My 648 Saga

[glenncal1]

So I am a big fan of .22 WMR (if you aren't no need to let us know) and own 48' in all three barrel lengths. Decided to pick up a 648 as Bud's had them at a good price and S&W was giving a $75 rebate.

Got the gun and it looked great, took it too the range and the first was right in the red bull, after the first couple cylinders in SA I started to get some FTF's. Ran a cylinder DA and had a ~50% FTF result. Did all the normal stuff, checked strain screw, different brands of ammo etc. No joy, sent to gun back to S&W.

They returned it with a list of stuff they had done and it was better but still way to many FTF's especially DA. The cases were being dimpled but the hammer strike didn't seem strong enough to ignite all the rounds. Took a strain screw out of a square but gun to see if more pressure would fix the issue. I had also read somewhere that sometimes the hammer block would interfere so I left the hammer out for the range trip.

Well the hammer block was the culprit. My shots with the extended strain screw (not screwed all the way in) were 100% SA and DA. I put the round butt screw in and it was 100% as well. Fired about 100 rounds: CCI, Federal and Fiocci 100% ignition.

Now my decision is whether to mess with the hammer block or just leave it out.

 

[Mercury]

That was a nice diagnosis you made there.
I would first look for and remove any burrs on the hammer block or its channel.
If that doesn't do it, I would suggest marking up the hammer block with Dykem or a colored magic marker and put it back in the gun to see what areas are interfering with the hammer. You could then stone or lightly file them so that it no longer interferes.
I would suspect that the area of interference is likely at the very top of the hammer block. It probably won't take much to dress it so that it functions correctly.

ETA: An additional suggestion