I just put together a cider and I realize it's got like 3-4 weeks until I bottle but my question is this. When I bottle a 5 gallon brew I use 3/4 c of corn sugar in 1 c water. Will that work for 4 gallons of cider or should I cut back on the sugar some to account for a gallon less to prime. Don't want bottle bombs.

use the calculator on this site and you should be spot on. Just guessing but you would overcarbonate if you decrease your volume by 1 gallon and still use the same amt of priming sugar. Cider isn't any different when priming vs beer.

Don't measure by volume for priming sugar. You can do it 10 time and weigh each one and be off by well over 1 Oz. I aim for .8 an d1 Oz per gallon of beer, I'd do the same for the cider if I conditioned it in the bottle.