Pommy Chris wrote:Simplest way to see if a case has headspace in a given chamber is make up a 2 thou shim and put it on the bolt face then clip the base of the unfired case onto the bolt and insert the case shim and bolt into the chamber. This is done like this so the shim does not fall off. If the bolt is firm to close then you have 2 thou or less headspace if it is easy to close then you have 2 thou or more. If more repeat with another shim added and another until bolt wont close or is stiff to close. I had one shooter who had issues ages ago and I had about 8 shims in there so clearly headspace was his issue. With shims in though dont pull the trigger or the firing pin buggers all your shims up. I usually have shims in my gun box just for this test. Another check you can do is ensure primer is seated enough ie all the way in the pocket. If not the firing pin looses strike energy pushing the primer forward the primer is not seated all the way in.
The shim test is rough and ready as cases have some spring, but if you have 4 though of shim and you just get resistance ie about 4 thou headspace rounds should be going off, more I would be starting to be blaming headspace as a possible issue. Most saami chambers with lapua brass (palma) are 2-4 thou that I have measured in this way.
If chamber is saami specs lapua brass should not give headspace issues ie prevent round going off.
Chris
The shim idea is a good one ! But if one doesn't have access to shims , one could use a piece of celo tape , which is approximately 2 thou .
I still haven't figured why I've had troubles with the 280 ackley with correct head space ! Starting out with 30-06 brass and not knowing what to do , was the main cause of the problem .
But I had an odd one not go off and when I got home , checked the head space with the firing pin out and was correct but still that case didn't fire !!??
I've put the 280 Ai on the back burner for now , but suspect something is going on with the primer pocket not being square . I'm using Cci primers and in the .284 or 7-08 Ai no miss fires !!???