drag, twist, and transonic flight.

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bruce m
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drag, twist, and transonic flight.

Post by bruce m » Wed Apr 14, 2021 4:41 am

smallarms bullets will trace with trajectory, regardless of stability factor.
the myth of over stabilization likely comes from large caliber artillery guns with very high angles of fire. those projectiles which weigh 100s of pounds, and are launched at over 30 degrees can reach heights where the air is thin, and the projectile velocity at apogee is slow with low dynamic pressure to orient the projectile, and the moment of inertia is so high (a lot of spinning mass), that such a projectile can fail to trace, and fall to the ground base first.
but there are a lot of differences with small arms. bullets are much lighter, don't slow down at apogee, don't get that high etc. in fact the more stable a bullet is, the better it will keep its axis aligned to the flight path.
live fire radar tracks of small arms rounds show reduced drag for all speeds, ESPECIALLY TRANSONIC, for bullets fired from faster twist rates, all else being equal.
this includes the falling part of the trajectory.

the above is by bryan litz and lifted from another site.
take from it what you will.
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Re: drag, twist, and transonic flight.

Post by bruce m » Wed Apr 14, 2021 4:47 am

i find the above interestin in relation to my own experiencs, which suggest that a stability factor of 2.0 is vastly superior to 1.5 when shooting through the transonic zone, as in creedmoor ranges and further.
the reduced verticle that results i am certain comes from bullet stability that can so easily be disturbed when going through transonic.
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desert deuce
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Re: drag, twist, and transonic flight.

Post by desert deuce » Mon Apr 19, 2021 12:08 am

Bruce M wrote:
the reduced verticle that results i am certain comes from bullet stability that can so easily be disturbed when going through transonic.
As I recall this is first I have seen the word "disturbed" used to describe the phenomena of when the bullet goes through the transonic zone.

This is a point Dan T and I tried to flesh out and apply to long range shooting. We agreed that it exists but that was about as far as we got. The first variable of course is that at some point the bullet must be super sonic for any "theory" to be viable. The second variable of course is at what point in the flight path does the bullet go subsonic and where does this transonic zone occur?

Last but not least the ability of the bullet in flight to resist the force destabilizing it in the transonic zone. Which implies a return to improved stability from the disturbance.

We discussed where a bullet goes to sleep, bullets that do not achieve speed of sound and distances to target that do not present a transonic zone.

The whole idea of formularies that predicted results at 1,000 yards based on results on targets at 100 yards was discarded early.

Take it away Bruce.
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Distant Thunder
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Re: drag, twist, and transonic flight.

Post by Distant Thunder » Mon Apr 19, 2021 6:54 am

I often see what appears to me to be a misunderstanding of what the transonic zone is or perhaps better stated where it is.

It isn't just a very narrow velocity that starts just above the speed of sound by a few fps and ends just a fps below the speed of sound. It's actually starts at 1346 fps and continues all the down to 897 fps. So to be above the speed of sound (1125 fps) is not necessarily above the transonic zone, but just starting out below the speed of sound does not necessarily avoid the transonic zone either.

A look at ballistic table for most black powder cartridges will show that they pretty much all start out in the transonic zone and remain in it throughout their entire flight to the target even at 1000 yards.

Even a 550 grain 45 caliber bullet starting out at 1400 fps will enter the transonic zone well before 100 yards and will be at the speed of sound at around 300 yards. It will not drop below the transonic zone until around 900 yards. So that 550 grain .45 caliber bullet will be in the transonic zone from about 50 yards all the way to 900 yards or so!

I hate to break it to you, but we are in the transonic zone! Learn to deal with it. And while we are in the transonic zone our bullets are subject to all the nasty effects of the transonic zone that so many shooters try to avoid, but can't.
Jim Kluskens
aka Distant Thunder

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 » Mon Apr 19, 2021 7:56 am

This oughta be good for an evening of entertainment !!


Just to help keep the entertainment lively :
https://www.youtube.com/watch?v=lXODyVnE_Dw

Kenny Wasserburger
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Re: drag, twist, and transonic flight.

Post by Kenny Wasserburger » Mon Apr 19, 2021 10:57 am

Jim I believe you have the crux of the subject well in hand, and understand it.

