FX M3 @ 1100fps Results might surprise you !!!

[MongooseV8]

1050 youre on edge of being trans-sonic, 1150 will keep you in supersonic. You always want to be above super or below, never in the middle.

Yes exactly the point. Depending on your elevation and weather conditions, most of us try to get close to the first zone without going over. If you go over you actually disturb the projectile 4 times. Since you cannot stay above super sonic with any pcp it only works to your disadvantage to approach the sound barrier let alone go over it. You will start to get a disturbance about 0.8MACH1, increasing more til you cross the sound barrier. Both exiting and entering the sound barrier will jostle the projectile too. All of it works against us in the air world, so we usually stay under.

 

[weevil]

Air turbulence in the transition is predicted to peak at 1125fps, give or take a little based on temperature. Speed of sound varies very little with altitude/pressure. Not sure how four “disturbances” are predicted because a projectile is stabilized in the barrel and cannot accelerate after its exit. For the most part, speeds above 1000-1050 (with slugs) are contra indicated because drag increases rapidly thereafter, which in any case very quickly decelerates them to below those speeds. So, it’s really only a little wasteful in terms of air/energy but there is nothing inherently wrong with shooting slugs at 1100fps MV. If it is a sweet spot for the harmonics of the barrel/projectile then count yourself lucky that you’ve found one. @wooferocau’s results are stellar!

 

[CrashKT]

Air turbulence in the transition is predicted to peak at 1125fps, give or take a little based on temperature. Speed of sound varies very little with altitude/pressure. Not sure how four “disturbances” are predicted because a projectile is stabilized in the barrel and cannot accelerate after its exit. For the most part, speeds above 1000-1050 (with slugs) are contra indicated because drag increases rapidly thereafter, which in any case very quickly decelerates them to below those speeds. So, it’s really only a little wasteful in terms of air/energy but there is nothing inherently wrong with shooting slugs at 1100fps MV. If it is a sweet spot for the harmonics of the barrel/projectile then count yourself lucky that you’ve found one. @wooferocau’s results are stellar!

Shooting through the speeds of sub, trans, going into super isn't bad. It's when it slows down, that's where the issues lie.

 

[MongooseV8]

4 Disturbances come from:

Vibration approaching the sound barrier
Breaking the sound barrier
Slowing down and going back down below the sound barrier
Vibration while slowing near the sound barrier

This applies to all objects traveling through the Earths atmosphere, even in the barrel. Granted, like you say a projectile has the help of rifling to keep it stable. But after it leaves the muzzle it will be subjected to disturbance(s) not seen at slightly lower speeds. You can still get good accuracy at these faster speeds, but that is not normal.

 

[wooferocau]

Me again...

More this evening.... 350yds ... very small gentle breeze..

My stuff up.... dope was a little low.... group fell in lower plate section with some hitting the legs and a couple in between. The majority was spread over 5 - 6 inches ....one "flyer" up on top plate edge..

Sooo... majority went 1 1/2 to 1 3/4 moa still quite reasonable ( and consistent) at this distance..

 

[MongooseV8]

That sure is a nice looking place to do some slug testing