No machinist here but I would imagine that the choke install would have to be absolutely parallel to the long axis of the bore (up and down and left and right) and centered as well.

This assumes the parallel part of the fixed choke is parallel to and centered with the bore axis too.

jk

 

No machinist here but I would imagine that the choke install would have to be absolutely parallel to the long axis of the bore (up and down and left and right) and centered as well.

This assumes the parallel part of the fixed choke is parallel to and centered with the bore axis too.
jk

I would not disagree with you from a theoretical perspective if all barrels were perfectly straight and concentric. However, how do US gunsmiths maintain the required convergence in practice?

I've seen barrels being made in the Perazzi factory thanks to Mauro and his late father. The boring process was surprisingly simple. Note that I said "simple" and not "crude". While high attention to detail is paid in the barrel boring process by reputable gun makers, one has to wonder whether all shotgun barrels are to a similar standard when it comes to straightness and concentricity.

In the presence of such less than perfect bores, I come back to my question as to how US gunsmiths ensure the convergence of patterns in O/U guns they thin-wall is not adversely affected?

 

Choke installers can move the poi or leave it where it is.
It you require higher or lower they bore the threads at a slight angle.
If it turns out badly there is not much left to do other than making eccentric tubes.
Henry

 

Choke installers can move the poi or leave it where it is.
It you require higher or lower they bore the threads at a slight angle.
If it turns out badly there is not much left to do other than making eccentric tubes.
Henry

So Henry, are you saying that US thin-wall choke installers/manufacturers regulate the convergence of all the barrels they thin-wall using custom-made chokes specific and unique to every gun they thin-wall before returning a gun to a client?

 

Bushings. Which of course requires the barrels to be properly regulated, unless as Henry said the desire is to change the POI, then likely different bushings, and lots of experience

 

Drew,

Many thanks. That's a most interesting video.

A couple of points:

1. I was surprised that the workpiece (the gun muzzle) was held in the machinist's hand during the reaming process. Is this the way holes are bored/reamed by NASA in the world of precision instrumentation? Surely not? Remember I'm an electrical engineer and a physicist not a mechanical type so I don't know.

Machining Hole-making Process, Opertaions, Tools, Machines

2. The process shown in the video explained how the portion of the barrel is modified to accept a choke tube. It didn't deal at all with where the barrel shot before or after having had a choke tube fitted. I'd consider it a leap of faith to assume that the barrel would print in exactly the same place as before the modification without checking and if it didn't, what remedial action would the gunsmith take if any?

Jim

 

I'm sure they have a pilot on the end of the reamer and tap to keep things aligned.

 

1. I was surprised that the workpiece (the gun muzzle) was held in the machinist's hand during the reaming process. Is this the way holes are bored/reamed by NASA in the world of precision instrumentation? Surely not?

if that makes you nervous watching Herb Orr work on a barrel would have given you heart palpitations!

 

I already have atrial fibrillation so I'll pass thanks.

 

Great question.

When some well-meaning shooters told me to get my 682 X Trap Gold choked in this manner, I asked a gunsmith and engineer acquaintance to do it. He refused, citing this exact concern, and saying it would probably be right but as he couldn't guarantee it, he would not do it.

I then asked another provider who casually said "Sure, it'll be fine, send it over" without explaining HOW concentricity would be guaranteed.

I then got in contact with Neil Winston who threatened me with all sorts of dire consequences if I messed with it.

So I didn't.

 

This is a funny discussion. I am a toolmaker by trade, and to the average joe, I could see why this would worry you.

Any respectable gunsmith/machinist/toolmaker should have zero issues installing thin walled chokes into a gun perfectly concentric with the existing bore whether he does so by hand with piloted tools or in a machine tool such as a lathe or in a fixture designed to maintain concentricity.

 

I would refer you to my first and subsequent posts. My interest is not in the maintenance of concentricity, it is about maintenance of "convergence" of the pattern from both barrels at the distance targets are shot when using O/U shotguns in which thin-wall chokes are fitted.

 

If I was to perform this operation on a set of barrels I would first fully inspect the concentricity of the existing chokes to the existing bores. I would then record any error or lack thereof and duplicate it precisely in the machining process for the thin wall chokes, thus maintaining the pre choke tube convergence point.

As an added measure of assurance, I may even pattern the gun prior to machining and then pattern with the choke tubes after machining, just as a practical check to the quality of my work

Concentricity (or lack thereof) and convergence point go hand in hand

 

Have you ever fitted thin-wall chokes?

 

I have not

 

Choke installers can move the poi or leave it where it is.
It you require higher or lower they bore the threads at a slight angle.
If it turns out badly there is not much left to do other than making eccentric tubes.
Henry

If Briley can offer custom chokes to adjust POI, (Which they do) I would think adjusting POI while installing chokes (They are the leading thin-wall choke maker to boot) would be easy for them. Yes, there is less barrel material to work with installing thin-walls, and thus less divergence from concentricity available from the barrel walls, but combining the use of the two methods of altering POI (and thus convergenge) one should be able to put that load of shot anywhere desired at any distance within reason.

 

Briley expects you to accurately test your own poi and tell them exactly what you want.
They only need the barrel or barrels because they typically do not do pattern testing.
The work they performed for me turned out good. It's not guaranteed that your barrel work will turn out good. However odds are in your favor.
Henry

 

I'm going to gracefully bow out of this discussion. I do not have empirical data to present. I am only relying on 12 years of trade experience in the heavy artillery manufacturing field and a total of 18 years experience in toolmaking that includes the manufacture of much more complex and precise devices than shotgun barrels

 

Hmmmm.

"An appeal to authority is a fallacy in which a speaker seeks to persuade not by evidence but by appealing to audience's perceptions of his expertise."

 

the reamer and tap to keep things aligned.

 

I would not send a "perfect" barrel out for work, Buy another set with chokes. I would hate to end up arguing with a gunsmith over a set of barrels that could not be replaced because they were "perfect" to start with,

 

I would then record any error or lack thereof and duplicate it precisely in the machining process for the thin wall chokes, thus maintaining the pre choke tube convergence point.