Sub-Sonic Stability

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  • Last Post 27 November 2018
cove posted this 21 November 2018

In FS#253 page 11, Ric states that Accurate bullet 36-176P has "---a rounded edge to help sub-sonic stability".  I found this statement interesting since true wadcutters have mostly square noses, are loaded for sub-sonic velocities, and are stable/accurate at the distances they are normally shot.  Veral Smith's ogival wadcutter "was developed to allow stable flight at supersonic speeds".  I have been working with a 0.380 diameter wadcutter style bullet and wonder if rounding the nose a bit would help it, especially at distances of 50 yards and beyond.  Any suggestions as to where I can find more information on the subject?     

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RicinYakima posted this 21 November 2018

Cove, When I was investigating why full WC's became unstable at about 50 yards, I was lead to a website that was run by an aeronautical engineer. At sub-sonic velocities, the bullet begins to yaw and the forward sharp edge exaggerates this yaw to instability. The rounding of the front edge allows air spillage and does not accelerate the yaw. This was worked on in the 1930's for the nacelles of radial engine racing airplanes. WC's designed for target shooting were made to cut a clean round hole in the tagboard paper. That makes the highest score.  FWIW, Ric

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cove posted this 21 November 2018

 


Ric, that is the answer I was looking for.  I guess my next question would be: how much rounding of the nose is allowed before the bullet can no longer be called a wadcutter?  Thanks for the information - Cove     

 

 

 

 

 

 

 

 

 

 

 

 

 

 

r

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RicinYakima posted this 21 November 2018

I don't know that I am the one to be making up definitions or not. Lyman #35891 has a little button on the front to work with the airflow and is still called a WC. And #35887 and #358302 have rounded bumps and are still called WC. However #358271 and #358480 are called SWC's.

My most accurate .38 pistol bullets have about a 60% flat point and rounded / sloping nose to the top drive band. Ed Harris has made some excellent designs in the last few years for 38 S&W's that work well. You can search for his designs here on this site.

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Ed Harris posted this 22 November 2018

So you can look at them all, here are all of my Accurate designs for the .38 S&W and .38 Special:

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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cove posted this 23 November 2018

Ric and Ed: Thanks for the comeback.  I have been playing with shooting wadcutters in a black powder revolver and had Accurate #380158D made.  Trouble is, the rifling in in the Uberti 36 Remington is deep and I get a lot of finning.  I have been trying different groove and base designs by turning 380-158D in a lathe.  Come spring I will try cutting one in an effort to duplicate 36-176P.  I am in the process of writing up an article describing my efforts for FS.  Thanks again for the info-Cove

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Ed Harris posted this 25 November 2018

The rationale for the 0.03 bevel base on the 36-142H, 36-155D, 36-176P and 36-159H is to substantially reduce finning in +P .38 Special loads and eliminate it entirely in standard pressure .38 Special and .38 S&W loads when .359-.362" bullets in .38 S&W are extruded into .354-.355: groove diameter Colt barrels in my Colt Official Police and two Police Positives chambered in .38 New Police.

The bevel is obliterated by the time the bullets exit the barrels. Recovered bullets shot into water jugs show no finning, but a square base.  If soft alloy like 1 to 30 tin-lead is used in .38 Special +P loads over 900 fps, bases of recovered bullets are not perfectly flat, but show about 0.020-0.030 inch "cupping." This does not seem to impair accuracy.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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argie1891 posted this 26 November 2018

darn I always thought the function of the bevel base was to make bullets enter the case mouth without shaving lead. I have several moulds with a bevel base and they always seemed to shoot well. Several shooters have told me that they would pick up lube and be messy my experience has been that they easy to load and do not pick up lube on the base of the bullet. 

if you think you have it figured out then you just dont understand

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Ken Campbell Iowa posted this 26 November 2018

interesting that the bevel base prevents finning .... which a flat base can grow we think ...

yet at the end of the barrel, the base is flat ... so probably half way down the barrel the base is flat ...

