drag, twist, and transonic flight.

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bruce m
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Re: drag, twist, and transonic flight.

Post by bruce m » Mon Apr 19, 2021 11:58 pm

a common thought here is that we all shoot, to a greater or lesser degree, in the transonic zone.
some start honestly supersonic, and some start in the transonic zone, and then if shooting far enough, go out of it.
in smokeless circles guys come out in a cold sweat, go into a flat spin, and then have a nervous breakdown just at the thought of going transonic. :shock: :?
talk to any palma shooter using a 308. :wink:
we on the other hand just do it.
palma shooters will not use the 168 gn sierra matchking, as it is very bad transonically, being a waste of time past 600 yds.
dirt diggers can be the least of its problems.
the 175 gn matchking however can easily make the transition from super to transonic, as can the 190 gn anf the 155 gn palma bullet.
this is believed due to how the air flows over these bullets.
zack has raised this issue here.
if we had to look at bullets with good airflow, 2 suspects come to mind, those being money and elliptical.
money is the old metford nose with a slightly longer ogive, and elliptical is similar to the old american long range bullet, both of which worked.
however we need more profile types shot many times for a fair comparison.
and we need to understand that the bullet in flight might be a slightly different profile than it was in the chamber prior to lighting the fire, and how to minimize that thing.
anyway, we have to work within the cards we are dealt, and that is 1/2 the fun of it.
from memory dan theodore was working with a european military 8mm cartridge.
it gave something like 2200 fps using a seriously compressed black powder pellet, and he was running spitzer bullets.
was he trying to stay supersonic to 1000 yds in a low recoil easy to shoot outfit?
bruce.
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bruce m
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Re: drag, twist, and transonic flight.

Post by bruce m » Tue Apr 20, 2021 12:34 am

just watched brian's video.
the first thing that comes to mind is the guy is a denier of spin decay.
by now we know that aberdeen proving ground found quite a bit of spin decay in 308 bullets and could measure it.
it does not matter if you start the bullet spinning fast enough to still have stability when spin has decayed.
his talk of the effects of airflow on planes IS relevant to bullets entering and leaving the transonic zone.
all these thing are forces on the bullet, and it will try to change its attitude in flight to compensate and balance the forces.
while it is doing this it is steering itself into a bigger group, and in extreme cases wobbling and even tumbling.
0ur bullets are flying for 3 seconds, which is a fair while, and a lot more can happen in that time than the 1 second of a 308 at the same range.
we need enough spin to resist all the hostile things that happen to a bullet in flight for maintainance of stability.
maintainance of stability helps maintainance of accuracy.
and with current technology it is all but impossible to overspin a bullet but easy to give it less than optimum spin.
bruce.
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martinibelgian
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Re: drag, twist, and transonic flight.

Post by martinibelgian » Tue Apr 20, 2021 5:03 am

Yup,

Dan was working with the 8mm Guedes - 8 x 60R. But around 70-80grs of powder in a 8mm (.323) bore does require some advanced fouling management...

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Don McDowell
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Re: drag, twist, and transonic flight.

Post by Don McDowell » Tue Apr 20, 2021 7:26 am

"however we need more profile types shot many times for a fair comparison."
Unless at some point in time all the shooters are on the line in the same relay using electronic targets or target pullers in the pit, and all the shooters and spotters are of equal ability, we're not likely to ever get a fair comparison.
Conditions are way to variable to come up with a "fair" comparison in this game.
Take a close look at the scores from the Desert International. Some very good shooters had bad targets at the same time not so well known shooters had really decent, and visa versa.
And if as we are thinking is going to happen, when the article in the next BPC news comes out about the equipment list for the Desert International, there's going to be some information in there that is going to make some's collective heads explode. :D
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Don McDowell
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Re: drag, twist, and transonic flight.

Post by Don McDowell » Tue Apr 20, 2021 7:39 am

I'll take it a bit further on the "fair comparison"
Unless at some point in time you have say 5 of the consistently top placing shooters, shooting identical rifles, and paired with their preferred spotters, all shooting ammunition meticously loaded by a 3rd party, all shooting the same bullet at the same time, and using the same fouling control, we'll probably never get a true fair comparison.
This game isn't high-power, and it certainly isn't anything even remotely similar to the old days of Camp Perry following the Creedmoor era, when shooters showed up and were issued a rack rifle and ammo can.
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Distant Thunder
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Re: drag, twist, and transonic flight.

