Today got the spring made and fitted.  Still a little harder to open than what I want in the end, but it's an easy fix since I made the spring heavier than I thought would be needed.  I'll just thin it.   Also need to make a correct screw at some point, the one I used here was a reject, from another project, that I still had laying around.
Bob

Thanks Bill!

I started setting the box into the wood stock today.  Many of you have seen how I do this but I will cover it again anyway in case anyone might be curious.  Before starting the part needs some work done to it.  In this first photo I'm showing the beveled I file to the bottom edge.  

This little angle allows the knife, used to make the outline of the part, to get in under and inside the edge.  Photo 2 shows the box set into the wood to just flush so the bottom is mostly tight against the wood.  The features on the bottom of the box are the only thing inlet, at this point I run the knife around the edge.   
In case someone with good eyes would see it, the back of the box is set slightly above the centering line, but the front is centered on the line. This was a running change that seems to happen often!  I decided I liked the look better with the back slight higher than what the plan originally was. 

Photo 3 shows the the knife cut around the box showing it's position and outline on the wood.  Because of the beveled edge on the box this line is just inside the edge of the box.

Fourth picture.  Once I have the outline of the part on the wood, I next stamping a line, just inside the knife cut line.

Photo5.  I then start taking wood out to the inside of the stamped line. 
Never said I was good or even neat when inletting a part...as can be seen here!
Bob

So now starts the reason why I stamp the line inside the knife cut line.

In this first picture, at the lobe on the left, you can see where I have stabbed straight down into the knife cut line with a gouge, and how the wood broke cleanly to the inside.  With the wood gone to the inside, the chip is free to move and break off that way, which gives a nice clean outside edge to start final inletting of the cap box.

It's important, as you stab in, to go the correct direction so the wood doesn't try splitting out through the inlet the wrong way, which can happen in some wood spoiling an otherwise nice clean edge. In this second picture you can see the wood breaking correctly in this long grain.

I'm moving along in this last picture, working areas that I'm fairly certain how the wood will break free.  In the areas where I'm not sure, I cut in very shallowly, without chipping the wood out, working the full length of the questionable area.  I then go back over it a couple more times until it breaks free.  The is the process I used along the top edge in this picture.
Bob

Bob, I've found that the shape of these small chisels really work well for the kind of inletting that you're doing.  Great for lockplates and patchboxes and getting through that gnarly walnut.  One is an 1/8" and the other 1/4" wide.

I assume you made them?

I bought the same pair of chisels some 50+ years ago from either DGW or Brownells.  I've only used them a few times over the ensuing decades; but like Old-Win I can attest that in certain situations, especially with figured wood, nothing else works better.

Bill Lawrence

I bought mine maybe 30+ yrs ago from one of the small mom & pop muzzle loader suppliers back in the day. The didn't come with handles so had to make my own.  Used them on my Hawken and York rifle and inletting my high wall stocks.

The cap box is done really nice and the great Inletting. That’s one thing I’m not very good at and thanks for the tutorial showing us how you did it.

Not sure anyone will find this info interesting, or even useful, but I will show it anyway.

A gun seems more complete if the screws are all indexed.  I never use to pay much attention to this but anymore I do like the look when the gun is finished.  So how does one index screws?  There are probably lots of ways to accomplish it, this is the way I do it, and it seems to work.

In photo 1, I originally leave screw head long with a hacksaw cut slot for  a "working slot". Here I am showing the lower butt plate screw.  It is tight and coated with Dykem layout fluid.  I then scribe a line around the screw at the butt plate.  Then scribe a line that indicates the new slot position.

Photo 2, Once the screw is removed I extend the line below the scribed line that indicating the butt plate surface and the shortest the screw head can be.

Photo 3, I mount the screw in a 5c collet indexer, which is mounted in the mill.  I have both 3 jaw collets and 4 jaw.  If a 4 jaw can be used with a screw size, it make it easy to set up.  A 3 jaw take some extra care.  I use the slot between the jaw sections to align the scribed mark.  The saw cuts a horizontal slot, so one of the collet slots needs to align "the same" in the indexer.  The 4 jaw does this automatically but not the 3 jaw, so I simply use a machinist square to line it up off the vice jaw. 
Bob