DITCH hows things,
firstly give the rifle a good cleaning out with bore solvent, a good clean with a touch of oil on a patch, then put dry patches through the gun to clean out the excess oil, the gun is second hand, who knows how well it was cleaned, could be a slight ammount of copper in the barrel, this will effect accuracy something terrible,
so a good clean to start, don't worry about the trigger yet as you've only just got the rifle, practice is the key, and only then if you still find you can't achieve good results at 100 yards, say right an get the trigger lightened, i'd say 2 pounds