Post by Distant Thunder » Tue Apr 20, 2021 9:07 am

I can't remember if I posted this before but it is very interesting and about the best information I've found that relates closely to BPTR.

Watch it and let's hear what you think!

https://www.youtube.com/watch?v=HpDKxVuRWto
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Don McDowell
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Re: drag, twist, and transonic flight.

Post by Don McDowell » Tue Apr 20, 2021 9:45 am

I think there may be some similarity on that. Given velocity nose shape etc.
But the one thing that causes some difference might be in that in Creedmoor the bullets flight path often will rise above the range flags and into conditions that aren't easily or readily detected from the rifle/spotter level. And anyone that has ever spent time checking stock water windmills can tell you there can be a ton of difference between what the wind is doing at ground level and what's going on at the top of a 25-30 ft windmill tower. Linemen can tell you that what's going on down on the ground with the grunt, can be a bunch different than what's hitting him stuck to a pole with his hooks and belt 35 ft off the ground.
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Distant Thunder
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Re: drag, twist, and transonic flight.

Post by Distant Thunder » Tue Apr 20, 2021 11:25 am

The can certainly be different at 40 feet than what we see in the flags, but I think our bullets deal with many of same things air gun pellets deal with in the transonic zone. The pressure wave caused by air flow is key amount them. That pressure wave is not stationary either, it moves forward (I think) as the bullet slows down and can be very unsteady at certain velocities.

It's also interesting that the nose shape plays a part in where and when the pressure wave occurs and how it moves.

I have found a lot about this subject of air flow as it relates to aircraft, this airgun stuff is the closest to what our bullets go through on the way to the target at 1000 yards that I have come across. I do believe nose shape plays an important role in minimizing the effects of transonic flight.

The other thing that is interesting is that there are certain velocities within the transonic zone that have more detrimental effects on a projectile than other transonic velocities and one of those velocities occurs around 900 yards with many of our cartridges. That velocity being around 900 fps as a bullet comes out the bottom of the transonic zone.

Like others I have experienced some problems at 900 yards with certain loads/bullets. I seem to have gotten around that with my current combo.

The wind is a variable, I think the ballistic phenomenon of the transonic zone is more of a constant and can be minimized if understood. If understood! Until someone with extensive knowledge and equipment and a bunch of time does a study of BPTR bullets we can only look to things that have been studied already and are at least similar to our bullets as they travel through the transonic zone.
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A new age of tyranny dawns in the United States! If anyone is brave enough to say so they're destroyed by the BIG Tech branch of the Federal Government for spreading lies! "Reeducation" camps to follow!

semtav
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Re: drag, twist, and transonic flight.

Post by semtav » Tue Apr 20, 2021 12:10 pm

I realize gong and Bptr are 2 completely different animals, but talking about the 900 yd issue brings a different but casual observation from the back of my noggin.

Our 900 yd target is a diamond, and most find this shape more intimidating, but quite a few times, when I think someone is down and out of the picture, they pull a real good score off on the 900.

Not sure what to attribute that to, possible because if you get your elevation right your windage errors are more forgiveable ??

And if that is the case then there is nothing wrong with the load. Only knob twisting errors.

Maybe this is only a local phenomenon.

Or maybe their losd is perfect for 900 and wrong for the rest

mike herth
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Re: drag, twist, and transonic flight.

Post by mike herth » Tue Apr 20, 2021 12:25 pm

Geeze Brian, I was looking forward to an enjoyable and worry free shooting season at Forsyth. This topic and barrel torque rotation make my hair hurt.
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charlie young
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Re: drag, twist, and transonic flight.

Post by charlie young » Tue Apr 20, 2021 4:05 pm

I like the 900!! It's a get back in the game moment if you can get 'er dialed in!!

bruce m
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Re: drag, twist, and transonic flight.

