Curious Ive got a 70 ASP four stroke in mine which is probably 140 grams heavier than your magnum 52 and to balance it the battery is installed behind the servo tray, I am suprised that yours does not balance with the battery right forward under the tank. The c/g should be 4 & 5/8" behind leading edge of wing adjacent to fuselage. Useful weight can be added to nose if required by using an alloy spinner instead of kit supplied one. If you have to add more weight make sure its firmly attached to bulkhead of model with sheet metal screws, epoxy or silicone.