Well it sounds like you'd be more interested in a flex type shooter like a splattershot pro, a gal or maybe a jet squelcher. What's super important about any weapon class is movement and aim. You don't want to be too predictable, and you want to be able to track targets for however many shots it takes to kill them. What you might be struggling with is that you usually play 1HKO weapons where you just have to get them at one moment and they're dead, whereas with shooters you have have to be consistent in hitting them multiple times (granted it's really not a huge challenge because of the high fire rate). In order to learn a completely new weapon - take it into turf war (or league) until you feel you've improved on using it and feel more comfortable. Personally, I recommend that everyone learns how to play the splattershot or the tentatek splattershot especially if you're taking on shooters. However I realize this doesn't fit your comfort zone. But I also think everyone should try (I mean like actually try and spend time on) every different role in the game. BUT ANYWAYS. As for learning, try all the shooters in the firing range and spend quite a bit of time in there to work on aim. I always say "the firing range is your best friend." Then take a few of your favorites into turf war. Then look up some videos on youtube or find some people who stream the weapon you want and take it into ranked paying attention to how they move and what they do.