Post by bruce m » Tue Apr 20, 2021 5:11 pm

Don McDowell wrote:
Tue Apr 20, 2021 7:26 am
"however we need more profile types shot many times for a fair comparison."
Unless at some point in time all the shooters are on the line in the same relay using electronic targets or target pullers in the pit, and all the shooters and spotters are of equal ability, we're not likely to ever get a fair comparison.
Conditions are way to variable to come up with a "fair" comparison in this game.
Take a close look at the scores from the Desert International. Some very good shooters had bad targets at the same time not so well known shooters had really decent, and visa versa.
And if as we are thinking is going to happen, when the article in the next BPC news comes out about the equipment list for the Desert International, there's going to be some information in there that is going to make some's collective heads explode. :D
don,
you don't seem to be on the page, as in you are coming at this from the wrong end.
we are talking about stability in the transonic zone, and winning matches is not how you test for it.
as we know, winning long range matches is primarily about wind reading.
that said, you do require the mentality to have bullets that fit properly and work up a load to make wind reading worthwhile, and even to learn how to do it.
you don't need a wind coach to test for stability.
all you have to do is put holes in a piece of paper, and establish elevation settings for the distance, and measure vert.
if you are getting dirt diggers etc you have to nail that stuff down first.
stable bullets give round holes.
less stable bullets have more vert in the group.
in your case, having your own range is a fantastic opportunity to do this.
once you have established the most stable bullet with the highest b.c. possible, then is the time to use that to give yourself a better chance in competition.
i was not so lucky as you and had to hire a fullbore range, supply my ownn target marker, and shoot from 300 to 1000 yds over a period of years.
it took so long in part because i had a series of bullet moulds made during the process based on data collected up to that point.
i also shot in a fullbore club with smokeless shooters, and the markers there were helpful.
they took photos of bullet holes and gave verbal reports afterward to compliment that.
in the end i had a bullet so stable that one went through 3 wind flags and still hit the target nose on, but a little low.
the long and short of it is that i can forget stability and just focus on the wind.
bruce.
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Don McDowell
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Re: drag, twist, and transonic flight.

Post by Don McDowell » Tue Apr 20, 2021 5:46 pm

Bruce, it's an very interesting thing when the sun and humidity are just right and you are able to watch the bullet, not the trace as you see in high-power stuff, the actual bullet drop into the target. What's really fun is when at distances beyond 600 and you can watch bullets that come in on a good flight path, and the bullets that have lost stability at some point along the way and they look like they're coming in on the hand rail of a circular staircase. Still in mostly level flight, but still traveling in big wide circles, giving high and low and left and right impacts most times completely off the target. Have also caught a few times when the bullet would drop into the scope looking to be a good center hit, and just before it gets to the target and the little bullet jockey looks up and says holly crap, grabs the stick drops the flaps and gives it full throttle and over the top it goes.
If a bullet is leaving oblong holes, either the velocity is to low, or the bullet length to long for the twist.
Concentrate on what the target tells you , keep the vertical in test loads to a minimum, and the rest will fall together, if the shooter does his/her part.
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desert deuce
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Re: drag, twist, and transonic flight.

Post by desert deuce » Tue Apr 20, 2021 7:48 pm

Donnie Ray Wrote:
If a bullet is leaving oblong holes, either the velocity is to low, or the bullet length to long for the twist.
OR, consider the possibility, especially if not all holes are oblong, that the oblong bullet hole may be evidence of a bullet strike that the bullet has not returned to the stable attitude after being disturbed in flight by conditions?

The issue here is that it is usually in bullet flight path disturbance we shoot in. So, all bullets we use are subject to disturbance by mostly wind effects.

What Dan T. and I were drifting toward was a combination of bullet design characteristics combined with rifle and shooter characteristics that were in a balance that minimized the amount of deflection and would hold relatively constant during a timed string of fire, as in a match. Which are/were limiting parameters.

As for the bullet design he was focused mostly on the nose shape and center of mass of the bullet, as in weight forward or rear. I only wanted the best bullet design for BPTR Long Range.

I wrote about this in Black Powder Cartridge News in a "Balanced Load" article specifically for shooting in BPTR "Long Range" Competition.

The formula ended up being two DT $ designs, one .44 cal, one .45 cal, both for 16 twist barrels by Paul Jones. So what was the result you say?

I can't quantify the result or really explain it, BUT, I am sticking with it after the target proving to me it is the way to go.

The difficult part is identifying and achieving the optimum balance of shooter, rifle, load on an individual basis.

You can read all about the application of this approach in the upcoming issue #144 in Black Powder Cartridge News Phoenix Match Results.
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Don McDowell
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Re: drag, twist, and transonic flight.

Post by Don McDowell » Tue Apr 20, 2021 7:57 pm

I some times wonder too, if base finning might upset the spin and balance of a bullet on it's trip down thru all the pit falls it will encounter in thermals, sheers and the like.. especially as the range tends to go past 800.
Or possibly even a small void in the bullet that while not big was enough to allow the casters weight variance?
We know for at least mostly sure, that nose slump can cause all sorts of anomoly.

But problems at any given range could never be attributed to anything the yanker of the trigger did....
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