misfireing rifle

[English]

Hi I have a mate who has had a rifle built in 260AI,its all seemed fine for the first 100 fireforming rounds,I reloaded some test batches for a full AI load then the problems started.
we kept getting miss fires,i changed the primers,still the same,I changed the batch of powder,still the same.
in the end after speaking to a few people who had had a similar problem with the internals of the bolt having too much grease inside which can slow the firing pin down.
we cleaned all the grease out applied a very light film to ther spring (after changing it) all seemed fine,the rifle didnt misfire.
all seemed well problem solved,it wasnt,my mate was on a trip in Scotland and lined up on a deer and had another miss fire
so my question is has anyone got an ideas to throw my way of what it could be.
the action has been made by a company in the UK

 

[Larryh128]

Really impssible to tell without seeing the action BUT it really sounds to me like you are on the edge of the firing pin protrusion. If the brass is snug, it'll probably fire OK, if the shoulder is set back a couple thou ???? Different actions need different firing pin protusions but MOST are around the .060 range. Check it, if you're closer to .050, that COULD be your issue.

 

[wapiti25]

Check the headspace on the ammo. The shoulder may have been set back too far during sizing.

 

[English]

update
the firing pin only comes out 43 thou so this seems to be the problem

 

[Larryh128]

I think that you have found the issue.

 

[boltfluter]

Replace the firing pin spring. Paul.