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Polychokes have been installed in a variety of manners, including the soldered and threaded situation, in that some have actually combined the threads with some flowing of soft solder to lock the joint more securely than tight threading.
I have seen wrenches to tighten the rear section of the body to the barrel, and it looks like a split-length handle with 3 different threads in the 3 central holes. That's one for each gauge, and when I first saw the device, it looked similar to an old split-die threading handle. The split allows the holes to be compressed onto the threaded portion of the collar to facilitate a tight grip. There are several screws crosswise between the threaded holes that are tightened for the clamping force application.
It could be that I also saw a smooth version that would clamp on the body section to the rear of the collar threads, but that version would possibly leave scrape marks if the turning force exceeded the clamping pressure, and that's not conducive to good customer relations. It may have been a rework of the threaded version, or a shop-made device.
The problem may be that some versions of the soldered collar type had not been soft soldered, but may have been silver brazed (soldered) which requires heating the metal to at least a low red glow.
I have seen versions that were induction brazed to the barrel. That technique is very precise in heat application location and amount. If that was with conventional "brazing" figure 1600 degrees F.+ to make anything move.
(If you were wanting to remove the choke so that you could sell it, the bodies are undersize inside, when new, so that they may be matched to the bore of the barrel. Anyone buying a used poly takes a chance in that the bore may not even be close to the size already cut, and I have seen plenty that were installed off-center, angled, bored crooked, and more sloppiness. I would never consider using the inner collar of a used poly.)
Conclusion: if you get to that situation, get a hacksaw. If you have threads on the end of the muzzle, get a hacksaw after you remove the choke. If it is turned just a small amount (since M-12 barrels are mostly small diameter) you may be able to blend with the rest of the barrel, but prognosis looks poor.
Yes, I do have both the threaded and solder-type poly's, external collars of both varieties, the Poly-Matic, Adjustomatic, Cyclone, and more, with most still new, and still in the plastic.
See my previous posts for more info.
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