How long a neck is too long?

bdyal1972

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I want to design a cartridge to minimize deterioration in the throat with high velocity monos... 5000 fps with 700 bc bullets?

In industrial use I would look at this problem as ways to MINIMIZE flame front with minimal taper, 20deg shoulder AND a neck 3 or 4 calibers long... moly coated bullets, cryo treated and high pressure temp coated barrels...

Would appreciate suggestions and thoughts and ideas....

5000 fps IS THE FRONTIER!!!
 
A long time ago someone postulated(I think Precision Shooting Mag) that 6PPC barrel life of ~3600rnds was due to it's flame point of 73.7% up the neck. But, there were enough problems with this to resolve it as fake science.
For one, competitive 6PPCs consistently demonstrate an accurate barrel life of under 900rnds. Second, there is no evidence that 'a flame point' exists at all in cartridges where great barrel lengths are needed to even burn all the slow powders. Third, nobody has since publicly expressed validated throat erosion changes with particular settings of flame point. Fourth, accurate barrel life is not bound by throat erosion, but carbon restrictions, and sometimes similar moly restrictions.

If you just want to test it, then I suggest you first design your cartridge in a highly improved state. This, to first keep most of the powder burn inside the chamber. Otherwise, if your powder is funneled down the bore as mass added to the bullet, burning with travel down the bore, then there is no flame point to begin.
Every cartridge with a 20deg shoulder does that. They are very inefficient.
You might consider Gibbs or Ackley cartridge improvements, but also with body length/diameter ratios as prescribed by the WSM patent 6,595,138. The gist of which: the length of the wide-body portion of the case should not exceed 3.33x the diameter of wide-body. The lower you get this number, the greater the % of powder actually burned in the chamber. The trick to this is large diameter cases need more barrel steel around them to mitigate pressure 'problems'.

Required neck length for 73.7% flame point might then be:
((CALdia/2)/(Tan(SHLDRdeg*PI()/180)))/0.737
I could email you a flame point spreadsheet.

I chose to build a 26wssm Imp to see for myself the virtues of that patent. My conclusion is that the patent claims are valid, as I did have to jack up QuickLoad's default efficiency (a lot) to match my results.
But as far as accurate barrel life, 3 barrels came in as predicted without consideration of flame point (which calcs at 58% up necks in this case). And I did not have much for throat erosion where accuracy was consistently lost.
Just the standard lake bed cracking, developing further & further down the bore, eventually scaling off here & there.
 
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I want to design a cartridge to minimize deterioration in the throat with high velocity monos... 5000 fps with 700 bc bullets?

In industrial use I would look at this problem as ways to MINIMIZE flame front with minimal taper, 20deg shoulder AND a neck 3 or 4 calibers long... moly coated bullets, cryo treated and high pressure temp coated barrels...

Would appreciate suggestions and thoughts and ideas....

5000 fps IS THE FRONTIER!!!

5000 FPS! I applaud this ambition.

You've got great advise regarding shoulder angles...

I must add my part and implore you to forget about moly (molybdenum disulphide) and go with hbn. (Hexagonal boron nitride).
 
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