Posted: Thu Sep 19, 2013 8:58 am

Does anyone know the exact gunsmith process of fitting a barrel to an older model 37?

See below

Is it just a head space thing, or is there serious barrel smiting involved?

See below, needs machined on a lathe

Is it possible to have a barrel that is fitted to another gun fit on yours with no problem?

About the same odds as hitting the lottery

Can I just head space a barrel myself and if it checks out, is it okay to use or is there something I'm missing something?

Missing something

My local gun guy might know someone with an ICYL barrel for my pump and I wanna jump on it if possible and I am wondering exactly what my shotgun will have to go through to get it working properly.

Keep in mind that it will cost at least 100.00 to have a barrel fitted. That translates into shipping both ways, 75.00 that Les says he charges, I do not know the local rate here by me.

He says that pre-855,000 guns are interchangeable with other pre-855,000 guns based on how old your barrel and shotgun are, but I have heard this is false from a variety of forum members and old timers at the gun club. Is there any truth in what he says or has he been miss-informed?

He is smoking crack. Just kidding, he had it turned around.
The newer POST 855,000 barrels are interchangeable.
The older barrel threads (pre-855,000) had a pitch to the threads, just like on a bolt. There is a dimensional relationship between the barrel face, the shoulder at the end of the threads, the face of the receiver and an internal shoulder.
This is why the barrels are serial nbr'ed to the receiver. There will be a serial nbr on the front face of the receiver, running vertically next to where the barrel goes in, and the serial nbr on the barrel that also has a - (dash nbr) to indicate choke. Such as 543123-2 indicates a MOD choked barrel.
Ithaca choke marking system: '1' for Improved Cylinder; '2' for Modified; '3' for Improved Modified and '4' for Full choke. There were also Skt marked barrels (or maybe nbr 5)
In order to fit the barrels (from what I can tell by observation and talking to other folks) the barrels were screwed into the receivers and a 'witness mark' put on them. If you look at the older barrels most if not all will have the witness mark. All of mine do (older ones). The witness mark allowed them to align the barrel in fixtures to cut the thread interrupts, the extractor cuts and to put the barrel lug on.
Most pre- barrels will not even start. You can fudge them by backing them out a little but then they won't headspace correctly. If they do start, they will usually stop before going into position.
Because the threads have a 'pitch' to them, the barrel is actually pulled into the receiver a small amount, just like a bolt is pulled into a nut/threaded hole when turned. A 1/4 turn does not translate into much movement, but it is there and has to be taken into account.
To fit a barrel, the barrel face and the shoulder have to be carefully machined on a lathe a little at a time until the barrel will go into the receiver, start into the threads and then when turned, bottom out with the all the aforementioned features in alignment. A person has to understand the dimensional relationship before hacking away at the metal.
As I posted, there are 2 gunsmiths that I know of that I would trust to fit the barrels. Other good gunsmiths if they take the time to understand the dimension relationships could do them also, but they have to take the time to look at the design.
The post 855,000 barrels simply use parallel V grooves, which allows barrels to be swapped back and forth. Sometimes due to pre-CNC machining practices/tolerances, even those might need a little adjustment.