I have a Grizzly tube fed w 12" barrel, and when I got it the choke tube wasn't threaded in all the way, the previous owner was concerned about it so he didn't crank it in. I took it out, cleaned male and female threads the best I could, and lubed it up with antiseize grease, and cranked it in. It was a leap of faith, and it took a lot of sweat, but it did seat flush with the barrel. I believe it was a Mossberg choke. My point is, I had to really lean on it to get it in the last bit, but it went.
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