rough idle and dwell angle for M115

what happens if the dwell angle adjustment at the contact breaker gets smaller? or larger for that matter? is there some ballpark way of replacing the contact breaker without a dwell meter?
i'v also replaced the distributor cap and rotor abt 2 months ago but apparently, the contacts seem arced already. this can't be normal right? could a badly adjusted contact breaker be the cause of it? tks.