Oldwood's idea makes sense but "cut out the squirrel image" is far easier than it sounds.
I mentioned in a previous post that I taught jewelry making for over 15 years at several local arts centers. So from my experience may I offer the following:
Sawing (using a jeweler's saw/frame) is not the easiest skill to pick up. If you want to tackle it I would suggest that you visit some jewelry making sites and do a bit of research before you try it (watch some videos) and saw some scrap prior to the actual job. But here is a thumbnail sketch...
Basically you would need a jeweler's frame (I would suggest a saw with a small depth, 3" saw would be a nice start) Amazon has a 3" frame with a blade assortment for under $15. I probably would not trust their blades, if you buy cheap blades (which these probably are) they often do not have a set and are basically uncontrollable. You would need a bench pin to saw on. You can make this yourself out of hard wood. Mine is made from a piece of Madagascar rosewood but any hardwood will do. Taper one end across the wide end of the piece of wood. Mine is about 2.5" wide and I tapered back about 3". You cut a "V" in that end and lock the other end in a vice.
The rule of thumb is to have 2 teeth of the blade in the thickness of the metal. I use mostly 4-0 & 2-0 blades. You will lube the blade when starting the cut and also as your sawing progresses. Candle wax is often used as a lube.
So you hold the metal down against the bench pin with one hand and saw in the cut out "V" area. If you decide to try this...you will break blades, everyone does when learning and even after. That is why they are sold by the dozen or gross. Major tips: hold the saw so the blade is perpendicular to the surface of the metal, do not tilt it at a forward angle unless you are making a long straight cut. Hold the saw handle very lightly. Use the majority of the length of the blade (do not use short up and down strokes, exception...very tight curves).
Actually brass saws nicely, copper is "sticky" and sterling silver is just a bit less friendly than brass. I don't recall ever sawing any nickle silver (German silver) but I would guess that it is very similar to sawing brass.
Probably more than you wanted to know but perhaps it will be helpful to other forum members. I can't give any black powder advice because I don't know any but I'm happy to contribute where I am able.