Problem with my oldest Contender

[Bullseye]

My oldest Contender has a problem.

First of all I have had all these barrels for years and all have been shot on all my frames.  All the rounds are loaded with the same brand of primers and always have been.

Problem is when I put my 45/70 barrel on my oldest frame I get a mis-fire with a very light indent in the primer.  I put these same rounds in my 45-70 Marlin and they fire.  This barrel has been shot many times on this frame.  I then put a 375 Win and 223 barrel on this same frame and they all fire with a nice correct looking indent in the primer.

I then put the 45-70 barrel on a different frame and it fires fine with a correct looking indent in the primer.

I would assume the problem could be that the locking bolts are causing some kind of problem on the one frame even though this does not make sense since the barrel has been shot before on that frame.  I assumed the problem was with the firing pin or spring when it first happened but since it is only with one barrel I am confused.

Any ideas before I take the frame apart?

[Slowpoke Slim]

That frame could just need a really good cleaning. Maybe some grit or powder residue has built up inside the frame not allowing the barrel lugs to fully protrude into the frame lowering the hammer block completely. It could be this has been gradually building up and your 45/70 barrel is just the "tightest" one in your set.

You should also be able to visually see the movement of the hammer block with a barrel off and pressing inwards with something like a brass punch or wood dowel under the shelf in the frame.

TC does say not to use any "regular" types of gun oil in the action. They recommend only a dry film lube that doesn't attract dirt and grit.

It is also possible, though I doubt it, that your hammer spring is starting to weaken, and your 45/70 bbl is the first one that shows the symptom.

[Dezynco]

Make sure the locking lugs on you 45-70 barrel are clean and lightly oiled.  If they don't snap into place, the pistol may misfire.  I've seen them drag against the bottom of the barrel, not engaging completely.