Even with a 4.0 this year I don't think my average over the years would be 2.5
Been there before myself.
Gun parts can be a decent side job. Guide rods for auto loaders, firing pins, thread protectors, small parts for obsolete guns like the old Stevens, Mossberg, etc.
I've been in the gun business for two years, so take this with a grain or two of salt. Products in this industry, in order to sell and keep selling, have to be perfect in every respect. That means quality materials, design, execution. No tooling marks, perfect finish. The standard is set high. If you can reach it or exceed it, great. If not, it isn't for you.
Look at Nikon, Leupold, Burris. If you can't make a scope that looks that good, it isn't worth the business plan. If you can't make an AR15 upper that looks as good as a BCM, you won't sell them for the premium they do as a barreled upper. Quality sells.
Another thing about bringing products to market. Retail is nice because the net profit is all you. Wholesale is nice because you make money on volume. Your per unit price is lower but, in my case with ammo, I'd rather sell 20K rounds to a gun shop on one invoice and make a few hundred dollars that sale then sell a hundred boxes of 50rds each. The key in this industry isn't retail, it's wholesale. Dealer direct wholesale is gaining ground. When you can fill orders for a few hundred units, distributor sales might be up your alley. A great distributor for gun parts is Numrich aka e-gunparts.com. Take a look at their online catalog at parts that are rarely in stock but fairly easy to make. If you can make a bunch of those parts with quality and in volume without giving up quality, market them to places like that.