Sort of a bunch of questions all at once. Thanks for any input.
I've read quite a bit (here and elsewhere) about a few of these topics, but I have a few questions.
After splitting a neck on my .300 WM on firing it on the weekend a lot of questions arose... the split is longitudinal (i.e. not around the circumference), right through and is in the middle of the neck (i.e. not right through to the mouth or into the shoulder area).
The loads have been fairly middle of the range and this is the 8th loading of the case with no annealling and no apparent other problems. The 7th loading still produced good accuracy and SD's around 7-10 fps. Saturday was not chronoed, but (accuracy) results seemed really bad. I'm now guessing something on the neck tension was the reason. I'm inclined to toss the whole batch of brass, although I suppose it could be "one bad case". I only picked it up last night when I was getting set up to clean the cases.
Does neck tension go suddenly or is it a progressive thing? As the 7th load had velocities within about 5-10 fps from the 3rd is it fair to assume that neck tension was pretty constant until that point? In other words, as the cases age will neck tension change show up at the chronograph or how else can I check it is still consistent?
What type of case life should I expect with a factory chamber, minimal shoulder bumping and midrange type loads?
I'm sure I have more questions that will come to me as / if a discussion starts.
After 7 loadings my opine is your brass was wore out from being 'worked'. Neck tension had little or nothing to do with it. Each time you shoot a case the brass flows. A split neck is a common thing when loading high power ctgs, such as the 264 Win Mag that I loaded for 25 yrs. A lot of my splits w ere at the shoulders too and didnt always go to the neck. Working brass(resizing) dont make it stronger. Brass is like life...it's longest on day one, after that it's all downhill. I loaded some 264 cases 10 times, others 3 times. It's just a brass thing. Neck sizing helps extend life some, but it never worked good for me in any of the many cals I loaded for. Good luck.
Brass work hardens itself with each firing. So neck tension is a progressive thing.
On brass that is hard to replace, (tight neck chambers ect) I will anneal every 3rd or 4th firing. I use wilson seating dies on these guns and can feel when seating the bullets any noticeable difference in neck tension.
If it is a factory chamber, I would be inclined to chunk it and replace it. But annealing will prolong the usable life of the brass.
I think your inclination is a good one. Annealing will surely extend the life of your brass but you have gotten good service from it already. Time to let it go!
Doubt that varying tension is the cause of your loss of accuracy, except for sure the split neck round. That will surely put a hole out of any group!
Your neck split is a common type. The shoulder gets little work so it doesn't harden and split very often and the case mouth tends to be the softest part so splits generally occur between those two points.