching up and down. Usually, the most accurate guns use separate projectiles initially rammed into the bore in front of a charge. Fixed artillery ammo is, however, needed where quick or even automatic reloading of the gun is more important. Like in a tank or AA gun, for example.

The coning certainly decreases to a minimum if it is stable. But it can never really 'go to sleep' although it does reduce remarkedly. This is because gravity always acts downward resulting in a path through space which is never aligned perfectly with the projectile's spin axis. The resultant unbalanced aerodynamic forces on the shell provide a torque. Thus precession occurs and the projectile realigns its spin axis partially to suite. The result is a never ending small coning motion because the gravity induced projectile path is always changing.
The key to understand is that the direction of travel and the attitude of the projectile are never the same. Almost counter intuitive.

Peter Smith.

Tim N
Posts: 1336
Joined: Fri Jan 25, 2013 8:18 pm
Location: Branxton NSW

Re: Bullet flight

#6 Postby Tim N » Thu Mar 14, 2019 6:51 pm

So the yaw of the projectile in the clip could be exaggerated due to a worn barrel?
We don't rise to the level of our expectations, we fall to the level of our training. Archilochos 680-645 BC


Return to “Equipment & Technical”

Who is online

Users browsing this forum: No registered users and 28 guests