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#604404 10/09/21 04:27 PM
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I am trying to get s better understanding of the process of creating choke in a new barrel. Not that I will ever have the skill, machinery or need to do it but I would just like to find out more about the process. Thanks! Gil


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Are you talking about “jug” choking a barrel?

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Gil and anybody else: Send me an email drewhausemd@yahoo.com and I'll send you "Making Double Shotgun Barrels" by A.P. Curtis in the November 1937 American Rifleman

Please let us know if you figure out how the fellas at Meriden Firearms did this with the "choke bored on the taper system"!! wink
1908 Sears, Roebuck & Co., Chicago, Ill. Catalogue No. 117:
"Shooting qualities- As before explained, the shooting qualities of these guns are unequaled for long distance killing, long range shooting, for penetration, pattern or target. Both barrels are full choke bore, so firmly constructed that unlike other guns, there is no recoil or kicking. That which in other guns goes into recoil in the A J Aubrey gun goes to give greater force to the shot."

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And now we know why the Sears & Sawbuck catalog was so popular in outhouses. It was already full of it ;-)


Caution: Hunting and fishing stories told here. Protective footgear may be required.
eeb #604421 10/09/21 09:55 PM
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No,eeb.

Last edited by gil russell; 10/10/21 08:37 AM.

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Ever read a Herter's catalog? If fish knew that you had their "special" lures they would jump into the boat to save you time and so they could get a better look at the lures in your tackle box. Hype drew interest and kids of all ages loved the hype.

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In the science of fluid flow it is well known that a constriction in the flow channel will cause an increase in velocity of the fluid and a decrease in pressure. Constant mass flow rate requires that the flow go faster in a smaller area. Velocity times pressure is a constant, so increased velocity requires reduced pressure.

A simple conical constriction is completely satisfactory for choking lead shot. Conical is an easy shape for a reamer. The barrel is bored so as to leave a little extra "meat" in the choke area. The reamer guides off the bore. There are myriad "secret/magic" reamer profiles. After reaming, the whole "she-bang" is lapped and polished.

DDA

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Say it ain't so Don - 'ya mean there is no magic!?! wink

What about the Herb Orre choke?

[Linked Image from photos.smugmug.com]

And the "Multiplied Choke Bore System"?
https://members.boardhost.com/lcsmith/msg/1624920858.html

Gough Thomas, Shotguns & Cartridges For Game And Clays, 1970
"Occasionally, a clay pigeon shooter's outstanding success at some major international competition will be attributed by him or others to some marvellous new system of boring. This is a subject that is in every way likely to involve elements that have nothing to do with practical ballistics; and in view of the fact that every conceivable variation in the boring of shotguns - every possible combination of features - appears to have been tried, one is entitled to treat any such accounts with reserve.”

Previous choke length thread
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=466257

Another resource "Making Shotgun Barrels" by Harold Hoffman
https://archive.org/details/Making_Shotgun_Barrels_By_Harold_Hoffman_Action_Book_Publishers/page/n1

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The conical-parallel is more common than plain conical chokes.

One simply makes a tube, then mills or grinds away anything that doesn't look like a choke.

There are swaged chokes too. The barrel is driven into die.


"The price of good shotgunnery is constant practice" - Fred Kimble
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Possibly of interest
“Experiments With (the length) Of A Choke Bore”
Forest & Stream, January 28, 1905 originally published by The Field (London)
https://books.google.com/books?id=6JbaHddByIUC&pg=PA84
A choke constriction of .016” and choke length of 3/4”, 1/2”, 1/4” and 1/8” produced essentially the same pattern percentage.

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Lefever claimed in a 1909 Forest & Stream ad to have originated "the taper system of choke boring".
This is the description in Hunter-Trader-Trapper August 1912
Click here, then on p. 73 for the entire article
http://books.google.com/books?id=Uy...=onepage&q=Lefever%20gun&f=false

[Linked Image from photos.smugmug.com]

An occasional Lefever 12 gauge has bores tapering from the breech to the muzzle (.756 to .708 and .715 courtesy of Daryl Hallquist), some have a parallel bore and choke taper of 4 inches, and others a standard 2 – 2 1/2 inch taper.

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Somewhere in the past issues of Gun Digest there is an article titled "Heat it and Beat It" about forming crude choke by simply swaging the lip of the barrel with a conical swage and a hammer. Understandably this was a single barrel with no rib. Despite the crudeness the results on the board were comparable to more sophisticated choke types.

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Drew, magic occurs when a shooter stumbles across a gun with stock dimensions that fit him physically, handling that suits his physiology and psychology, aesthetics sufficient for pride of ownership ("---my gun is more beautis than youon" or my gun is uglyer than yourin"; whichever), fit for the shooter's main purpose, etc.

I'll opine that the Orre will deliver an improved mod pattern; not more or less. Until Dr. Jones published his book there simply was no way to really test patterns. We all did it on an experience judgement basis, but not hard, defensible, statistically valid numbers.

DDA

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Shotgun wisdom for the ages smile
Don Amos AKA “Rocketman”
Shoot what fits you, what you shoot well, and what you enjoy shooting. If you find a gun that fits all three of these…never, but never, sell it!

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Drew and others, I have had two guns with the chokes tapered from the breech to the muzzle as Lefever described. Both were Lefever crossbolt [not sideplate] guns. One was a 5B the other an Optimus.

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Daryl, do they pattern as the choke is marked/measure or do they pattern more open? In theory, the longer the taper the more choke effect is lost.

DDA

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Yes, Daryl, how do the full taper guns pattern, especially with the best of modern wads and hard shot?

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I would love to know as well, Daryl.


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Sounds like a load of "hooey" BUT- My A.J. Aubrey 12 bore 30" Damascus barrels give amazing patterns with RST 2&1/2" No 8 paper loads, and not just on paper either- I love smacking incoming "Arch-angel" barn pigeons, and this Aubrey, grade unknown to me, has both barrels that pattern as tightly with my L.C. Smith Ideal "LONGRANGE" , shooting the same exact shells- One thing I can't figure out re: the A.J. Aubrey gun, there is no visible expansion joint on the top rib, near the receiver end- RWTF


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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 12:59 PM.
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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.


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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


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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

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Thank you, Don. Understandable for even a non-engineer, such as myself.

SRH


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http://www.claytargettesting.com/study2/Study2.2.pdf
Full choke is 25-50 fps faster than cylinder at 4 feet

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Doesn't some gas always exit the muzzle before any shot or shot container? I have always wondered if such gas would tend to hold the petals of shot cups closer to the pellets regardless of choke.

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That's a good question, Hal. I know that seals in hydraulic cylinders that are shaped with a lip, similar to the bottom of some shotcup's rims can contain thousands of psi in liquid. I have kinda always assumed that they do a far superior job of sealing off the gases than the old card/fiber wads did. But, do they completely contain it, 100 percent? IDK.


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There was a Gun Digest article by a Danish engineer in the early 90s, on how choke works. It was awarded the editor's prize if I remember right. It stated that shot is affected by choke in a similar manner that water is affected by a constriction on a hose, making the central core of the shot fly out faster. This is an oversimplification from memory, the article had lots of diagrams showing the choke effects on shot and very long text analysis.

The "squeeze" theory seems to be supported by high speed photos of ammunition makers showing shot from choked barrels exiting the muzzle in a long string, contrasting sharply with the short fat columns exiting cylinder bores.

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Ed Lowry, American Rifleman, "The Effect of Shot String", November 1979

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[Linked Image from photos.smugmug.com]

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Would be interesting to pick up some used shot cups and check for 'leaks'. Should also show up on high speed photos.

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