The Mysterious BC compliments of Ted

[Saltlake58]

Ok, now i m hesitating again. When seeing this subsonic-supersonic differences in air movement, subsequently those explanations on the white board with subsonic for a brief ‘transsonic' moment becoming supersonic in its waves-movements.
‘Transsonic”? Wth ?
Got to say i never knew this.

So just to make sure i understood this right, please correct me if i m interpreting wrongly :
A subsonic – but very close to supersonic – traveling bullet creates supersonic shockwaves for a very-very brief moment pulling/jerking the subsonic bullet into supersonic flight, immediately after that going subsonic again.

Or did i miss something?

As others on YouTube posted, weird stuff happens in the Transonic zone. It looks like the bullet can be subsonic, but airflow around the bullet may be in the transonic or supersonic range. Talk about screwing up any ballistic calculation. I think you are really close, but as stated, I'm no fluids specialist and only watch the stuff for a hobby.

 

[Reg Creep]

The slug is not achieving supersonic speed. Some of the air around the slug is is being accelerated to supersonic speed due to the "airfoil" like shape of the slug. The speed of the slug itself is not affected by this.

 

[Saltlake58]

Oh, one more thing. My FX chrony's range is something like 580fps to 1100 fps. I wonder if the slug actually went supersonic and the Chrony only reported 1100 fps when it was actually higher. Maybe try a different chrony with a higher range??

 

[Tomygun1]

Airgun Nation Admin,

Watching your YouTube videos and digesting the high velocity testing that you are doing I can only say thank you for what you are doing. Like you I have discovered that velocity is not the enemy of accuracy. People seem to measure bc mostly for lower velocity variants to achieve expected accuracy results at those speeds. Thats fine, but very restrictive, like pushing a rope…. All projectiles from air rifles are subject to bc variants at any speed as well as powder burners from 1200fps to 4500fps. I stumble as to just why the pcp experts continue to tell us that this is a barrier. Pellet skirts limit bc and that is hard to get past, some are better than others. But that is a projectile design problem, not a velocity problem. While I have heard the ‘experts’ argue that exceeding 940fps at 100 yds will deteriorate velocity due to more drag (lag time) I don’t hear anyone talking about ‘time of flight’ and the benifits aquired when it gets there faster with less drift.
Keep up the good work!

 

[caesar]

So , one would have to use something like a Labradar or chronograph at the target to confirm whether indeed there is a change?

Allen

That’s what I’ve always done. Two chronographs

 

[dgeesaman]

Time to get that rig shooting next to a Labradar and see if the velocity data gives the same BC results.

.22LR runs around 1100fps, and has BCs under .15. So I think the actually velocity data won't give a .18 BC.

Barrel harmonics make the most sense. Transonic air flow regimes likely reduce BC, not improve it: https://www.sierrabullets.com/exterior-ballistics/22-rimfire-ballistic-coefficients/

If PA and WI weren't such an awful long drive apart I'd offer to bring one by. But there are surely LR units much closer than that.

 

[hgatesm]

Deriving the BC from a POI change is valid only from the same state of tune. Changing the state of tune influences the recoil characteristics of the gun in unpredictable ways (e.g. barrel harmonics, muzzle flip, etc.) and therefore has the potential to produce very misleading differences in POI.

In Ted's example, he moves it from 1000fps to 1100fps which amounts to a significant increase of muzzle energy of 20%. Much more air delivered during the shot cycle...much different movement from the gun and the barrel.

Watching this video I was thinking the same thing, I have nothing but a world of respect for Ted and what he does. Honestly a big fan, but he missed the mark on this one. Changing the ammo factor alone is one thing. Changing all the harmonics of the rifle, completely sperate and should be talked about separately because they are in fact different and each do matter.