Going Transonic

[Fudmottin]

We all know the dogma. When a bullet goes transonic, accuracy goes away.

Has anyone actually experienced this? I'm wondering if groups from 240 SMKs loaded to 1050fps would suddenly explode in size if the same round was pushed to 1200fps, clearly faster than sound.

Or would the bullet just switch to whisper mode and continue along its merry way because it is not a Bell X1?

I'm just thinking ahead for a flatter trajectory to knock down rams on the 500 meter line. Maybe transonic loads could work for heavy bullets. Or maybe the bullet just decides to fly off in a random direction as the mean aerodynamic center changes during the transonic phase of flight.

[cav_scout_tj]

I conjecture that the "transonic destroys accuracy" idea comes from 308 shooters reaching out to 1000 yards and beyond. At that point the rotation rate has degraded to point where it can no longer stabilize through the transonic transition.

I think that heavy bullets though a 1:8 twist barrel at launched at 1200fps will maintain accuracy, and no fall apart when going transonic.

An interesting read

[Rikky Lee]

Think of it more like a spinning top moving slowly across a flat surface.

The 240 grains spin very fast and only have a short range - they remain stable beyond a short range. So the top moves slowly towards this target (say 6inches) loosing spin rate slowly.

Move the expected range exponentially - say 20 - 24 inches - the spin rate will start to slow and the top's movements start to become erratic before stopping. This erratic phase is similar to transonic in long range shooting.

[HUNTER2]

As long as the bullet stays supersonic, it will stay accurate (assuming everything is as it should be, twist, etc...) until it passes from super to sub. The supersonic bullet ( or whatever ) has the shock wave on the nose. Subsonic has the shock wave at the rear. I currently shoot 4 different rounds subsonic with the bullets reversed to take advantage of this and the large frontal area. The 454 with a 300 gr. hornady is unreal in the acc. dept. The drag areas change places when trasversing from super to sub...It is during this time that the bullet, plane, etc. experiencies turbulances. It will degrade accuracy during this event! But I have seen no numbers that says how long it takes to transform from one to the other, or how much acc. will suffer. Black powder shooters go through this zone ( 1,000 yd. matches )without any apparent problems, but they shoot some huge projectiles!!!!! Try it out on the range and see if you can tell any difference on out there. From what I was getting from some of the post on here, the 240 is close to borderline stability. If a bone was hit, the exit hole would become a knife like slit where the bullet had tumbled. Get back to us and let us know how it turns out.....

[Fudmottin]

OK. It doesn't look like I am slapping the face of orthodoxy here.

Here's my current situation. My barrel has been machined and should be parked on Wednesday if all goes to schedule. With luck, I will have it in hand sometime next week, ready to shoot. I won't have a suppressor for some time :(

On the ammunition front, I have some leftover 220 SMKs I was thinking of using to fire form some brass that I got from 320pf. I also have 240s, but I want to save them for formed brass. I've got all the dies I need.

Hopefully I can tell the difference between sub and super by ear. I have a chrony F1. It's pretty basic and does not remember shot velocities for printing out. But it worked last time I took it out. I mention this because I don't know _when_ a round will make the transition.

And I certainly have no way of telling how quick the transition is! Anyone want to fund 200 ten thousand frame per second cameras for setting up along a firing line at 1 meter intervals? Or perhaps 20 would be enough at ten meter intervals.

As a post script, I would like to mention something Julian Hatcher wrote in his notebook. When firing bullets straight up, most of them fell base first. So they do keep spinning. While the rifling will obviously make the air flow non-laminar (at least that would be my expectation), I don't know what sort of drag force there is on the spin of a bullet. Spin slows down a lot less rapidly than a super sonic bullet does though.