Annealing a spring sounds simple. It most certainly is NOT... Springs are so small that reaching and holding the correct tempering tempurature for the required time is difficult, plus you have to guess at the material used in the spring. Making small springs is not easy, it can be done but is not easy.. In any case the problem you describe is not a spring problem. The feed lips of the mag should be a bit closer together to hold the round down until caught by the bolt. If the spring is in the magazine body in the correct attitude, it is very likely doing what it needs to do. The feed lips on the other hand often need minor adjustment to feed just right. On bolt action magazine(detachable) rifles this is not too hard. Use bar nose or round nose pliers. I use some made for bending wire into loops in electrical applications. Smooth the lips, not grind, not polish, just smooth them a very very little bit. The height the mag is held in the rifle and the feed angle(as set by the feed lips, are all that usually need any adjustment..