SECURITY SIX OPENING HARD

I bought a used Security Six that operated fine until recently. The thumbpiece will not push the center pin to open the cylinder. I can rap the thumb piece gently with a rubber hammer and it will open the cylinder. With the cylinder open I can use the flat of a screw drive against the center pin and it moves freely. I replaced the thumb piece same thing.
I think i might have a burr on the hole in backing plate . Any ideas ??

First, loosen the cylinder release pivot screw a 1/4 - 1/2 turn or so and see what happens. There are times that the pivot screw tightens up and causes binding or gets bent just a small amount.

Then, open the cylinder and use a small punch or screwdriver to press in on the cylinder release depressor cone to see if it binds when pushing it in. When you release it, it should come back out on it's own to be flush with the recoil shield. If it doesn't or it binds going in, remove the release, the cylinder assembly and the trigger group assembly so you can look closely at that part of the frame to see what might be causing the binding. If you need to remove any burrs that might be there be careful that you don't enlarge the hole in the frame, that could allow debris into the inner workings and that isn't good.

I purchased a new cylinder release button and screw from Gun Parts and installed them, no change. I took it to a local shop and let them figure it out. I am stumped. Can not put enough pressure on thumb piece to open cylinder. When you get cylinder swung out you can push the center pin with a little effort. I removed the locking lug from the front of the underlug, it moved easily not hung up.
Thanks for the input

When you find out what was causing this situation, please let us know no matter what caused it.

Got my Security six back. The gunsmith said he found a burr in the center pin hole where the thumb pieces push the center pin forward to release the cylinder for opening. I tried it and worked smoothly. I am surprised with the quality of steel Ruger uses this would happen. He also told me he smoothed the tip of the thumb release where it goes through the frame.

Thank you for the reply.

I will not second guess your 'smith's findings.

But, after working on many Security/Speed/Service Sixes...Initially, without a hands-on examination, I've found that whenever the extractor length has grown, either from debris under the star, even just one kernel of powder, or the extractor/ejector has unscrewed itself even just a tiny bit, these same symptoms will surface.

I would still expect that was the culprit, and if a burr was in fact discovered, that may or may not have had any impact, but the extractor length was inadvertantly corrected during the teardown.

Wayno, yes that is exactly my experience with the six series. Many times.