Ensuring absolute concentricity of muzzle devices

[Uncle Ogre]

The bullet is going supersonic, so it should be way ahead of the gases that follow it (since there should be *zero* preceding it if the bullet is sized correctly and you don't have gas blow-by)

Exactly this.

If the bullet is way ahead of the gasses, what is pushing the bullet down the barrel?

And once the bullet leaves the barrel and begins to slow, what happens to the still expanding gas behind it?

The OP may be overestimating the magnitude of the effects, but his grasp of the physics of gas expansion past the bullet while still in the muzzle device is pretty solid.

[video=youtube_share;7y9apnbI6GA]http://youtu.be/7y9apnbI6GA?t=9s[/video]

 

[vicorjh]

Paper from Hornady that discusses the effect (muzzle brake): http://www.hornady.com/assets/files/faqs/AxialFormFactor.pdf

The Cd plots show significant impacts to the drag of the projectile versus no brake, especially at high supersonic Mach numbers, right out of the muzzle. Most of the brakes show significant “tipoff” of the projectile at the muzzle which causes yaw and takes substantially differing amounts of time to damp. Most of the brakes tested will have an adverse effect on the drag and associated performance of the projectile. Brake D may have some advantage over the no brake because of only a small impact to the high supersonic drag and significant reduction in drag at lower supersonic speeds. If a brake is a necessity Brake D would certainly be the one to use with this setup.

What this means in real-world could use some interpretation.

Discussion from the interwebs: https://www.reddit.com/r/askscience/comments/17p16j/what_happens_when_a_projectile_breaks_the_sound/

Under normal circumstances, gasses shouldn't leak around the projectile in the barrel. Because of this, a projectile within the barrel doesn't break the sound barrier until it exits. The speed of sound in steel is much faster than in air.
The gasses ahead of and behind the projectile are under extreme pressure and the gasses proximal to the projectile are moving with it. Once the projectile exits the barrel, it's relative velocity is greater than the speed of sound and this transition happens right at the muzzle. This is one of the (though not the biggest) reasons why the condition of the crown (exit of the muzzle) is critical in a rifle's accuracy. The regularity of the pocket of gas encapsulating the projectile (part of which follows the projectile down range) plays a role in the regularity of its trajectory.

Edit: The gasses themselves can form compression waves that break the speed of sound. These waves interact to form what are known as shock diamonds.

 

[warwickben]

Not sure if it's been said . But you'll need a 4 jaw and spider on a lathe and set of pin gauge . Dial it in to spin true . Then single point thread .


Sent from my iPhone using Tapatalk