Dave Gullo and John Venhous, were pulling my target at the 2018 Midrange Nationals at Raton, at a dinner that evening at the Icehouse, Dave quite candidly informed all of the 10 or 12 people in attendance that my PP bullets were still above the speed of sound when they cracked coming into the pit at 300 yards

Dave also pointed out, that I was 3rd at 300 that day and was the top Score at 600 for the day besting all comers. The day two match I took 3rd on the very difficult 500 yard target. Dave had an excellent spotter in John Venhous, as did myself in Huey Wilson a veteran of Raton.

The rifle used was Dora, my 45 2-7/8ths 25# rifle, it has a 16 twist, load was 103 grs of 1.5 Olde Eynsford powder it chronos at 1420 fps avg. That load was was determined by load testing at 200 then 600 yards at my range at the ranch. The chronograph numbers were only determined after load testing. I believe our focus, needs to be in these areas for success.

My thoughts are, a bullet with the least amount of drag in our game is the PP bullet. With a proper twist that will maintain bullet stability further, and through the conditions will have the advantage. Testing at 1 mile tends to bear this theory out.

A 518 gr Money bullet, and a 525 gr NASA bullet were tested at my mile match. Both bullets used the same brass, the exact same load, including wad Stack. The PP bullet required 40 MOA less Elevation than the Mono-groove NASA bullet. Both were tested with my 34 inch barreled Shiloh The Hell Bitch. The barrel was put in by Kirk in 2005 it has a 1-18 twist. MVA XLR rear sight.

My point is: All of our bullets must contend with the transonic Range as you so pointed out. To better deal with this, bullets that require less time in flighty and better BC that yield flatter trajectories are necessary, and faster twists to better maintain stability.

Due to our choice of material for our bullets, we are constrained by the limitations of a cast or swaged bullet design, as we are by our choice of powder. We can mitigate some the limitations of the lead by alloys of course. I have shot some very good scores with 10-1 alloy, yet no better than my 15-1 or 16-1. Initial testing shows promise with this 15-1 alloy using the 95/5 tin-antimony solder that we first learned from Kurt Altenburg. Proof will be in its performance at Alliance Neb long range match the first weekend of May.

The fact that the Antimony sweeten alloys shot 5.3 MOA flatter at just 200 was a surprise, with the exact same load I used with my Money PP bullet, I believe it had more to do with bullet design that alloy though, yet the alloy did not hurt either.

Still flatter trajectory and less time in flight during our bullet’s struggle through the trans sonic range, are all good things in my opinion, and should be our final goal.

Another nail you hit squarely on the head, 900 yards, we have always wondered what was going on at 900 yards because something does. Dropping to subsonic, is what’s happening. Zack Taylor has mentioned this enough for one to pay attention to his opinions, which I value. I know he uses a different load just for 900 or he used to at least.

Some random ramblings this Monday as we have 4 inches of snow and a winter weather advisory till 9pm tonight.

Kenny Wasserburger
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Wyoming Territory Sharps Shooter

Kenny Wasserburger
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Re: drag, twist, and transonic flight.

Post by Kenny Wasserburger » Mon Apr 19, 2021 11:19 am

Bruce,

I also believe your observations on twist are fundamentally correct, and bullet alloy and design also play into it, your first posts on the dual Diameter bullet, got my attention. My own very limited tests show a faster bump up to groove with the dual diameter bullet show a great deal of promise in elevation reductions.

Kenny Wasserburger
We'll raise up our Glasses against Evil Forces, Singing, Whiskey for my men, Beer for my horses.

Wyoming Territory Sharps Shooter

mdeland
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Re: drag, twist, and transonic flight.

Post by mdeland » Mon Apr 19, 2021 3:37 pm

All this makes me wonder why the long 38's should not be a top contender at long range. With some good linotype alloy and 10 twist barrels it should be possible to get some of these 38 cal pills going over 15-16 hundred without stripping. I still think Dan T. was on the right glide slope with his 38 thinking and just needed some more time to develop his ideas.

