Conventional vs. Polygonal rifling --- Advantages/Disadvantages

[JHT]

I wonder in lay-terms what are the differences between conventional and polygonal rifling?  I would imagine that each has its advantages and its disadvantages.  If so, what are they?  I'll bet the cost of production must come into play, correct assumption or not?  Where was polygonal rifling developed and when?  Do any U.S. custom builders use polygonal rifling in their builds?

Thanks,

JHT

[gunnut69]

I really don't know when it was invented but I've seen 18th century weapons with shaped bores, some even heart shaped.. I also have seen the Whitworth rifling pattern rifling where the bore is a series of twisted flats, like a octogon barrel twisted in a forge. The Whitworths biggest disadvantage was the bullets also have to be twisted as otherwise they couldn't be readily loaded from the muzzle. As far as manufacturing difficulties it wouldn't seem to be all that much trouble if using a hammer forging process... or even a broach.. It would be a bit of trouble if button rifling perhaps but not impossible to overcome.. As to problems with the form itself the worst seems to be an increase in area of the torqued surface. That is the surface area to shich rotational stresses are applied.. In the polygonal bore roughly half the bore surface is torq area. In a normally rifled bore only the sides of the bore are torqued. Also I have heard that there is less distubance to the projectile in a normally rifled bore.. I have not noticed a run on polygonally rifled barrels for any target sport..

[JHT]

gunnut69,

Thank you for your detailed explanation of the questions that I had put forth; in a format that even I was able to understand.


JHT