I took my S&W 686 to the range yesterday for the first time in probably 6 years. It shot very well until near the end (about round 40-45) where it had a misfire. The primer definitely had a smaller firing pin mark than the other rounds. I retried the round and it fired fine. This happened again around round #50. Ammo was Atlanta Arms and Ammunition reloads that the range sells. The gun has a spring kit in it so here are my questions:
1) Would this be more of a mainspring issue or a hard primer? I ask because the frequency is low (4%), though too high for a defensive weapon (this is more of a range gun).
2) Is there anything that can be done to correct this that would not involve changing the mainspring? I know that is the easiest solution but the DA pull is REALLY sweet so if something else could be done I'm open to it.
I know what I'm probably going to have to do but I'm wondering if there are other options. Does Atlanta Arms and Ammunition ammo tend to have hard primers? My Kahr didn't have any problems with their 9mm but it is bone-stock (and scarily accurate BTW).