Fixing A Colt Walker

Might be possible that the lug on the hammer is worn. I would remove bolt and if there is nothing obvious bad look at the hammer. The bolt should not drop untill the hammer is cocked.

This sounds like the hammer is being blown back upon being fired. This would withdraw the cylinder bolt enough to allow the cylinder to rotate slightly. If the hammer was not being blown back, it would prevent the rotation of the cylinder by being "trapped" in the nipple cut-outs. I would first check on the flash hole in the nipples and see if someone hadn't enlarged them significantly. That would cause what you describe. On a used revolver it is also a good idea to take it apart and see if the parts are worn or damaged. You may also have a fatigued or broken trigger/bolt spring. Removing the grip frame will expose these parts.

Don’t dry fire a cap and ball revolver, you’ll wind up mushrooming the nipples.

More than likely, your problem is a too shallow bolt engagement in the cyl locking notch. It's fine to reduce or remove the "bolt stop shelf" (the extension forward of the bolt head, the bolt head is what engages the cyl locking notch) which will allow the bolt head to "bottom out" in the locking notch. If you remove the bolt stop shelf, you may have to push the bolt down with your finger, when you have the cylinder off, so it will reset and be drawn down into the frame when you cycle it next. But, it will ensure " full engagement " of the bolt. Some Smith's/tuners do that (remove the bolt stop "shelf" ) on all S.A.s (that have them) as a normal procedure.

You should be able to see a mark on the bottom of the locking notch as evidence of bolt head contact.

Mike

whughett said:

Don’t dry fire a cap and ball revolver, you’ll wind up mushrooming the nipples.

Click to expand...

Quite true. I never do with mine.
Even after many years my nipples are still in perfect condition.
My revolver cones are fine too.

It might be worthwhile to examine the trigger and bolt spring to see if it is operating correctly. Perhaps it is weak or obstructed by debris.
Since your revolver is used it might even be a makeshift substitute part. Try removing the cylinder and pressing down hard on the bolt with your thumb. It should exert a heavy upward force.
Also, it occurs to me that this revolver uses oval shaped bolt stops and an oval shaped bolt. Is the bolt or the stops worn?
Is it possible that the bolt or the stops have become peened out of shape such that the bolt does not enter to full depth in the stops?
Can you rock the cylinder out of engagement with a stop by rotating the cylinder by hand when it is locked and the hammer is down?
Is there excess end play in the cylinder? If so, perhaps the hammer blow pushes the heavy Walker cylinder forward enough to cause the oval bolt stop to over-ride the bolt and unlock the cylinder.
Just some things to check.