When a couple of my 24/47s were having trouble igniting the primers (my own fault) I made sure that the insides were free of old cosmoline. That solved the problem here. Other folks have had to get new springs that were more potent. Some ammo also seems to have harder primers too. Best of luck.
You can also check fp protrusion though I doubt it'll be the problem. The others have given you the most likely source of trouble.
Anyway, it should be .055-.065 inches. As noted, it ain't adjustable. If it's long you can polish it down. if short, you can only replace it.