Polygonal Rifling

Getting ready to order another barrel with .458" and .470" groove but this time 33" long with 20" twist. Thinking about a heptagonal cross section with roundly blunted vertices to minimize the amount of bullet expansion needed to seal the bore. So I put pencil to paper to figger the difference between the radius of what would be the .458" bore diameter and the vertices of the "grooves" for an ideal regular seven sided polygon versus limiting the groove diameter to .470". What I came up with was that from center point to the bore wall would be 0.229" (half of .458") and to the corners (vertices) would be 0.254"...
That is effectively a 25/1000ths "groove depth" and way much more than what you'd expect in "round ball rifling". So, holy mole', if I loaded with .457" diameter bullets in a perfect heptagonal bore they would exit the muzzle at dang near .51 caliber! I'd just never looked at it that way before.

And then I started thinking, hey, but wait a minute, what about people that shoot round bullets in their .451 caliber Whitworth rifles with hexagonal bores? How much expanding is going on in there?

So plugging in the numbers I came up with even larger amounts of expansion being needed due to the more sharply angled vertices in the hexagon. So this morning I got a new way of looking at muzzle loading rifles. And I'll stick with the idea of having bluntly rounded vertices on the hexagon.

nkbj said:

And then I started thinking, hey, but wait a minute, what about people that shoot round bullets in their .451 caliber Whitworth rifles with hexagonal bores? How much expanding is going on in there?

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It's been pretty well established that patched round ball does not obturate larger in the bore when fired. It has to do with the round surface of the sphere where the expanding gasses apply pressure.

LD

Loyalist Dave said:

It's been pretty well established that patched round ball does not obturate larger in the bore when fired. It has to do with the round surface of the sphere where the expanding gasses apply pressure.

LD

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Round bullets Dave.

nkbj said:

Round bullets Dave.

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Sorry,

You meant round nosed bullets..., I see that now

LD

Understood my friend.
You know, the part on the rifling thing that made me go wow was how much the round sized bullets are expanding to fill out the hexagonal bores in Whitworth's. It's darn near, well, just astounding. And reportedly people get sufficient accuracy for their needs. Bob Hoyt once told me that deep grooved barrels shoot long bullets just fine and at the time I thought something along the lines of uh, well yeah, but only if everything is just right, maybe...


That brief exercise in putting pencil to paper, figuring out how a hexagonal or heptagonal bore operates, gave me a somewhat different view.

nkbj said:

Understood my friend.
You know, the part on the rifling thing that made me go wow was how much the round sized bullets are expanding to fill out the hexagonal bores in Whitworth's. It's darn near, well, just astounding. And reportedly people get sufficient accuracy for their needs. Bob Hoyt once told me that deep grooved barrels shoot long bullets just fine and at the time I thought something along the lines of uh, well yeah, but only if everything is just right, maybe...

View attachment 354266
That brief exercise in putting pencil to paper, figuring out how a hexagonal or heptagonal bore operates, gave me a somewhat different view.

Click to expand...

WW sights have increments opposeing sides giveing H & C viz Hexagonal & Cylindrical . I have an old 490 cal with three deep grouves & a pitch of 1 in 30 clearly meant for a mechanically fitting projectile so I made just such a winged mould with a deep hollow nose center . It flew to greatly upset shapes fired in water and made serious mess on a deer . but it shot a patched round ball fine as well as the cylindrical bullets of various weights with no hollow nose even out to 500 yards on the range with a channelured bullet. the exterior of the twist barrel was /' Is so pitted with rust you still cant read the makers name But the bore had kept good (Same story with my old twenty four bore Two Grouve , good bore , rust streak exterior ) the 3 winged cost me a whole 3 pounds from Stan Share Scottish dealer who did Nottingham Arms fairs. The 2 grouve given me as the owner who believed Hans Busk the Victorian Writer who condemned the Govt Brunswick rifle and lauded the by then more advanced 1853 Enfield Expansive bullet & I tried conicals but the belted ball loaded easy & shot reliably flatter with its 1 in 60 '' pitch .Which is probably too academic as I doubt Any such rifles are made or offerered today .And the WW about as exotic as such systems go . I did stick together the double barrels of a Jacobs double infantry rifle same rust streak but bores still good just had the barrels sans rear sight but useing the ' mounts' of a Double Scinde Irregular Horse Jacobs smooth bore Swinburne carbines . So readily admitted the false breach so I stocked it up for a customer . How he got on I know not . But The Late De Witt Bailey had made extensive trials with John Bell and told me they found even good specimens shot worse that the Enfield issue rifle . . Hans Busks condemnation of the 1836 adopted two grouve belted ball Brunswick might not have had the developement of the 1850s Minie principal But it out shot the Baker rifle so hardly deserved Busks contempt for it . Of the Nepuali cache of so called ' Brunswicks' I cant begin to compare perhaps some might have been properly rifled but too many are so badly rifled they are unworthy of the name ( Charras is very cheap in Nepal ! )That much I know & might account for it .
Rudyard's rambling writing on Winged projectiles