It's something that I've been meaning to get around to, finally found the motivation and a little bit of time to do thread job on one of my Hi Standard Sentinels. barrel is internally threaded 3/8-40 with a custom male-male adapter that's 1/2-28 on the other side. The results? Not far from what I expected. The sound pressure is reduced, but quite a lot escapes the cylinder gap, and that didn't change by a significant amount using shim stock to keep the gap tighter during firing. It metered between 137-141 dBA with all .22 ammo other than CCI Quiets, which hovered around 129. Subsonic, standard velocity, high velocity - all in that range. It also made no difference using the full sized 5.5" Ocelot or 3.0" Ocelot Micro. On a semi-auto pistol, those cans meter on average 119 and 128 respectively with with subsonic ammunition. Conclusion? You can knock it down, but what comes out the cylinder gap is just barely hearing safe with .22s, and I'm certain would ring your ears good with anything bigger. While I don't consider this one to have been a waste of time, I'm not going to be threading any of the .32s, .38's or .44s with swing out cylinders. I do, however, still have plans to gas seal one of the Iver Johnson or H&R top breaks I picked up for that reason, which I'll post all about when I get around to it!