why doesn't the flat base then grow fins??  it should only take a half inch of barrel travel compression to grow fins ... 

so maybe fins only grow in the high pressure first couple of inches of barrel travel ??  or only once when getting through the throat funnel ? or ::  do they actually ever fin ??

we need to water board these dang cast bullets, they don't willingly give out much information .

ken

 

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John Alexander posted this 26 November 2018

"yet at the end of the barrel, the base is flat ... so probably half way down the barrel the base is flat ...

why doesn't the flat base then grow fins??  it should only take a half inch of barrel travel compression to grow fins ... "

Ken, Seems to me that once the bullet is grooved in the first inch of travel the metal displacement should be over unless the rest of the travel widens the grooves already in the bullet. But the highest pressure/force/ and acceleration are all early.

I agree that spent bullets probably have a lot of information to tell us that we don't have because if it so darned hard to catch bullets without damaging them -- even harder for faster rifle bullets.

John

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Ken Campbell Iowa posted this 26 November 2018

ok, i can squint up my eyes see how that squishy base thing could happen ... my trouble is that i am a simplifyer ... usually the correct answer is the simplest one ...  usually ...

we humans have to remember that things happen the way they happen whether we understand things or not ... way too humbling ...

ken

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M3 Mitch posted this 27 November 2018

I will be one of probably several who will read that article, hoping to understand this phenomenon.  I know the thumb-rule is a 80% (approximately) bore diameter meplat (or smaller, or a round or pointed nose) will stay at least more or less point-on out past Fort Mudge, but I do know that full wadcutters shoot very accurately up to what is usually somewhat more than 50 yards, then they start tumbling.  I don't have a good intuitive grasp of this.  Have never done any experimenting on what all this depends on - velocity, twist rate, moon phase, what else?

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M3 Mitch posted this 27 November 2018

Cove, When I was investigating why full WC's became unstable at about 50 yards, I was lead to a website that was run by an aeronautical engineer. At sub-sonic velocities, the bullet begins to yaw and the forward sharp edge exaggerates this yaw to instability. The rounding of the front edge allows air spillage and does not accelerate the yaw. This was worked on in the 1930's for the nacelles of radial engine racing airplanes. WC's designed for target shooting were made to cut a clean round hole in the tagboard paper. That makes the highest score.  FWIW, Ric

 

Ric, do you still have a link to that AE website?  If so, please post it up here, I doubt I am the only one who would like to read it.

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RicinYakima posted this 27 November 2018

Mitch,

I wrote that article prior to 9/11. Old references from ten computers, including one lighting strike, ago? Not going to happen. Glen Fryxell wrote an excellent article on the " Los angles silhouette club" page about wadcutters. The reference concerned the NAC discussion of nacelle design and I believe it was in about 1935 or 1936.

Like everyone else who was writing in the 1990's, we thought we could save "links" electronically. There was nothing to lose right? No only did I lose hundreds of pages of my material, I lost all reference when lighting hit the power pole behind my house and my computer and three linked hard drives turned to smoke.

If it is not written down on paper, or printed on paper, and filed, it is nothing. Electricity is a passing fad.

Ric

 

 

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M3 Mitch posted this 27 November 2018

Thanks, Ric, I will read what Glen wrote, his website is a real resource.  He used to work here at the Lab, I have met him a few times, although I didn't realize he was a gun guru at the time.  I thought he was just a (rather high level) chemistry guru.

When I have some time to goof around, I can maybe do some Google searches to find that old AE article.  It's probably still out there somewhere, just a question of coming up with the right search string. 

I do agree that it's best to have a hard copy of any important reference.  Filing is also important unless you are willing to deal with an "access time" in days or weeks - sez me, the champion clutterbuck...

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RicinYakima posted this 27 November 2018

If I remember correctly, there was some discussion on the crashes at the Cleveland Air Races and if the nacelle design was a factor. (Conclusion was too much engine and too little airframe!)

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