Tipped match bullet length question.

[pondskipper]

I was wondering if when measuring a bullets overall length to determine the Miller stability if the polymer tip should be included in the measurement or not due to the extremely low amount of mass of the material the tip is made from in comparison to what the other materials in the bullet weigh. I do understand that the tip is very much so there and adds length but due to how little mass it actually adds to the bullet does it actually account for much of anything?

 

[Pdvdh]

There is a modified formula and Al or plastic tips do reduce the twist requirement.
And the hollow inside the jacket tip of match style bullets also reduces barrel twist rate requirement.
Google search should hit on the modified formula. Include the search words Michael Courtney.
Litz isn't fully in agreement last I asked about this. Others are.

 

[rlspahn]

Here's a link to Bryan Litz's thoughts regarding the modified formula proposed by Michael Courtney:
http://forum.snipershide.com/threads/debunking-courtneys-stability-myths.241591/

 

[pondskipper]

Well, it sort of gave an answer and sort of didn't, I do agree with Brian that the testing methods use were invalid because a bullets forward momentum vs it's rotational decay are by no means perportionate to each other, so just loading a round down to already near or below subsonic velocities and firing it won't yield the same results as firing one from a typical velocity and load out to extreme ranges, the one fired from a normal velocity will still be spinning far faster even after 2-3 seconds of flight time than one fired from a transonic/subsonic load out of the same twist barrel. But all this still doesn't technically answer the question, how much if any does the politer tip account for if any in determining a bullets overall length?

 

[Pdvdh]

I've read that Litz spat-based response to Courtney's work, and others on this Forum. There's been a multiple number of them. Litz and Courtney aren't friends, and that point comes thru loud & clear. Litz needs to grow up, in this regard.

I use Courtney's modified Miller formula. Suggest you do also. Of course it's your choice.

It mathematically models the answer to 'how much'. Isn't it somewhat intuitive that if the forward end of the bullet is really light (say light as the air in the atmosphere) that the barrel twist rate requirement would be reduced?

Lastly, how else could one project 'how much', without spending time and money testing over and over again. I'm going to be testing a 130gr Wildcat bullet in my 25 RUM. Miller formula predicts unstable in 10 twist. Courtney's modified Miller formula predicts stable. I have every expectation they'll be stabilized adequately due to Courtney's work AND because another member has already demonstrated stability in his 10-twist barrel.

Stability is determined without consideration of whether or not Litz likes Courtney! Hard to trust Litz when he let's his feelings affect the positions he expresses on external ballistics. I don't tune in to read Litz-authored soap operas.

 

[pondskipper]

Yeah I picked up on that.

 

[adam32]

Michael Courtney is about as smart as they come...

 

[gohring3006]

There is a modified formula and Al or plastic tips do reduce the twist requirement.
And the hollow inside the jacket tip of match style bullets also reduces barrel twist rate requirement.
Google search should hit on the modified formula. Include the search words Michael Courtney.
Litz isn't fully in agreement last I asked about this. Others are.

I agree, Michael worked hard on the Miller formula. He has lots of data on it. And would be happy to explain it. Too bad he was run off, over a thread that everyone involved including me, took to far.

 

[just country]

morning, I am not being a smart ***. what formula do the
US Marine and Army snipers use for ballistic formula's??
they r the very best at there work!! GBOT TUM

 

[WAMBO]

JBM has a calculator for stability that allows the addition of the plastic tip length when using tipped bullets.

 

[tankgijohn72]

The tip's minimal density compared to the lead won't do much to move the center of gravity of the projectile. But, the polymer tip will extend the distance between your center of pressure and center of mass increasing the moment arm that can cause instability. Either way it shouldn't drastically change the calculation. Also, its just a formula that has some amount of unknown to it. If your stability factor is close to 1.5 or lower, put holes in paper. They will tell you things the calculation won't.

 

[mwar77]

Good info

 

[Pdvdh]

Too bad he (Michael) was run off,...over a thread that everyone involved including me, took to far.

I took it to Michael's favor. There were, and remain, an abundance of Berger/Litz luvers. Michael spanked their bottom, and the Berger home team climbed aboard the Berger band wagon. Regardless, Eric and Bryan were an embarrassment to themselves, and the company they represent.

 

[gohring3006]

I took it to Michael's favor. There were, and remain, an abundance of Berger/Litz luvers. Michael spanked their bottom, and the Berger home team climbed aboard the Berger band wagon. Regardless, Eric and Bryan were an embarrassment to themselves, and the company they represent.

I agree, I was on Michaels side. But if my memory serves me, I think I engaged in some name calling and stooped to a level that is below my character. I still to this day, believe Michael got a raw deal from insignificant nonsense.
It left a bad taste in my mouth with Berger and applied ballistics.