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I really cannot tell you how they patterned. Both were high grade collector guns and I or the new owners never shot them. Too bad, as the performance question is fun to think about.

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I'm sure we've had some June 15 1893 Horatio F. Phillips patent Vena Contracta threads but couldn't find them
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA181&lpg

From From Atkin Grant & Lang website
After the move to 10 Pall Mall in 1890, Joseph Lang brought out the Vena Contracta gun, the brainchild of Horatio Phillips (shooting editor of The Field magazine), which fired a 12 bore cartridge in a barrel which was contracted to a 20 bore gauge during the first third of its length. However it was not a great success, as the weight advantage gained was offset by increased recoil and indifferent performance and many of these guns were subsequently re-barrelled.

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RWTF - Are you saying your Aubrey has choke that have a continuous taper from front of the forcing cone to the muzzle? How are the barrels marked for choke? Have you measured bore and minimum at muzzle?

DDA

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Here are the Tapered Bore measurements from 2 Lefever crossbolt guns.

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]

Last edited by Daryl Hallquist; 10/15/21 11:59 AM.
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Daryl, I appreciate you taking the time to provide those Crossbolt Lefever bore measurements. I saved both for future reference.

It is interesting to see that the measurements do not indicate a continuous straight taper all the way to the muzzles, but rather utilize a relatively straight taper for most of the length, and then have a greater angle of taper for the last couple inches. This would seem to indicate that Dan Lefever was aware that a continuous straight taper was not as efficient, as noted earlier by Rocketman.

I never really doubted Dan Lefever's words when he said he had used a tapered bore system, because he was always an innovator. And tapered reamers are certainly nothing new. But of the relatively few Syracuse sideplate Lefever guns I had checked, all seemed to have a straight bore from the end of the forcing cone to the beginning of a roughly 2/12 to 4 inch tapered choke at the muzzle end. Bores in 12 gauge guns were typically around .729" to .731" diameter. Some were checked with a Stan Baker bore gauge, and a few were checked with plug gauges in the course of removing barrel dents. The guns I had checked that appeared to have had barrels shortened by 2 inches or more had very little or no choke remaining.

I had carefully checked the bore diameter of an H Grade I bought that was advertised as a 12 gauge. It turned out to be a 10 gauge, and it is the only 10 gauge H Grade Lefever I know of. It has the Twist barrels commonly found on H Grades. It too has a straight bore with a conventional choke taper. As I recall, the bores were around .770" and the muzzles were about .745" and .755" diameter.

I only have two crossbolt D.M. Lefever guns, an O Excelsior Grade and one unmarked that is equal to 8E Grade guns. I hope to soon find the time to check both of them to see if they also utilized the tapered bore system. And it would be interesting to know if there are any Syracuse sideplate guns that have this tapered bore system, since Dan Lefever was still at LAC in Syracuse when he made those claims.


A true sign of mental illness is any gun owner who would vote for an Anti-Gunner like Joe Biden.

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Thank you, Daryl. It appears from your measurements that there was no choke effect happening until 2" before the muzzle. Tapered bore to be sure but, as I understand it, that was not adding to any choke that was achieved in the last 2", where the real rapid constriction occurred.

Perhaps Don could enlighten us further on fluid dynamics and how the tapering bore, entering the 2" choke area, would affect the shot. For one thing, was there any increase in velocity in the previous 24 inches ( Optimus barrels) before entering the rapid constriction area, or were the decreasing pressures, bore wall drag, and "headwind" caused by the shot column having to push air out of the bores ahead of it causing enough negative effects that any velocity gain from the tapering bore would be a net loss?


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That there is rOcket science....

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Originally Posted by HomelessjOe
That there is rOcket science....

More like surgery.


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it is not my intention to side track this thread, but Daryl's measurements give rise to a question....i purchased my first Lefever gun earlier this year and was surprised to find that the bores both measure .750 (consistently, there is no taper)....i had assumed that to indicate that a good deal of honing had occurred somewhere in the life of the gun (1890 dom). but now i see Lefevers mentioned with bores in that neighborhood....were these high grade collector guns also honed, or were Lefevers subject to be found with oversize bores?

best regards,
tom


"it's a poor sort of memory that only works backwards."
lewis carroll, Alice in Wonderland
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Somewhere I read a quote from a Remington lab report circa 1930 that dealt with velocity increase as choke increased. The report noted slightly increased velocity with each increase in choke (I recall 50 fps for full choke). I hope someone knows the article I'm referring to as I have been unable to find it in recent years. That is what theory predicts, although said theory doesn't address a semifluid such as shot. The increase in velocity comes via reducing pressure over the length of the choke section.

Following is my personal theory as to how choke works (neither proven nor disproven). The mass flow rate from chamber through muzzle exit must be constant. The exit velocity is the sum of velocity at choke entrance plus velocity gained within the choke. Shot column internal pressure at choke exit is choke entrance pressure minus pressure lost across the choke length. Shot pellets at choke exit experience two forces acting on them that cause pattern formation. The pellets all have some deformation from contact with neighboring pellets (lead has a low spring constant, but does have ability to rebound from small deformation). Any of said deformation that is not permanent will return toward spherical and impart some small velocity to the pellets. The part of that velocity that is "sideways" will tend to move the pellet off the center line of the pattern. Likewise, there is pressurized air entrained within the shot column. At muzzle exit the air exits the shot column, some "sideways." This sideways air movement farther "blows" the pellets off the centerline. Thus, most every piece of shot has some sideways velocity.

A pellet that is one foot off centerline (outer fringe of a 24" pattern) at one tenth of a second of flight had a sideways velocity of 10 fps. That is on the order of 1/100 (0.01) of the forward velocity. Seems to me to be a reasonable amount.

The full taper bore would lose most of its choke effect due to friction loss from chamber to muzzle. If you tack a choke taper at the muzzle --- well, what is the point of the taper bore?

Keep in mind that shot pellet transit of the choke is an orderly event. Pellets do not "slam" into the choke. They flow through it.

DDA

Last edited by Rocketman; 10/16/21 11:11 PM.
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