quote:

Originally posted by carpetman1:
Many years ago I was with a gent about a dozen years younger than me. We walked by a store front that had a Daisy Red Ryder BB gun in the front window. I mentioned that kids today don't know who Red Ryder was. He said "I don't know who he was". I bet there are many here that don't know. My point is in just a few years things fall by the wayside. Years ago, kids knew how to spin a top with a string. I bet there are many on this forum that have never done it. Perhaps they should learn and observe the action of the spinning top. People have theories about how the bullet behaves; even while in the barrel. Just theories, they can't climb into the barrel and observe. Back to the top, the harder thrown the faster it would spin. When the top hit, it would dance around, before settling in at one place. The faster it was spinning, usually, the more it would drift and dance. SOMETIMES a fast spinning top would quickly settle in. It would reach an rpm to where it settled down and remained stationary, then as it slowed it would start to wobble and again move. Keep in mind that this spinning top is going very slow in comparison to a bullet--almost as if stopped in comparison. Even an out of balance top would react the same way. You could cut grooves up and down the top and the grooves would make a buzzing noise. I whittled grooves in many a top and it was not done with precision. I also drilled holes in them and filled with molten lead to add weight---again a non precision operation. The point of the top (the part that made contact with the surface it was spinning on) was also altered--anything from a round shape to a very sharp point. All of these modifications, but the top would never just stay where it first hit and remain there, it would dance a round to varying degrees and the faster it was spun USUALLY meant the more it moved before settling down. I read that European barrels usually have left twist and thus the bullet drifts left and American barrels have right twist and drift right. Don't know why the difference--maybe because Europeans drive on the wrong side of the street--that may not be a factor. So the solution is simple. Put a Maytag twist in the barrel. The bullet starts off spinning one direction--then reverses like a washing machine paddle--when it exits it wont know if it is coming or going so it will be confused and not know whether to drift right or drift left and thus will remain on course, regardless of RPM.

quote:

Originally posted by 303Guy:
How many folks realize that spin stability is only slightly influenced by velocity - and then sometimes in the opposite direction, meaning that increasing velocity reduces stability. Not much mind you and only really becomes negative above 3000fps, depending on bullet shape.

It's the Europeans that drive on the right hand side and the Americans on the wrong side. Actually, some Europeans drive on the left too. Or is that Scandinavians?

Anyway, the spinning top analogy is a good one. Throwing technique made a difference. I could throw a top with a pretty high spin that would land and spin true straight away. Not so much when I was trying to peg another spinning top as we often did. Makes me think the same could be true of bullets being fired. After all, a 1-in-16 twist hornet is not supposed to stabilize a 60gr spire point bullet but it does and over a long distance.

In outer space the boolit would be tipped into a yaw that would not be able to dampen out as there is no atmosphere for the boolit to 'fly' in(and to cause drift, which requires gravity to cause an arced trajectory).

quote:

Originally posted by carpetman1:
I stated SmokinJoe is an old geezer. He did not confirm nor deny this. He would have done one or the other if it were not for senility.

quote:

Originally posted by 303Guy:
I'm just a kid! It's the beer that's kept me young.

The muzzle blast would tip the bullet and so would barrel vibrations. If bullet were launched in space with no disturbances and a very slow twist it should travel true, I'd think.

We only had tops in primary school. And marbles. Do kids ever play with marbles on the playground anymore?

quote:

Originally posted by 303Guy:
Because absolute perfection does not exist. Even if the base were perfect and the crown perfect, there would be small high frequency and perhaps large amplitude vibrations which would cause an imperfect impingement of the high velocity gas jet on the bullet base. It is said that there is a small acceleration of the bullet after it leaves the muzzle

Those same vibrations (think of audio range frequency) would impart the tiniest but quite fast tipping vibration into the bullet. From then on I can only speculate the effects because I don't know.

quote:

When dealing with smokeless, they both slip.......... Until you find what real accuracy is, you'll be making assumptions.

quote:

Originally posted by 303Guy:
Rest assured - there are no assumptions. One speculates and examines what evidence one can find and researches and listens to what others have found or speculated.

quote:

Originally posted by 303Guy:
I'm dabbling with toughening my alloy using copper which should theoretically produce a bullet that can handle higher pressure and spin and still hold together on impact in game. The stronger alloy should resist nose slump and base extrusion for a higher muzzle velocity. This is not about twist rate but bullet distortion in the bore.


This is what I mean. The base is undistorted and has no trailing edge feathering or extrusion. It also has about 99% weight retention. This is a fairly fast rifle bullet so that's mission accomplished. The base edge damage is from the nose folding right over into it. I pulled it off for examination.

Getting back to nose slump.


This was at a much lower velocity as can be seen by lack of impact damage in the same medium that caught the above bullet. This bullet is going to loose accuracy exponentially at higher velocities/spin. It's not the twist rate that's the problem but bullet distortion in the bore. This bullet also shows rifling skid (paper patch, remember).

So while the bullet base damage/distortion problem may be overcome, I still have to overcome the nose slump problem.

Most folks have no idea nose slump is occurring since the nose gets damaged on impact and can't be examined.

The top bullet also shows that there was no rifling skid but not whether there was patch slip. The lower pic shows no patch slip but one cannot be assumed the to be true at higher pressure.

So, I still have bit of playing around to do with alloy strength (not hardness) and bullet shape i.e. a shorter nose with a wide meplat to promote expansion and generally produce an effective wound channel.

quote:

Originally posted by 303Guy:
I should mention that I was using reject bullets for test tube firing. Slump can only be caused by the applied stress exceeding the yield stress of the alloy. The shank of the bullet is supported by the bore and the base by the gasses acting on it so only the nose slumps. However, one should remember that the nose is subject to far less stress than the base so for the nose to slump means there is a problem to be overcome.

I shouldn't think rifling skid through a patch would be greater on a smooth side than a grooved bullet, especially considering that grooved bullets usually have a bore-ride section which offers no driving surface. The driving bands on a grooved bulled is far smaller than a smooth side. What we are seeing on that example is the edge of the rifling land wearing into the patch, something that seems to happen if the rifling lands are a bit rough which was the case with the rifle this one was fired in.

But getting back to RPM thresholds, I'd suggesting that what is happening is that as the velocity is increased, the increased pressure induces greater nose slump, the effect of which is exacerbated by the higher RPM. I'm suggesting that a slower twist would be less sensitive to nose deformation than a faster twist.

quote:

Originally posted by 303Guy:
I made some updates while you were posting your reply!

I'm looking forward to his bullet trap results too.

It's true about damaged bullet noses but how much influence would bullet slump have as it distorts more of the bullet than a damaged soft point on a spitzer? Good point you raise there.

quote:

In many instances you can take a softer alloy with a paper patch and exceed the velocity of the same bullet made of your normal alloy that isn't patched. That kind of debunks the nose slump theory.

quote:

Tell me what you think nose slump is and how it happens.