doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Choke dimensions and type?

I recently bought an English hammer gun made in the late 1870s. Measuring the choke showed a strange pattern-at least to me. The bores constricted by 10 pts in the left barrel about 4" from the muzzle and then opened back up to cylinder bore in the last 2". Same in the right but only 4 pts. The barrels are marked "choke bored". It is a Birmingham gun of good quality. A GE Lewis with the London address instead of the Birmingham address.
It seems to me Gough Thomas wrote about this type of choke but I can't remember . Can anyone give me some information about what to expect as to probable pattern? I'm going to shoot 7/8oz 2" shells in the old gun.

I would say the barrels are jug choked. Often this occurs where barrels have been lapped out to remove pitting or some other defect and a proficient barrel worker will adjust to allow for some choke (and reasonable remaining wall thickness).
Patterns should be the same as any gun choked approx 1/4 and imp cylinder. I have had several hammer guns choked in this way and all threw acceptable patterns.

If I am understanding the dimensions correctly, this is the reverse of a jug choke. On a jug choke the bore would enlarge, then choke to cylinder dia at the muzzle, thus the "Jug". This one is stated to constrict down then enlarge back to cyl. Sort of hard to "Jug" in a reduced area.

I'd bet on the barrels being honed at some point to remove pits.

Agree with Miller that it sounds like a strange version of jug choking. However, it does seem to fit the description for barrels marked CHOKE rather than NOT FOR BALL under the proof rules of 1868:

" ... barrels, the bore of which was enlarged immediately behind the muzzle, but except for such enlargement, and also except for the chamber or recess containing the cartridge, the bore was not in any part of it larger than at the muzzle."

I didn't think Miller said that.

If the barrels were homed it is in a strange pattern. In 130 years most anything is possible.
Yep it is the reverse of a jug choke. I went back to GT Garwood last night and couldn't find the bit on choke but I only found one of his books.
I'm going to give it a try this weekend and I'll see what it will do. If it blows up -well I hope I keep my fingers.

Remington used such a choke in their 1100 and 870 skeet barrels in 12 and 20 gauge. I don't recall about the 28 ga. barrels. However, they use a standard type choke in the 3200 skeet guns made during the same period.

In the field of gas dynamic, this would be refered to as a convergent/divergent nozzle - commonly used as a rocket motor. The convergtent section is designed to accelerate the gas to its sonic veocity followed by additional acceleration in the divergent section; note that the convergent section can't accelerate the fluid to above sonic velocity. Who knows what the sonic velocity of a shot swarm is when it is acting as a semi-fluid - - - not me!!!

I'd expect these chokes to act enough like any choke of equal constriction as to be indestinguishable. Winchester WS-1 skeet #1 is of the convergent/divergent design. I've not been able to find any benefit or liability in patterns from this design.

DDA

Pretty interesting that should be found in so antique a bbl. but ya gotta know that the inquiring minds were prolly trying every possible permutation of choking imaginable in those years.

And most of a century later the above became most of a Tula choke, which just took the idea one small step for mankind further. And by all reports performed in a wonderfully positive way.

Once again, just goes to show - The only thing new is the history you don't know - a tip o' the hat to Will Rogers

have a day

Dr.WtS