Aprilia Man
I have 30-30 cases over 25 years old and full length resized countless times and only die from split necks and never from case head separation. On the flip side of this I have seen Winchester .303 British cases start to separate "if full length resized" the third time they are reloaded.
As Eagleye stated above high pressure and excessive full length resizing will shorten your case life. If you full length resize using minimum shoulder bump (.001 to .002 shoulder setback) your cases will last a very long time.
We live in a plus and minus manufacturing world and if you have a chamber on the long side and a resizing die on the short side you can over resize your cases "IF" the die setup directions are followed. Meaning if the die is making hard contact with the shell holder you "may" be "over resizing" your cases.
If you get a Hornady cartridge case headspace gauge you can measure your fired cases and adjust your dies for minimum shoulder bump (shoulder setback)
Below is a fired case from my AR15 carbine.
Below is the same case full length resized with the shoulder pushed back .003 (shoulder bump or shoulder set back)
Below is an exaggerated illustration of full length resizing, the distance you push the cases shoulder back between the red and green dotted lines will effect your case life and how much the case can stretch when fired. If you keep your shoulder bump to the minimum the case will not stretch beyond it elastic limits and last much longer.
Below are just some of my .223/5.56 dies and I said we live in a plus and minus manufacturing world. I have a standard Lee full length die that will size the base of a .223/5.56 case a smaller diameter than my RCBS small base die. This same Lee die will push the shoulder back .009 shorter than the GO gauge, meaning .012 shorter than my fired cases if the die makes contact with the shell holder.
Below, these cases were fired in a brand new Savage .308 and reloaded over and over till the cases failed. Also note the shooter just wore safety glasses and was not hit or injured by escaping high pressure gas.
The problem is the rifles actual headspace was not given and the die was setup to make hard contact with the shell holder. Meaning the actual shoulder setback was not stated so your mileage will vary.
If you were to run this same test on a M14/M1A with its longer headspaced chamber and .002 larger in diameter the case life would be far less.
In over 46 years of reloading I have never had a case head separation and the key to my luck is minimum shoulder setback and reasonable chamber pressures.
Below using a RCBS case mastering gauge to check for the cases thinning in the base (super bent paper clip that measures in thousandths )
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