The number one rule of applying for a patent-- any person who“invents or discovers any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof, may obtain a patent,”
In other words, don't underestimate the patent value of what you are doing. My 2 cents.
To answer your question about how big is the market, the market is billions of dollars (just in America alone)--grab a piece of it man. Rule of thumb, "build for the masses, eat with the classes; build for the classes, eat with the masses". There is a larger market for cheap firearms.