I can find 70% isopropyl more readily and use that sometimes. I also use the alcohol swabs that are supposed to be 70%. When I did find a bottle of 90% I bought it and it worked about the same as far as cleaning. I use an air compressor or bottled compressed air to blow the gun dry after a final cleaning so it probably doesn't matter. For swabbing between shots either does it, as I have used spit with no ill effects for the same purpose. The "before shooting" you mentioned is to get any oil or water (moisture) out. The evaporation helps remove the moisture so the 90% has a little more evaporative effect but the patch itself and the motion of swabbing is also displacing moisture. I have poured a capful of either potency isopropyl down the barrel and shook it up (with my finger over the nipple or flash hole). Turn the barrel over and let any remaining run out. Then blow air from nipple or vent hole. That gets into the breach and the deepest part of barrel where the powder will be.