I was out shooting my 243 today with my daughter to get ready for deer season and after some of the shot I noticed that a couple of the cases the necks were split at the junction of the shoulder. This is the second time these cases have been fired and this gun. I partial resized them and they are loaded with 39 gr H4350 and a 95Gr Hornady SST and WLR primer in a Winchester case. The are grouping well, but it seems to me something is wrong that the cases are failing this quickly. I am open to any and all advise. I have never seen this happen this quickly before in any of the other guns I reload for.