rotational decay

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BFD
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Re: rotational decay

Post by BFD »

VectorMan wrote: Thu Mar 26, 2020 5:28 am
bruce m wrote: Wed Mar 25, 2020 9:10 pm 50 cal is king of the mentioned heap, but kicks too much in all but a very heavy rifle.
bruce.
What twist would be necessary for 1000 yard target competition in a heavy 50-90 rifle?
22" I think. don't hold me to it though. It would be the ultimate 1000 yd rifle - if it weighed about 25#
VectorMan
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Location: NW Missouri

Re: rotational decay

Post by VectorMan »

BFD wrote: Thu Mar 26, 2020 6:36 am
VectorMan wrote: Thu Mar 26, 2020 5:28 am
bruce m wrote: Wed Mar 25, 2020 9:10 pm 50 cal is king of the mentioned heap, but kicks too much in all but a very heavy rifle.
bruce.
What twist would be necessary for 1000 yard target competition in a heavy 50-90 rifle?
22" I think. don't hold me to it though. It would be the ultimate 1000 yd rifle - if it weighed about 25#
We shall see Brent, we shall see.
"keep adding powder til it bloodies your nose and blacks your eyes, then back it off bout 5 grains."
Kurt
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Re: rotational decay

Post by Kurt »

The 1/22 twist will do the job with a 700 grain bullet for long range if you do your job controlling the torque and recoil.

I quit shooting my 13# .50-2.5 when all the tool and washboard reamer marks where were shot smooth as high quality optic lens glass. :) But I been thinking about pulling it back out for the long range matches again.

My .50 is the only rifle the muzzle blast has polished all the bluing off the face of the muzzle and the whole rifle looks well used. :)
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
Longrange
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Re: rotational decay

Post by Longrange »

VectorMan, 22twist .5ocal=1.461" bullet. Max weight for length. Better off with a 25 or 26 twist less recoil. Vic.
VectorMan
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Re: rotational decay

Post by VectorMan »

So a 24 twist wouldn’t be bad then?

Thx
KA
"keep adding powder til it bloodies your nose and blacks your eyes, then back it off bout 5 grains."
bruce m
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Re: rotational decay

Post by bruce m »

what twist barrels are easily available?
faster twist will stabilize a longer bullet, which if cleverly designed will have a higher b,c, hence less wind deflection.
if 22 is available, go for that.
to maximize benefit, be prepared to experiment with bullet length until you go too far.
one factor that helps b.c. is length of ogive, the longer the better.
cast bullets are limited in this area, due to noses bumping up.
this brings to mind what the slug gun guys of friendship do.
they swage together 2 parts of a bullet, the ogive being a very hard alloy which cannot bump up, and the shank being in some cases pure lead.
I recall reading a story of doc pardee shooting slug guns in the 1800s.
some of those guns were so heavy as to require a paid loader in order to avoid exhaustion by the shooter.
guns at friendship were lifted to and from their rests into the loading position by machines like a crane for the same reason.
I believe some of the friendship guns were in the 0.7" calibre category, the action looking like a pimple on the pumpkin of a barrel.
others go for 40 cal, and anything in between.
the 50/2.5" case would be interesting droptubed full of powder behind a breech seated 2 alloy pp bullet.
should you wonder about the need for more powder, you could experiment by muzzle loading the rifle on a primed case to whatever charge you wanted to try.
this might indicate that the 2 3/4" case would be desireable.
if brent does 50 cal it will be interesting to follow the journey.
bruce.
ventum est amicus meus
bruce m
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Re: rotational decay

Post by bruce m »

the only point in shooting a 50 cal at long range targets is to beat a 45 cal.
compromise on b.c. in the 50 cal and you are just wasting time and money.
as well as a LOT of lead and powder.
bruce.
ventum est amicus meus
Kurt
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Re: rotational decay

Post by Kurt »

bruce m wrote: Wed Mar 25, 2020 8:26 pm ah the old fire your sighters and a change happens syndrome.
who can you turn to at a time like that?
far better to get 2 sighters in on the 2 extremes if you can, but that is not always possible.
now to precession and nutation, particularly in relation to wind shear and spindrift.
any bullet fired from a rifled barrel spinning undergoes precession.
what this means is that while the axis of the bullet at its base is stable, the nose is going in circles around the axis.
as the bullet flies, the circles become smaller and smaller, until they all but disappear.
however it is not quite that simple due to nutation.
nutation is the nose of the bullet going in smaller circles around to circle described by precession.
the line described looks a little like a multi leaved clover.
at the end, usually about 200 yds of flight, nutation disappears altogether, and precession is virtually non existent.
this is the point at which we say the bullet has gone to sleep.
it is why many want to test loads at 200.
fclass guys are now starting to test at 220 to be sure.
the faster the twist, the greater time of flight for a bullet to go to sleep.
benchrest shooters use slow twists and short bullets for this reason at 100 and 200 yds, and it is possibly why slow twist 40s are good at mid range.
but we long range shooters need longer bullets and faster twists.
when the bullet goes to sleep, all the forces on it, drag, gravity, etc are in balance.
these forces cause the axis of the bullet to settle into a position pointing above the arc of flight, and to the right of it for a r.h. twist.
the faster the twist, the greater is this angle.
because it is at an angle to line of flight it is described as yawing, and because it is asleep, it is the yaw of repose.
the angle it is at in relation to line of flight is called the angle of attack.
the lower the angle of attack, the less drag, because there is less frontal area.
the yaw if repose has a tendancy to steer the bullet, and thus a flying bullet will not hit the ground as soon as if it were just dropped, because it is steering itself upward a little, being nose high.
it will also steer a little to the right (again for a r.h. twist).
this steering is called spindrift, and the faster the twist, the greater the angle of attack, and therefore the greater the spindrift.
this can be calculated mathematically.
Kenny's 16 twist will have a little more spindrift than my 18 twist 45, as does my 13 twist 40 cal.
what is going on to a bullet during precession and nutation will make it very susceptible to any disruption, as another force suddenly comes into the equation that is not yet calculated.
this is partly why we fear problems at closer ranges more than long.
strong windshear in this period of flight will upset not just the yaw of repose, but precession and nutation which must be gone through to achieve yaw of repose.
during precession and nutation, the bullet is actually travelling in a minor corkscrew rather than an arc, purely because it is steering itself that way.
getting back to dan theodore.
when he was around, we long range shooters did not have to think about much, because he helped us.
one of my inspirations for pp shooting was Kenny w.
he never made any secret of failures, and kept hanging on for grim death to achieve his goal.
I recall him talking about finding one of his fired bullets in the carpark.
dan helped him and he gave dan credit.
now he shoots seriously good waterlines like palma shooter would hope for.
by the time I started pp, the new breed of pioneers had made it easy for me.
brent was another one. and there were others too.
not only was it the what to do, but more so the results achieved that inspire.
bruce.

