rotational decay

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mdeland
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Re: rotational decay

Post by mdeland »

Thinking on it some I had forgotten about the bow wave moving off the nose of the bullet which is compressed air pressure that makes the air passing over the bullet shank de-laminate from it which would probably initially discourage the patch peeling off from the front by the slip stream.
I think we may have had a real utopia moment here to learn something neat thanks to Brent's video.
bruce m
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Re: rotational decay

Post by bruce m »

my confetti does not look anything like what is coming off that bullet.
it is more like strips.
if the bullet is not patched too far forward the cuts go right to the front.
in fact this is how you work out how far forward to patch the bullet for a hardness of alloy.
at the rear, some of the strips are joined to the base fold under.
I would not consider the confetti in the video as being what you should aim for.
strips cut fully to the front would be more likely to peel like a banana skin.
bruce.
ventum est amicus meus
mdeland
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Re: rotational decay

Post by mdeland »

Bruce, some years back I was curious as to how paper patching would cut if driven through a bore by hand so did just that. I drove a couple through a barrel and was surprised to find the paper not cut through cleanly when unwrapped from the bullet. It was heavily creased but not cut through. I reasoned that this was probably because driving a bullet through a barrel by hand lacked the speed and centrifugal force present when shot which probably is true but then again a lead bullet is continually being bumped up with each hammer blow driving it up bore so who knows which is harder on a patch while still in the bore.
I never ever considered that the patch was initially being stripped from the rear which I think the video clearly demonstrates. I completely forgot about the compressed high speed bore air which has to be evacuated before the bullet emerges. I'm quite sure now that is what is initially breaking up the patch.
Perentie
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Re: rotational decay

Post by Perentie »

I thought we were going to see if recoil and muzzle rise happened before the bullet made its exit but they must have had the rifle firmly clamped.
Good video. Thanks Brent
bruce m
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Re: rotational decay

Post by bruce m »

mike.
do not take that video as a good example of confetti manufacture.
the paper seems to be unwrapping more than cutting.
added to which we do not know what wads were used or the thickness of paper.
if the paper was too thick it cannot cut properly.
bruce.
ventum est amicus meus
mdeland
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Re: rotational decay

Post by mdeland »

It is clearly being stripped from the rear though not the front and is not the burning powder gas that is over taking the bullet in flight just before the patch comes apart. I don't see any other explanation but it is the high speed, compressed and heated, bore air that is breaking up the patch from the back side. This should give us more understanding to possibly improve patching methods and bullet design.
Kurt
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Re: rotational decay

Post by Kurt »

I shot yesterday in the rain and I collected some patch remnants to look at to see how it's shredding in the .44-77.
The rain dropped it straight down very close and I did not find and inner wraps. They were wrapped with .0018" thick 50% cotton Southworth paper.
IMG_3583.jpeg
The reason a dog has so many friends is because he wags his tail instead of his tongue.

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mdeland
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Re: rotational decay

Post by mdeland »

I sure love the look of PP cartridges! Looks like she shoots Kurt! I can read most of the target but couldn't make out if the range was printed on. Looks like a tuft of wind snuck up on you for one shot ! Good shooting! Are those wet or dry wrapped?
Kurt
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Re: rotational decay

Post by Kurt »

Mike it was only 136 yards and shooting off sand bags.
I mounted a new scope on the .44-77 Shiloh Farmer and shot here at home because the range is shut down.
Well you know that Henry the Gremlin always has to take at least one out of five to let you know he is still looking over your shoulder when you shoot. :)
The reason a dog has so many friends is because he wags his tail instead of his tongue.

"Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery"Winston Churchill
bruce m
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Re: rotational decay

Post by bruce m »

mike,
I am not arguing what happened in the video.
you can see that.
the point I am trying to make is that if my confetti looked like that, there would be no point in continuing with that ammo.
look at kurt's confetti.
it is completely different.
the video demonstrates gas well.
but as far as patch stripping, it is like taking a picture of a dead black bear with a 270 win rifle, and saying the rifle is excellent for the bears on Kodiak island.
people see the picture and believe it to be the norm.
bruce.
ventum est amicus meus
mdeland
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Re: rotational decay

Post by mdeland »

I believe you, I was more focused on and excited about learning something new about patch expulsion, cause and effect.
Kenny Wasserburger
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Re: rotational decay

Post by Kenny Wasserburger »

I am a firm believer in thin paper and shredded confetti at the muzzle, partial wraps mean the bullet did not upset evenly. That means shit accuracy. Talk about rotational decay.

I totally agree with Bruce btw. Zack mentions that my ammo is too pretty to shoot, he wasn’t kidding. And that voice was developed talking over a rig or plant noise. :P

The 16 twist does have more spin drift in theory, oddly enough the best scores for record at 1 mile all were fired with my Hell Bitch LRE 45-110 with a 1-18 twist barrel. I may try the 25# 16 twist 45-110 at the mile this year.

One’s time is best spent studying the conditions and their particular effect on ones choice of bullet and load combo. Maintaining vertical at 1000 yards is what I look for, and the addition of one or more grains of powder is easy with a 45-110 or a 45-100. This still allows the wad stack I have cultivated these last 25+ years to work exceptionally well. From 200 yards to 1 mile.

Honestly if you want a real time education in rotational decay be in the armored pit at my mile match, the bullets coming in, how they sound, is a lesson you can’t buy anywhere else.

Kenny Wasserburger
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Wyoming Territory Sharps Shooter
bruce m
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Re: rotational decay

Post by bruce m »

Kenny,
how much spidrift you have does not really matter, as long as you are zeroed to deal with it.
it will be interesting to read you impressions of the 16 twist after the 18 twist at 1 mile.
which ever is more accurate is your better friend.
and there are other factors that also relate to accuracy than twist.
yes it would be excellent to spend time in the armoured pit for many reasons.
bruce.
p.s.
interesting to note that zack finds pp ammo attractive.
ventum est amicus meus
mdeland
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Re: rotational decay

Post by mdeland »

That mile shooting would be absolutely fascinating to witness. Wonder what the 38-70 would do using Dan T's bullet he helped me put together. Need to see what it will do at 1K first before trying it at another 700 plus yards. The barrel is a 10 pitch Douglas.
Kurt
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Re: rotational decay

Post by Kurt »

I would be more concerned with yaw than spin drift. Spin drift can be corrected with the sights.
When you get the balance at the rear of the bullet wrong to the pressure point of the ogive and the centrifugal rotation decays you loose the gyroscope effect keeping the bullet in balance and you get yaw and that will turn into a tumble and also gets more wind drift and dirt diggers :) The longer the ogive the more rotation you need to keep the yaw down this also has the pitch effect. Spin it too fast and the bullet holds a nose up flight increasing the pressure point on the nose.
Before the longer nosed money bullets became popular the 18 twist .45's and the 16 twist .40 worked fine with the blunter nosed bullets and then came the sharper pointed ellipticals the call for a tighter twist barrel came around.
I wonder if the one or two twist less for elevation is worth the chances of a unbalanced bullet flight.
The reason a dog has so many friends is because he wags his tail instead of his tongue.

"Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery"Winston Churchill
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