Good news, I finally figured out what the problem was and my rifle now fires every time the trigger is pulled. I took lots of pictures and I'll go over what I did to make it work properly. The work I did last week on the locking bolt did not cure the fail to fire problem, but I believe it still needed to be done. Today I took my Rio Grande and my 336 from the safe so I could compare the two side by side and try to figure out once and for all why my RG wouldn't fire every time I pulled the trigger. The first thing I discovered was that the hammer on the 336 would travel forward until the hammer would strike the rear of the breech bolt. The hammer on my RG was stopping short of this position. The first picture shows the gap between the hammer and the rear of the breech bolt, and the second picture shows the hammer on my 336 and how it's fully against the bolt.
The next picture is a side by side comparison of both breech bolts, they are so close in size that they will fit in either gun.
I was concerned that something might be interfering with the firing pin keeping it from properly striking the primer. On the left is the 336 and the RG is on the right. As you can see there was nothing keeping the firing pin from protruding from the bolt face. The RG firing pin was actually longer than the Marlin.
The next two pictures were taken after pulling the trigger, then recocking the hammer. The first is the RG and you can see how the rear firing pin is still sticking out the back of the bolt. The second picture shows how the firing pin on the Marlin is driven all the forward until the back edge of the firing pin is flush with the back of the bolt.
The next picture was taken with the breech bolts removed from both rifles and the trigger pulled. You can see that the Marlin's hammer is able to fall further than the hammer on the RG. It's evident that something is preventing the hammer on the RG from fully striking the firing pin.
Just so you know what I'm talking about, this is the tube of Prussian blue that I used to find what was stopping the hammer short from fully striking the firing pin.
This is the area of the receiver that I coated with the Prussian blue.
After coating the inside of the receiver with the Prussian blue, I pulled the trigger. I removed the hammer from the gun and you can see in this picture where the hammer was making contact with the receiver. The Prussian blue was transferred from the receiver to the hammer wherever contact was made.
Another picture of the hammer, it's easy to see that it was making contact in the area of the cross bolt safety.
I brushed some %@*&$ Red on the hammer to make it easy to see exactly how much metal I was removing from the hammer. Then I clamped the hammer in a machinist vise to act as a guide and to keep me from removing too much metal. This is what it looked like when I first started to file the hammer.
This is what it looked like when I was done removing metal from the hammer.
This picture is a little fuzzy, but you can see that the hammer is now free to move forward enough to make contact with the breech bolt. This now lets the hammer drive the firing pin into the primer, firing the gun.
When I was finished working on my gun and after I had put both rifles back together, It was too late in the day to go to the range to test fire my Rossi. While I was at the range last Wednesday, the RG failed to fire on the first strike at least 80% of the time. What I was able to do is, I grabbed six cases that had been sized and primed, but I hadn't loaded the cartridges yet. I went out in the garage and closed all the doors and windows. Then I grabbed a cardboard box and taped it closed except for a slit to stick the muzzle through. This kept the noise from the primers being fired, down to a level that no one called the police. All six primers were ignited on the first pull of the trigger. This gun hasn't fired more than twice in a row before having a misfire, so six in a row is one heck of an accomplishment. I might actually now have a gun that I'm not afraid to take hunting.