I had Mike Orlen machine and tap a single barrel (870) for a Colonial Arms Thin Wall choke tube. I went to put one in the other day (for a feral pigeon shoot) and the choke tube was considerably smaller than I think it should be. It wobbled when I was putting it in. It snugged up when it got all the way in but I'm sure it wasn't right. I haven't been able to reach Mike on the phone yet but I'll keep trying.
If I can't reach him: Any idea on what other choke tubes I should try? Not sure if Mike checks in here any longer.
