more questions

[dg]

tony

mate

thanks for another informative response and a number of plausible scenarios.

I don't have the ballistic knowledge or access to proven facts to question any of your ideas or statements..

to my simple thought process, and until proven otherwise, could it also be plausible, that all vld the projectiles, due to whatever reasons, are to varying degrees oscillating or wobbling in flight.

despite these wobbles, the accuracy many are able to achieve with these vld projectiles, is simply outstanding !!!.

as best I could measure, on some bullet holes the pin hole offset is around 3/4 of a bullet hole in diameter, but in many cases the group in which these bullet holes occur is amazingly small at 1000 or 600 yds.

therefore, probably on the wrong track again, or right track (but caught the wrong train) could it be that for these wobbling projectiles, that if a pin hole is centred, it is a purely coincidental as the projectile hits the target at the mid point of it's oscillation to produce the centred pin hole ??

but regardless, I am inclined to think that if this partial instability is inherent in vld projectile design at the moment, then, if the clever people are able to make changes, to produce projectiles which eliminate or markedly reduce these wobbles, slight accuracy improvements might follow.

cheers
dave

[Tony Z]

Dave my knowledge on bullet flight is very limited.
But Houston we have a problem. Pin hole off set from my 636 are evident at 200 and 300 yards. They are also evident and still random at 600 yards. The problem is is that the offset is larger at 600 yards to what it is at the closer ranges. The theory says pitch and yaw tune out down range. My take on it is the "wobbly torpedo punt" becomes more wobbly down range. Which if you think about it makes more sense because as the spin rate decreases the precession becomes greater until the bullet destabilizes and keyholes. It is sounding more and more like Ellertson and co were right about bullets never going to sleep.

[Tony Z]

Well Dave we did ask. JR dropped this over this morning. Again a picture says a trillion words. No matter who you are there is no doubting the stability of a flat based bullet at long range and it dispells the notion that the paper or backer has some sort of influence on the hole shape. We use the same system today as we did ten years ago when this was shot. 187 BIB in a Bartlein 13.5 twist at probably one of our last ever Fly matches.

[dg]

mate

no one can argue with that !!!!!

certainly seems to be a message there.

it would be most interesting, if anyone can produce images of a target with similar pin hole orientations shot with VLD projectiles.

just for interest I thought I would roughly work out, the guessed angle of wobble for a typical 6mm vld 105 grain projectile

the typical overall length is around 1.250"

nominated .030" as a realistic and very conservative pin hole off sett.

assuming they are wobbling, and not knowing if they wobble around their centre or base these are the calculated angles of deviation from the axis.

for mid point wobble approx. = 2.7 degrees

for heel or base wobble approx = 1.37 degrees

either way, the facts are that the projectiles are .243" diameter and some pin hole off setts are more than .050".

something doesn't make sense here ???

precision rifles shoot to fractions of a minute of angle , not degrees .

could it be possible for the wobble to be really this much ?

maybe I am in error again ?

[justjeff]

Guys,

You are starting to sound like heretics here. Surely you both know that all you need to win is the highest BC possible. He with the mostest wins.

I think as target shooters we should be asking ourselves more focused questions like is BC that important? I personally am interested in the BC being high enough to allow the bullet to reach the target, and make a hole. Anything above that is secondary to having bullets that will group.

I will have to dig out my 0.985 at 600 target and check it. I think I shot it with 200 SMK, be interesting to see if the lower BC contributes to less point hole offset. I have some 185 D46 rebated bt Lapua arriving next week, I will run them alongside 187 BIB and see what I get.

Jeff

[Tony Z]

Well before you round up a mob brandishing pitch forks and torches Jeff , i reckon you should post up a pic of the 636 group you shot at 1K recently. The one around 5.xxx. Methinks it may have some serious random offset pin holes if memory serves.
The question still remains, what is the cause? As i said the other day, there is a lot of chatter about rebated boat tails.
We are not misplaced here at all. Bullet design is about to change drastically back to where it was 40 years or so ago. Tubb is marketing new rebated bullets and Gallant has launched their ULD 6.5 and 30 cal rebated boat tail bullets. Listen to what Tubb says. A bullet 50 thou longer and higher BC than the original 115 now stabilizes in an 8 twist. What i know and he isn't saying is that the rebated base shares the same launch characteristic as a flat base bullet. There is a youtube video of it where for the life of me i cannot find it. But i have seen it.

https://youtu.be/y9wVoztldsU

[justjeff]

Tony / Dave

I started going through old targets last nite. I have a great fly target, two hits on fly, 1" something group, shot with 200SMK, and guess what? The pin holes are all pretty much centre. I will pic and post it on the weekend. You are right about the 6mm, pin holes all over the place.
Interestingly, old targets for the 209 nevermind show pinhole dispersion, but only upwards, didn't see any in the lower hemisphere of the bullet splash. Makes me think they are trying to behave like a FB. Probably consistent with what you guys are theorising, given the short, 2mm boat tail.

I wait with interest to try the Lapua beside the BIB in the 13 twist, and then run some 200SMK as well. Might prove or disprove what we are thinking.

In the meantime, don't worry about me leading the mob with the pitchforks, all be right beside you running away from them too.

