I've used the regular 'Scope for a while, maybe i can help??
-Practise a ton with the targeting dummies. Start off by simply shooting them, figure out how far you can be from the dummy before you'll get outranged. Find a sensitivity setting you're comfortable with. The scoped chargers have longer range(generally considered to be better), but vanilla chargers have improved mobility.
-If you can consistently hit targets, practise moving while sniping. If you can manage that, quickly sweep your view over the dummy and snipe it in one quick motion. You unfortunately don't have moving dummies but you can improvise.
-Keep your position in mind. You can't do a thing to people behind cover(obv.) but it's also hard to get rid of people directly below your perch or people above you. Keep a close eye on your map so you don't get shot in the back. Paranoia is your best friend.
-Without main savers, you'll have 5 full charged shots before you'll need a refill. If you use a splat bomb you'll only get one(correct me if i'm wrong).
-If people see you're wielding charger, keep yourself hidden (esp. against to E-Liters which outrange regular chargers). Don't rely too much on your splat bombs to do your work for you. If a good E-Liter knows you're there they'll keep an eye on you and won't let go. Other people will start piling subs on your perch.
-If you get splat don't return to the same position unless you really have to.
-SJ back to base if things look bad, toss a splat bomb at your feet if you know you're gonna get splatted. It might just give you a trade!
-On the same subject, change your location regularly, it's much easier to snipe people if they don't expect/see you. While high ground will give you the range advantage you'll also be a lot more visible.
-If you can't see anyone yet try using your map to find enemies.
-Stay away from enemy ink. If you have to, try to keep map control by inking turf to keep it safe but you'll have to keep in mind this'll reveal your current position.
-Also, use Cold-Blooded. You don't want to get tracked, especially not as a charger.
-Don't let Splat Bombs do your work for you. You're still a sniper. Use it to splat/move enemies you can't hit as a sniper but have little trouble hitting you. Roll them by aiming them to the ground to shorten their fuse. Keep in mind splat bombs will always have a big minimum range.
-If your special is ready, use it to reclaim turf or scatter enemies. Be extremely careful because you're a lot more vunerable than you look. If someone tries to close in on you, start backpedaling and roll bombs, the enemy will likely get stuck in the trail of explosions and get splatted for it's trouble. If things are really bad, stop your special and leave.
You can also watch streams of people playing chargers, some of them are really good and you might learn a thing or two from them.