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

Post by bruce m » Mon Apr 19, 2021 6:00 pm

good to see some long range heavyweights weighing in here.
by that i mean individuals who have done a lot of it and have been observant.
when these type of people start to talk, things come to the surface.
the 900 yd syndrome has been mentioned for years, but never delved deeply into.
looking at bullet stability, we believe that a bullet spinning at sufficient rate to be stable in a vacuum and under no gravity will keep spinning for ever in a stable manner.
as we have to fire our bullets under the influence of gravity, this force acts on the bullet making it try to fall to the ground.
here is the first force acting on the bullet
the bullet comes out of the barrel with its axis exactly on the axis of the barrel.
as the force of gravity moves the hopefully stable bullet towards the centre of the earth, its axis will realign to balance the force.
in a right hand twist, the axis will point to the right.
because the bullet is long, this will steer the bullet due to friction with the air to the right, a thing we refer to as spindrift. the longer the bullet the faster the twist required for stability, and hence the more spindrift.
this is not an issue, as we can calculate it and allow for it.
the second force on the bullet is drag, most of which comes from the nose of the bullet pushing through the air.
the major drag reducer is lengthening the ogive of the bullet.
using cast bullets limits ogive length, as what happens to noses when we fire the bullet will negate really long ogives due to setback, as well as potentially reducing accuracy if setback includes some movement of the centre of mass from the geometric axis of the bullet.
so we can maintain a longer ogive by using harder alloys, a work in progress by a number of people at the moment.
it clearly works as proven by relative drops reported by numerous shooter"s drop figures.
while drop is not an issue in itself, as sights can deal with that, reduced drop also indicates reduced wind deflection.
the thing we don't see is reduced nose drag comes with the centre of pressure in the bullet being further to the rear.
also within in the bullet is the centre of mass.
the distance between the centre of mass and the centre of pressure is called the overturning moment.
the longer this moment is, the more you have to spin the bullet to retain stability.
the centre of mass does not change, so by keeping the centre of pressure as far back as possible stability is helped.
there are other forces on flying bullets as well.
the main one is direction and strength of wind.
as we know, a wid from the right will make a rhtwist bullet shoot high.
this because the force it puts on the bullet makes the bullets axis point a little more upward, thus steering the bullet a little more upward.
(and vice versa for a lh wind).
after a certain distance of flight from the muzzle, these forces if they do not change come into balance, and the bullet will go into the yaw of repose, nose a bit above the line of flight, and a bit to the right.
now to put this into the real world.
firstly wind forces are never the same, and the longer the range the more chance of having a number of different wind forces on the bullet during flight.
i have even had a full change of direction during the approx 3 seconds of flight to 1000 yds.
apart from making the wind call for an extreme change null and void, the change of forces realigns the bullet axis, and slightly steering it somewhere else, thus enlarging the group.
in wind conditions we tend to notice this mostly in the form of vert.
going back to the force of drag.
a supersonic bullet has a fair bit of drag, which slowly increases to the beginning of transonic velocity.
during transonic speeds drag reduces rapidly, until the bottom of the transonic zone where the reduction ceases and then starts to slowly increase again.
during this process the centre of pressure moves forward slowly, back quite suddenly, and the quite suddenly stops that and moves forward again.
what this change of forces does to bullet axis alighnment we can only begin to imagine, but at the very least it put stability in a vulnerable position.
my own results from shooting at paper seem to suggest the worst place for this to happen is at the bottom end of transonic.
when i started experimenting with 40 cal pp bullets in a 13" twist, i thought a 1.55" bullet would be safely stable, and truth is i never got a dirt digger.
however i did get some not round holes at certain ranges.
successive bullet moulds by KAL made this go away at 1.5" long, and interestingly verticle was better as well.
so we need the least drag, not only to reduce wind deflection, but for better stability which equates to more long range accuracy.
this means the longest, heaviest bullet with the longest ogive.
translated into english this means hardest alloy you can use that will still bump into the rifling, longet and best shaped ogive, and of course the fastest twist you can run so that stability in at no stage in flight marginal.
that bit extra stability will be of great assistance when things get a bit western, as in say if there is a windshear at the bottom end of the transonic zone.
all these transonic issues can be moved closer to the target by increasing muzzle velocity.
they will have the same angle of divergence, but being nearer to the target this will result in smaller groups at the target.
a bit like it is more important to get the wind right at close range than further out.
bruce.
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desert deuce
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Re: drag, twist, and transonic flight.

