Buggered choke threads


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Oldnamvet
December 20, 2007, 07:57 PM
A friend of mine called and had a problem with the screw-in chokes on his shotgun (don't know the brand). Evidently, he inadvertently put in a choke tube from another non-compatible manufacturer. It went in kind of hard and when he took it out the threads were screwed up. Now, when he puts in the correct tube (goes in hard as well), the threads come out screwed/chewed up. Is there some kind of thread chaser that he or a gunsmith can run down the barrel to straighten things out or has he pretty much totalled the shotgun, requiring surgery and re-threading?

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BEARMAN
December 20, 2007, 09:02 PM
Take it to a gunsmith that installs that type of choke, he may be able to chase the threads and it may work. Or he can shorten the barrel and rethread it. But tell your friend to stop changing the choke until this is straightened out , he is not helping the situation by changing the chokeswith damaged threads.

Pete409
December 20, 2007, 11:49 PM
I agree that the gun should be taken to a gunsmith who MAY be able to chase the threads and cure the problem...... or maybe not cure the problem.

I don't agree that it's possible (in most cases) to simply cut off the barrel and rethread for choke tubes. If you look closely at most barrels which are threaded for choke tubes, they are larger in diameter out near the muzzle. This is so that there is enough wall thickness to thread for and accept the choke tubes.

When you cut off 3" (or whatever) of the end of the barrel, you probably won't have enough wall thickness left to install a threaded choke tube.

BEARMAN
December 21, 2007, 12:57 AM
We have no idea what make of gun this is, taking it to the gunsmith MAY fix the problem, he MAY come up with another option,or it MAY need a new barrel if screw in chokes are required. It is all speculation for us but a knowledgeable gunsmith should have the answer.

kirbythegunsmith
December 21, 2007, 02:49 AM
When threads are damaged at the entry section, the chances of starting a cutter at the proper position are a roll of the dice.
Special tooling, dressing away the most damaged section, or other salvage operations short of a hacksaw can improve the chances of a satisfactory re-cut.

Even if a cut is started mis-timed/mis-located vs. the original, once the threads have been chased to full depth (can't go half-way here), as long as the parent metal has not had a large portion removed by this secondary cut, the retention will suffice.
Your tube may exhibit a larger amount of play in the threads.

In my shop, I would want to measure the remainder material after any thread repair to calculate the change in the thread minor diameter of the hole vs. the major diameter of the tube threads. That comparison can ensure that the contact is sufficient for the situation.

This job can also be buggered by someone not careful and familiar with the principles of choke alignment. A factory hole is likely to already be threaded off-line, and any re-cut should not add more error to the equation.

In other words, if you start a tap crooked into an existing hole, not only will you remove excess metal in the thread section of the hole, but any excess angle can start the tap on an offset line that forces it to continue ever deeper on the side of interference. The re-cut on the opposite side diminishes with the increase of cut depth.

Part 2: When cutting off a barrel that has an enlarged muzzle section for the choke threads, the reduction in outside diameter may prohibit the re-install of the original thread, but an alternative choke may possibly fit.

I have installed my custom chokes in barrels that other shops have declared too thin to have choke tubes installed. I also make every choke tube to be a precise fit and of the choking action that the shooter prefers. Sizing mass production tubes every .005" may be convenient for production, but barrel size is too subtle for me to want to use such coarse dimension jump.

kirbythegunsmith@hotmail.com

Flyrodder
December 22, 2007, 12:47 AM
Kirby: I have a Remington 1187 20 ga. that patterns low and left from point of aim. It shoots to the same point of aim with both chokes I have. The top right edge of the pattern hits the point of aim. Can the pattern be centered without the barrel being noticably bent or will it have to be cut off and rethreaded or have a Poly choke installed? Thanks, Flyrodder

kirbythegunsmith
December 22, 2007, 01:33 AM
Those that have been reading my posts know that I am not happy with the lack of accurate alignment of choke installations, since my first rude example was hitting about a foot off at 20 yards.
When I verified that with the shooter that had just bought that new primo screw-in choke barrel for his classic, and also saw a $7000 trap O/U with tubes installed crooked by the factory (about 17 years ago, and I think that much money could have gotten you a new Malibu), I knew better than to automatically expect decent alignment in ANY barrel.

A shotgun barrel with a mis-aligned, crooked threaded hole should not be expected to throw the best pattern, even if you could bend the barrel to make it hit closer to where you point.

The shot still has to change direction when being choked at the same time, and the force of re-direction is bound to increase the pellet deformity on that side of the shot column. No quibble will affect the physics of that situation, with the only point of conjecture being of the level of the perceived problem. Some might say "inconsequential" or similar, but don't say that there is "zero" effect.

