Ballistics simulations could be a big one. More technical literature on how to design things like machine guns and complex operating systems would be helpful also, I think the most comprehensive I've read on the subject is Chinn's The Machine Gun but it's pretty old these days and doesn't cover some new stuff. 3D-printed and homemade gun scene is big and getting bigger and that's def got overlap with tech. Especially since it tends to get booted from mainstream platform and has mostly moved to stuff like LBRY and Rocket chat, helping to keep it up in the face of gun-grabber censorship would be good. Or using tech to expand the reach of gun-rights activism and make it easier to design, modify and print 3d-printed guns. Tons of ways if you want to get involved.