Another update, I went to the range on Sunday with two batches of ammo, both using the same powder but diffrent primers (Remington 9 1/2M, and Fedral GM215M but a different batch to last time) I had seated them a little more gently than last time to make surre that i was not crushing anything.

The Remington primers would not go bang for love nor money, but the Fedrals all went off ok this time. I'm off the opinion that the pin is striking the primer on the lower limit of "just hard enough" so as i have seated the fedrals a little (and we are talking a max of 0.02mm diffrence here) shallower than last time it is just enough to make it go bang.

Simon