Instead of "keep your powder dry," it's "keep your caps tight," eh?

And the powder from going out.

And AFAIK their living on a desert world of sorts, so wet powder is unlikely.

Well, even the worst desert has a monsoon occasionally, so...

Or gun nuts salivating over the gun?

Quite!

Actually, there are deserts that have never had noteble rain for centuries, if not longer. And our Fehnniks are not restricted to the desert, but they do prefer it. Has a minor fannish though about a failed colony in the tropical equatorial mountains and coast beyond (in my fannish version of the world- large single supercontinent on most of the northern hemisphere, a portion of the southern edge straddles the equator)

(nodnods) Gotcha!

Percussion flash holes can be much smaller than the grind of powder, so that isn't a problem.

Ahh, cool.

Very interesting.

When could something like this have been invented in the conventional "timeline" of gun development?

While in RL, it was a novelty during the percussion era, in an alternate scenario, there could have been a matchlock version before. Then, later still a breech-loading pin-fire cartridge version. In my version there would also be a period of piezo-electric musket ignition.

Neat, but wouldn't the flash/gas escaping out of the nipple start hurting the finger after a few shots?

An interesting question. I'd WAG that a more cupped hammer would deal with most of that, and any escape would be more planar and miss the finger.

Or the soldiers wear gloves as part of the uniform...

Don't think it would be much of a problem, though wearing a finger guard would make sense. Fumbling around to replace a cap under pressure needs all the nimbleness uncovered fingers can manage (been there, done that). And just thought, the finger guard could become a sign of a musketeer/rifleman over time.

I would think that a cupped nipple, and a heavy hammer would protect the fur of the fingers and etc. Kind of like this:
http://3.bp.blogspot.com/-PI9CtmLio.....mer-Nipple.JPG

Ohwow. What an action.

Just dawned on me that it was my experiance that the only real issue with most percussion cap systems is the cap itself disintegrating, rather than any back pressure or flash per se. The cap would often split on impact, but the flash jet, if any, was pretty insignificant. However, once in awhile, a cap would fragment, and in that case, the flying bit were something of a hazard. The deep cupped hammer would pretty much deal with that, however.

Interesting design - though I'd be a bit worried about the possibility of the cap falling off if the gun was carried in a rough way. Though I guess if it was a tight fit, that could be avoided.

Spoopy action. I wonder if anything would go bad with the cap and your finger being right next to it. I'm not a blackpowder guy, so I wouldn't know.

Thinking about the design a bit later, realized a more cupped hammer would easily contain cap fragments and/or ignition jets. The actual main charge ignition wouldn't blow back through the touch hole enough to budge the hammer in any case. The main hazard to one's finger would be from the cap. Without a containing cupped hammer, there would be a risk of exploding/fragmenting caps (an occasional hazard even in conventional percussion actions, the hammers usually have some cupping, but not always enough, I got hit by fragments in the face once when firing in ranks)

That sounds fun. I've thought about getting a black powder revolver for some time now.

I've got several, but have never gotten around to shooting them as BP is so damn messy and absolutely needs to be totally cleaned out. I really like my 1861 Springfield replica, smoke and boom and big .58 slugs down range. Fairly simple to clean as well. I'd still like to build an underhammer musket one of these years.