Stabilizing a bullet

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Coltsmoke
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Re: Stabilizing a bullet

Post by Coltsmoke »

Is there a standard or formula to determine how long the nose should be on a bullet? Is it a certain percentage of the OAL of the bullet? Is it about trying to keep the center of gravity as close as possible to the center of the bullet? Is there a reason Paul Jones cut the point of the Money Bullet bigger than BA does?
Normal isn't coming back, but Jesus is.
Coltsmoke
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Re: Stabilizing a bullet

Post by Coltsmoke »

Normal isn't coming back, but Jesus is.
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desert deuce
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Re: Stabilizing a bullet

Post by desert deuce »

Harkening back to extensive and numerous conversations that Dan T and I had about this subject, in person, on the phone and at matches.
(Not to mention match experience as a rifleman and/or a spotter for/with some very good shooters.)
In the end we accepted that "PROBABLY" the point in flight at which one of our BP bullets was most susceptible to destabilization by outside forces was at the transition from super sonic to sub sonic. Destabilization and deflection being two different subjects. One can adjust for observed deflecting forces, (steady 3 mph 9 o'clock wind), not so much for unseen destabilizing forces, (60 mph vortex down draft), which none of our bullets will survive.
The question then becomes "WHERE" in the arc flight of the bullet does this occur & what are the environmental conditions at that time & location? Understanding that conditions may change by the time you fire the next shot.
Accepting that we were dealing with two variables, one was conditions affecting the true flight of the bullet, deflection, and conditions serious enough to destabilize the bullet for the rest of flight until reaching the target if not falling short as from a vortex. In the latter case the variable was the ability of a certain bullet in flight to either resist destabilization altogether or return to stable flight after being marginally destabilized, "ACCEPTING" that once any bullet is destabilized to a certain threshold it can't return to a stable flight. In the pits this may sound like anything from a mad Hornet or the tail rotor on a Huey and that bullet usually avoids contact with the intended target. From a vortex maybe a gravel shower in the pits.
The problem then becomes, how do you adjust for conditions that you cannot see, as in above or between the flags? Usually, the only indication you have that something changed was your last shot. There are conditions wherein you calculate for and shoot for the X & 10 Ring, other times you raise a fervent prayer asking for each record shot to strike your target somewhere.

This is where that age old leveling consideration of reality comes into play. A little hint, you have no control over the conditions. Soooo, what do you have control over? AND, isn't how to deal with reality on the firing line more important than any other consideration? Moreover, what better place to gain this experience than at a match?
Sometimes you get the chicken, and sometimes you get the feathers!
mdeland
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Re: Stabilizing a bullet

Post by mdeland »

Thanks Coltsmokes, that was good stuff from Bruce M. on the subject !
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Distant Thunder
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Re: Stabilizing a bullet

Post by Distant Thunder »

Coltsmoke,

Thank you for that link, that was a good discussion. If someone is looking for the formula to design the best possible long range They will find it in that old thread. Might require a bit of sifting and a little knowledge base, but it's in there.

As for the original Ideal Postell it is my understanding that it was actually a grease groove version of the Sharps LR paper patch bullet. It was later modified to be more like the very successful Paul Jones Creedmoor design. As to the angle it had from the driving bands to the ogive on the original design I have noticed that the original Sharp LR paper patch bullet had a slight angle running from the full shank diameter to the start of the ogive also.

Bruce also mentioned, in the linked thread, Metford's design. I have been working with a bullet in my .44 - 2 1/4" that is as close to Metford's bullet as I could find, at least really available. In researching his design in .45 caliber it seems he also had an angle between the shank and the actual start of the ogive. The angle on the Sharps bullet was .250" long and amounted to .004" on the diameter. On Metford's bullet the angle was .150" long and amounted to .010" on the diameter. Since both bullets were patched over the angle and up to or nearly to the start of the ogive I assume the angle was considered part of the shank and not part of the ogive and was expected to bump up to groove diameter. I'm guessing that the purpose of the angle was to reduce the patch diameter at the leading edge to prevent any damage to it while chambering the cartridge.

Taking a look at just the ogive (nose) length on the two designs, the nose on the Sharps bullet was 40.7% of the OAL and the Metford was 43% of the OAL. The OAL of both bullets (.45 caliber) was 1.500" and both had a cup bases.

The radius at the tip of the nose on each was, Sharps - .125" and Metford - .135" So when you compare these two old designs to today's Money bullet they had shorter more blunt noses.

As to the 1.500" length I have no clue how they were able to stabilize those bullets in the slower twist rates in use back then. Maybe the cup base design aided stability, in effect shortening the OAL? The cup base would move the center of mass forward which would help also.

Shooting with an 18-twist .45 caliber today you would be right at the edge of maximum length for stability if you drive the bullet at 1400 FPS. That requires about 100 grains of Swiss 1 1/2 or more. There are a few of us who are having good results with paper patch in .45-70 running them at 1300 fps, but the length is best kept at or a bit below 1.450". I like 1.440".

If your going to shoot a 1.500" long bullet in a 2.1" case you really need a 16-twist and then you could actually even go a good bit longer.

My suggestion for those looking to design a .45 caliber long range bullet that will shoot well and remain stable in some pretty nasty winds is this; keep the OAL of the bullet to about .020-.030" short of what the calculators say your twist rate will stabilize, keep the nose length to between 40 & 45% of the OAL and the tip radius between .125 and .150". Stay with the flat base design, cast it with 16-1 alloy and patch it with the best paper you can buy :D . Adjust the other million or so variables until you get the best performance you can.

Pretty easy really!


YMMV
Jim Kluskens
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desert deuce
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Re: Stabilizing a bullet

Post by desert deuce »

FWIW, the original Ideal Postel 456132 has a beveled base. The original sample I examined the beveled base band was .456" in diameter and the next band forward was .458" in diameter cast from 1-16.
Sometimes you get the chicken, and sometimes you get the feathers!
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Distant Thunder
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Re: Stabilizing a bullet

Post by Distant Thunder »

You are correct there, DD, a bevel base it was. I was not aware that the base band was undersize? And clearly the number later changed to 457132.

I have a rather old Lyman reloading manual that shows some "Ideal Cast Bullet Designs". It does not list the 456132 or 457132. It does show the 457125 at 500 grains and it clearly wears a bevel base.

The old "Lyman Cast Bullet Handbook" (1973) I have does show a 457132 and it clearly has the bevel base and is listed in 3 weights, 415, 475 & 535. The 457125 does not have a bevel base in that book.

I find the old designs fascinating to look at.
Jim Kluskens
aka Distant Thunder
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