Actually, the US civilian market is very big (heck, consumption of ammo is above 5 billion rounds a year). Enough that FN has been pleasantly surprised by demand for the PS90, civilians are snapping up SCARs as fast as FN can make civilian models above the demands of the military (they made lemonade out of a batch of aluminum receiver parts that had been anodized to the wrong shade and sold them as a special edition).

The nationwide sweep of shall issue concealed carry licensing has sharply increased demand for carry handguns. While people like me are happy with modernized M1911s for full sized guns, others aren't and new popular models are still coming out. Probably the biggest explosion is in "mouseguns", small .380 or 9mm handguns that are easier to conceal, especially in the summer. Many new models have come out recently.

I'd say the area of "black guns" (widely construed, not just AR-15 derived) is pretty healthy. Lots of stuff happening with AR-15 pattern guns (including driving them with pistons), lots of people looking for alternatives and various companies are delivering in one way or another.

Compared to aerospace, there's got to be hundreds more companies that someone could go to work for. Aerospace went bust in the early '70s and never recovered. The US civilian firearms market may be iffy as the economy continues to sour and the Democrats continue to treat gun control like a new third rail, but I'd sure pick firearms over aerospace, if for no other reason than there being such a range of OEMs (in sizes, from garage sized outfits to giants like FN, S&W and Ruger).