Specific answers about a barrel may not be guaranteed, but I do expect that when I am deliberately putting the choke hole in straight, that you will have a better chance of satisfaction than when someone else deliberately doesn't seem to care about accuracy.
I can't say that the barrel will shoot perfectly straight, even though the hole is straight.
Remember, I didn't put on the rib or put the curvature into the barrel, if present.
The best test is for the barrel to be cut and crowned, then test-fired for point of impact verification, if that's worth the extra money for verification prior to the installation of the choke threads.

Let me know if you need more particular details.

See my previous postings for more insight from a gunsmith.

kirbythegunsmith@hotmail.com

Clark
December 23, 2007, 11:48 AM
My brother bought a nearly new Rem 870 with misaligned choke threads.
The shotgun patterned way off, and you could see that the threads were at an angle.

I offered to cut off the choke, boring bar, special reamer, and Rem Choke tap the barrel for him, but he worried it would destroy the resale value.

Maybe he was just afraid of my workmanship:)

I have done allot of Rem-chokes, and I have come to the conclusion that they take too long to do, with just the reamer. I try to take out as much material as possible with a boring bar to speed it up.

Also, the tap is too hard to turn, I use the big lath and power tap.

langenc
December 23, 2007, 09:19 PM
I gave my son an old Ithaca 37. He decided to get tubes put in it. The smith told him no-the hole is not in the center of the barrel. So he sent it to Ithaca when it was emp owned and got a new barrel w/tubes and a 3" chamber. Cant use 3" as the ejecting port is too small. I told him I get first right of recall if he ever decides to get rid of it.

kirbythegunsmith
December 25, 2007, 11:40 PM
Clark, I would be careful with your technique.
Power tapping is fraught with danger if the tap over-cuts the bottom of the hole. The seat is ruined and allows crud to pack under the end of the choke tube and can hydraulically lift the edge of the tube to cause a bore obstruction and blow out, in extreme cases.

The other condition that is even worse is cutting away enough of the seat to leave the edge of the tube exposed to direct impact of the shot column. The amount of material that must be mistakenly chamfered is very small when the bore size is close to the size of the interior diameter at the entry end of the tube.

http://i186.photobucket.com/albums/x109/kirbythegunsmith/tappedpast-6.jpg

That shows a small amount of chamfer into the seat edge and the tube edge is next to the bore with a minuscule error in depth.
Power tapping is a brute force method not easily subject to finesse.

A tap that is too hard to turn by hand is dull. A reamer that cuts too slowly is dull. The manufacturers sometimes have a hard time caring that their tools are made improperly: they can't hold an edge, have mis-spaced flutes, poor tolerance control, and more problems that I have personally found.

The worst example that I have was so over-cut that the tube had no seat to hit, per se, but would slowly be curled inward at the back end by being threaded into the chamfer so overcut that the seat was not there at all. Everytime the tube was tightened, it went in deeper than the last time, and the shooter had gone through extra tubes due to that condition.
There was an angel over that guy's shoulder, as he was so lucky not to have a rupture occur before I saw his barrels. What a way to treat a Browning BSS 20 ga.

Sunray
December 26, 2007, 02:47 AM
"...the threads come out..." On the choke, the barrel or both? Choke tubes are kind of thin, but a die of the correct size should fix the choke tube. A tap, again of the correct size will clean up the barrel. The downside is that taps and dies of those diameter aren't exactly cheap and may well be a special tap and die. Tell him to call a few shotgun smithies and get a quote. It may be cheaper to buy another barrel with chokes and cut of the damaged one, recrown and install a rifle sight.

Clark
December 27, 2007, 01:53 PM
1) I am set up for 12 ga Rem Choke in a few pilot sizes.
I can only modify half of my massive beater shotgun collection.
Many of the barrels are too thin for my 32 threads per inch system.
I need a barrel to be .845" diameter.

2) Winchoke is also 32 TPI and needs .845"

3) The Tru Choke system with 44 TPI needs at least a .825" barrel muzzle.

4) The Tru Choke Thinwall aslo with 44TPI needs at least .805"


And don't try to cheat on those dimension requirements.
You have to know what you are doing, the bore must be centered in the barrel, you need good equipment, etc.

When Randy Ketchum does it [he is a real gunsmith], he cuts off the last 2", only to find that the bore is off center sometimes. I use the whole length of the barrel and spend too much time reaming out the old choke steel mass, so I have gone to a boring bar to prep for the reamer.

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