Post by desert deuce » Mon Apr 19, 2021 6:27 pm

Correct on the 900 yard conundrum and one load for 800 & 1,000 and another for 900. I was not alone in that predicament.
That problem has been rectified, why it existed in the first place and what corrected it is still unresolved to my satisfaction.

By the definition of trans sonic the implication, (for bullets), is that the projectile must first start out super sonic before it can go sub sonic.

Another postulate of Dan's was that the bullet travels nose up in relation to the line of trajectory.

I do know that some bullet holes at 1,000 yards appear round in the target and some appear, (in exteme cases), more of a figure 8 and every once in a while give a little more than a figure eight and for sure did not bounce into the cardboard by striking anything before hitting the target. I have no explanation for any of these things seen on the target.

The youtube that Semtav shared: https://www.youtube.com/watch?v=lXODyVnE_Dw is quite interesting.

The point Dan and I belabored was when those sonic circles referred to in the youtube catch up with the front of the cone of disturbance and create the sonic boom why does one design bullet return to or remain more stable in path to target than do others? Or, why will one bullet perform better in the same load and rifle in poor conditions than another? Dan worked on nose shape, width of grooves and other factors along those lines theoretically and put those theories into practice and came up with different variations of the money bullet.

If I understood the gent in the video we three agree that the bullet's reaction to the conditions at the point it goes subsonic is key. Actually from the point the bullet goes subsonic until it strikes the target.

Giving that thought a boost, if the bullet is steered off course then the closer to the target this happens the less deviation from point of travel. Is this true deflection?

I don't use point of aim here mostly because that is where you intend the bullet to arrive at the target which is independent of what happens to the bullet path after the bullet leaves the barrel.

And yes here is the bad news, devining the conditions and working with them may seem like magic to some, BUT, the only way I know of to learn how to shoot well in poor conditions is to shoot in poor conditions. This is where theory meets reality.

As for the .38 Caliber Theory for long range......as far as I know that is still Theory.
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desert deuce
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Re: drag, twist, and transonic flight.

Post by desert deuce » Mon Apr 19, 2021 6:53 pm

I see Bruce and I were typing at the same time. 8)
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bruce m
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Re: drag, twist, and transonic flight.

Post by bruce m » Mon Apr 19, 2021 7:13 pm

zack,
how does your 900 load shoot at 1000?
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desert deuce
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Re: drag, twist, and transonic flight.

Post by desert deuce » Mon Apr 19, 2021 8:16 pm

As far as I can tell Bruce, the current load shoots well enough at all 3 ranges to not worry with further.
What I am struggling with now is which profile shoots best in less than optimal conditions and there is only one way to determine that.
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Re: drag, twist, and transonic flight.

Post by bruce m » Mon Apr 19, 2021 10:28 pm

interesting zack.
it is my belief that 1 bullet can do it all if it has the stability to not be disturbed by whatever forces affect it.
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Re: drag, twist, and transonic flight.

Post by bruce m » Mon Apr 19, 2021 10:42 pm

add to that, if it is good at 900, it might well be the best 1000 yd load as well.
however guy's experiences would be interesting here.
my own experience with not round bullet holes was more at 600 to 700 yds, after which the holes went back to being round again.
shortening the bullet in the same twist made it go away.
it seems that more guys are trying 16 twist 45 cal barrels these days, and few talk about going back to 18".
with regards 38 cal for long range.
if you compare a 38 cal 1.5" long bullet with a 45 cal 1.5" long, the 38 looks more streamlined .
this is because it has a higher fineness ratio, which means its length divided by its diameter is a bigger number.
however it will most likely have a lower b.c. as the formula for that comes in part from fineness ratio x weight, and the 45 cal has a lot more weight.
also the 45 cal has a greater radius, and therefore requires less twist for the same stability.
of course the same applies to 45 and 50 cal, but you would need a mighty 50 cal gun to shoot high b.c bullets with the charges required to achieve 1300 to 1400 fps with any precision in long strings.
perhaps the new long range benchrest bpcr discipline will allow for this.
at the moment 40 cal seems as small as is feasible for long range, all the above taken into account.
bruce.
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