Theoretical barrel swamping methods.

[mikeyfirelock]

I have wondered exactly how the old guys did it.   I’m sure they used a grinding wheel, and I’ve wondered if they figured out a way to set the barrel up in a fixture with unequal length arms at each end.   Moving the barrel back and forth against the grindstone should give a swamp wouldn’t it ?   Wouldn’t be perfectly straight , but with the correct length ( ie long enough arm) it would seem to be possible to come close to a straight flat, and use a shorter arm at the other end to get a more rapid taper .   Think parallelogram with one shorter end.
Or am I just tired of inletting a swamped barrel tonite ?
Mikeyfirelock

[Daryl]

Might some of it been done on the anvil, when forging?

[bob in the woods]

Might some of it been done on the anvil, when forging?

That is my guess as well.  The welding process is actually conducive to having some degree of "swamp"

[davec2]

Quite some time ago I read somewhere about barrels being swamped by flexing them upwards (at the desired point of the waist) in a set up on a mill table and then taking a straight pass with a fly cutter.  Four of the flats are done with the same set up and the remaining four are flexed over a block that adds the amount removed from the barrel at the waist on the first four.  When I first read about this, I thought it was a fairly drastic treatment of a barrel.  However, since then, I have had to straighten a few barrels and came to understand how far you actually have to flex a barrel in order for it to take even a very slight permanent set....far more than the barrel would need to be flexed to produce a swamp by this method.  Does anyone know more about this process and if there are more problems than I see with it ?

[Daryl]

This barrel needed to be stressed more, to take on a permanent bend, as when this "fixture" was removed, the barrel was straight.
It needed to bend a tich, to shoot to the sight.

[davec2]

Daryl,

That's exactly what I'm talking about.  To actually bend a barrel you would need way more flexing than it would take to straight mill an appropriate swamp.  Even without a milling machine, if the barrel were clamped with the appropriate amount of flex with a couple of straight guides on either side, it would help guide a file or grinder ....or whatever.  Perhaps more controllable than just doing it by "eyeball".

[Karl Kunkel]

Daryl,

That's what I also have heard, that the basic swamp was created during the forging process.

[Jim Kibler]

Daryl,

That's exactly what I'm talking about.  To actually bend a barrel you would need way more flexing than it would take to straight mill an appropriate swamp.  Even without a milling machine, if the barrel were clamped with the appropriate amount of flex with a couple of straight guides on either side, it would help guide a file or grinder ....or whatever.  Perhaps more controllable than just doing it by "eyeball".

Yes, but the bend isn't symmetrical about the length.  Typically there is a substantial flare that starts a relatively short distance from the muzzle.  Bending to produce this may exceed the elastic limit.

Jim

[RAT]

I'm in the camp that says the flare at each end is (mostly) an incidental byproduct of the forging process. When you "stretch" a piece to make it longer, you're naturally going to hammer it in the middle and work it towards the ends. Yes... having it thicker at the breech end makes that part stronger... and yes... having the muzzle larger can help the balance... but I believe that was more a happy coincidence than the object of the exercise.

[rich pierce]

Having the muzzle flare eliminates the need for a front sight with a very high blade.
Reasons for swamped form:
Thickness at breech without excess weight
Balance and weight savings
Sights at right height almost automatically

[Jim Kibler]

Look at Jaeger barrels.  No way that is an accident or just a consequence of a forging technique.  Not reasonable.

[Longknife]

Somewhere there is an illustration of a period barrel grinding machine. It depicts the shop of a barrel maker, and a worker is seen grinding a barrel on a tabletop grinding stone. I can't remember what book it is in. Anyway, in the early 1980's I began making a barrel "swamping" machine that consisted or a long table with a grinder wheel mounted underneath with the wheel protruding up through a slot in the table. It was powered by an Elec motor. My plan was to have the wheel/motor adjustable up and down. Next there were two sets of tracks (angle iron) meeting at the center of the wheel that were adjustable up and down at the wheel. The barrel then was mounted on centers in a carrier with a grooved wheel on each corner and it rolled back and forth on the tracks and would grind a swamp in the barrel...I think? I never got the barrel swamping machine completed but I still have the barrel carrier with mounted wheels in the corner of my shop.,,,LK 

[Karl Kunkel]

I think the basic swamp was established during the initial forging, but I don't think it was a happy accident.  I believe it was intentional.  The knew what they were doing.

[GrizG]

If I may... I worked as an "old timer" at Williamsburg and assisted Jon Laubach in forging swamped barrels. His son Chris is the lock maker who participates on this site (or did??)...

The barrels were intentionally forged to have taper. A very basic description of this is the taper was started by creating a "flat" iron skelp that tapered in thickness and width. The skelp was then heated and rounded into a trough by forging on a swag block. Next the edges are wrapped, starting in the middle of the length, and forge welded lengthwise around a mandrel*. It takes many heats in the forge and lots of hammering to do this! The resulting barrel is thus by design thicker at the breech and tapers towards the muzzle. 

The flared muzzle is created by "jumping" the barrel. Jumping involves heating the barrel and driving it into the face of the anvil to expand and thicken the barrel near the muzzle. This step too requires multiple heats and you have to maintain a hole through the barrel. If you close up the hole through carelessness you cannot get a reamer through it... barrel drilling wasn't possible in the 18th century so you may have scrap with which to make a new skelp.   

The barrel taper is made more uniform and straighter through heats and hammering and then the flats are forged... again using a mandrel near the ends to preserve the hole. Later the flats are filed...

*The mandrel is a steel tapered rod that is used to maintain a hole for future reaming... it will not get welded into the barrel as it is never brought to welding temperature... it only gains heat from being inserted into the hot skelp during welding.

There are a LOT more fine details involved in the forging, dimensioning and quality control but this description gives you a good idea how it was done. A good eyecrometer is crucial throughout the process as are some gauges... 

Note that there is a barrel forging video featuring Jon and Chris floating around. It's title "Forging a flintlock rifle barrel with Jon Laubach." I do not recall who produced and distributed it...