Bruce,

I think a lot of the warble starts as the bullet clears the muzzle from the gases pushing it. I have studied a lot of super slow motion videos and it's clear to me what I see is the gases showing up before the entire bullet clears the muzzle. This can't be good for stability throwing the bullet slightly out of it's axis at the very start till the centrifugal spin gets it back in straight flight, you call it going back to sleep.

I have a rifle with a 34" long barrel I been planing cutting off 4" but before I do I think I will will clamp it up in the mill and port it with a series of small holes on the top octagon flats both sides. I been wondering what the effect would be to relieve the pressure behind the bullet before it clears the muzzle to eliminate the wobble that can start with an uneven gas leak as the bullet clears the muzzle. The velocity loss would be minimal with the last 3" of the barrel anyway but I feel that the bullet would be more stable as it clears the muzzle with out the blast of gas effecting the base with pout going many yards down range first.

Nothing will be lost except maybe some powder and shot giving this a try. It will still be cut off anyway if it makes no difference in accuracy. It will eliminate some of the muzzle jump if nothing else. :)
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
mdeland
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Re: rotational decay

Post by mdeland »

In my opinion Bruce, the 45 caliber cartridges in about anything has always sort of been an equilibrium diameter from the advent of the .45 Colt to the 45-70 and longer. It just strikes a good balance of power, cross section, stability,recoil and gun weight. Even in colonial days before the masses crossed the "Big Muddy" most of the rifled guns made by Americans were in the 36-45 caliber range. It could get the job done for every thing East of the Mississippi and still be a pretty good conservator of lead and powder. I have two patched ball muzzle loading match rifles in .45 cal.
One can comfortably handle large bore muzzle loading shoulder arms using patched balls but with cartridge ammo shooting high BC bullets for long range, the 50 cal just goes over the practical balance point of weight and recoil for most shoulder fired weapons.
Earlier this year I was shooting about eight benches down from a guy using a muzzle braked BMG round, bolt gun and the muzzle blast concussion would knock the ears off a brass monkey, as Jack O'Connor used to say! Even with the muzzle brake it was jerking the shooter around like a rag doll.
bruce m
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Re: rotational decay

Post by bruce m »

kurt,
yes the gas pressure on top of what I said.
when you look at it the poor bullet does not have much going for it.
please keep us in touch with the ports, good or bad.
you might need to keep the ports cleaned each shot to get a consistent result.
you are another that inspired me in the past, and continue to do so.
bruce.
ventum est amicus meus
bruce m
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Re: rotational decay

Post by bruce m »

mike,
possibly 42 to 45 cals became popular due to military use.
they demanded something that could deactivate horses reliably.
interestingly in those days 45 cal was thought of as "the new smallbore"
50 cal and bigger with round balls could not match the 45 with conical.
bruce.
ventum est amicus meus
mdeland
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Re: rotational decay

Post by mdeland »

I've seen slow-mo pictures of gas escaping ahead of the projectile too but I'm not sure that is powder gas. The bullet has to push a bore full of air out of it's way before exit and that air has some humidity in it. My guess is what is viewed may be steam from the compressed air evacuating the bore ahead of the bullet.
The reason I suspect this may be true is from Manns writing of how the powder at the front of the column, at the base of the bullet,which is nothing bore than a wad until it ignites, is well up bore and after bullet obturation before it burns up.
mdeland
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Re: rotational decay

Post by mdeland »

It could also be bore or bullet lube vaporizing in the evacuating compressed air column.
mdeland
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Re: rotational decay

Post by mdeland »

After the Civil war, the rifled .58 cal muskets were converted down ward in caliber from. 58 to 52 to 50 and finally 45 . This was the reason for trap door Springfields. Then with the advent of smokeless powder the dawn of the small bore came into practicality.
bruce m
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Re: rotational decay

Post by bruce m »

either was, gas behind the bullet overtakes and passes the bullet just after it leaves the muzzle.
bruce.
ventum est amicus meus
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