Jeff

[Old Trev-39]

Hi All,
I have some F/B 7mm. hunting pills and some of Anthony Finns 162 gr, rebated boat tails that I will load up and shoot at the 600 next week-end. Scores and groups could be shit, but who cares in the name of science.
Cheers,
Trevor.

[The Raven]

Wow I'm learning too much stuff! Very interesting stuff even if most of it flies over my head...

[Tony Z]

Raven, mate i appreciated your reference to the Blues Brothers and this thread. Great movie.

Why should it fly over anyones head though? The mathematics of it would do anyones head in. The mechanics of it show up on paper each and every match. All it is is a bullet point is marking center holes in the locations the mathematics say it shouldn't. The cause or rather the cure may unlock hidden BC and accuracy. Put simply, the nose of a bullet is tracing a circle and not spinning on its axis of symmetry. Depending where the point is during its flight, it shows up randomly on the target. VLDs seam to do it mostly. It is now known that there are degrees of stabilization where different twist rates result in different BCs which in my mind supports the notion that bullets never get to sleep and wobble their entire flight.
Flat base bullets rarely show this pin hole offset but if they do, it is usually because they are on the edge of destabilization. The video showing the two types of bullets leaving the muzzle show two different blast patterns. The boat tail looks like it may possibly get unsettled by overtaking gases. Flat base not so. A bullets wobble or pitch and yaw, are a given. But is it because of gas disruption or gyroscopic motion during transition from barrel to the atmosphere?
I firmly believe it's the gases fucking with the bullet which means there could be a cure. I also personally think this is all far simpler than what it's made out to be. I could be totally wrong but to me it appears to be an instance of not seeing the wood for the trees.
It's like stretcher tubes on barrels. There are lots of attempts to explain why they work (certain parameters) and just as many as to why they shouldn't. I take the Occam's Razor approach to it. It is a structural beam that locks the muzzle in a way so as to fix its location and free it from vibration.
With this, i see that the barrels are good. The bullets are good. The muzzles are good. Each launch motion is repetitive because you see good groups consistently which means one of two things. The launch is perfect and with current bullet technologies this is as good as it gets. Or, the error is repeated consistently and some combinations do it differently than others. But still a repeated error.

[dg]

gents

just noticed peter varley's record LG group target on the Virginia page.


http://www.virginia1000.com/aussie.page.htm

check out the pin holes

he shot this in Canberra

maybe this is a southern hemisphere thing ????

[The Raven]

Raven, mate i appreciated your reference to the Blues Brothers and this thread. Great movie.

Why should it fly over anyones head though? The mathematics of it would do anyones head in. The mechanics of it show up on paper each and every match. All it is is a bullet point is marking center holes in the locations the mathematics say it shouldn't. The cause or rather the cure may unlock hidden BC and accuracy. Put simply, the nose of a bullet is tracing a circle and not spinning on its axis of symmetry. Depending where the point is during its flight, it shows up randomly on the target. VLDs seam to do it mostly. It is now known that there are degrees of stabilization where different twist rates result in different BCs which in my mind supports the notion that bullets never get to sleep and wobble their entire flight.
Flat base bullets rarely show this pin hole offset but if they do, it is usually because they are on the edge of destabilization. The video showing the two types of bullets leaving the muzzle show two different blast patterns. The boat tail looks like it may possibly get unsettled by overtaking gases. Flat base not so. A bullets wobble or pitch and yaw, are a given. But is it because of gas disruption or gyroscopic motion during transition from barrel to the atmosphere?
I firmly believe it's the gases fucking with the bullet which means there could be a cure. I also personally think this is all far simpler than what it's made out to be. I could be totally wrong but to me it appears to be an instance of not seeing the wood for the trees.
It's like stretcher tubes on barrels. There are lots of attempts to explain why they work (certain parameters) and just as many as to why they shouldn't. I take the Occam's Razor approach to it. It is a structural beam that locks the muzzle in a way so as to fix its location and free it from vibration.
With this, i see that the barrels are good. The bullets are good. The muzzles are good. Each launch motion is repetitive because you see good groups consistently which means one of two things. The launch is perfect and with current bullet technologies this is as good as it gets. Or, the error is repeated consistently and some combinations do it differently than others. But still a repeated error.

It's not quite flying over my head but some of the technical concepts do. Hence why I resort to visualising in my head what is occurring.

While there are numerous factors to consider I would think the greatest potential negative is the transition from muzzle to air. The pressure is trying to get around the bullet and any disturbance to a clean flow could create issues. What's the chance the base of the bullet experiences a minor pressure reversal once the gasses behind the bullet drop off? Then there is the compressing column of air in front of the bullet (perhaps relatively minor) causing pressure on the front of the projectile and then suddenly dropping off as it exits the muzzle? Probably questions already pondered by people with more experience than me but it is interesting to contemplate the various interactions of forces.

[jacko-2]

man this thread gives me a head ache,, az i said in another thread,, i like what i see with a bit more twist ,,
the better the juenke numbers the better they look,, all so wind does have a affect on this,,really at the end az long az it shoots small , dont care what they look like,, cheers

[Camel]

Oh god, now Jacko is involved, thats really going to confuse things As if it wasn't already, well for me anyway.

[mick_762]

To paraphrase someone far smarter than I:


If a boat always points its bows to the current, why wouldnt a projectile to the wind?