Thread: Light Primer Strikes

Originally Posted by grandpamac

Greetings All,
As mentioned previously in this thread light firing pin strike and missfires can be different to a lot of different things but it can be due to a combination of things. One thing that was mentioned by @Moa Hunter was excess head space, This can be present in the rifle or it can be created in the FL sizing die. The OP mentioned the .280 AI as the problem chambering. The .280 AI chamber is shorter from the neck shoulder junction than the parent .280 Rem case. This is done so factory .280 ammo can be fire formed in the AI chamber. To convert a .280 Rem chamber to .280 AI the barrel needs to be set back a thread so that his junction supports the case properly. This takes extra work and I don't know how often this step might be ommitted. All of the other 06 based cartridges have shorter headspace than the .280 so other cases need a false shoulder created to support the case close to the bolt face when firing.
Recently I bought myself a Hornady Head Space Comparator. Measurements revealed that my old Lyman 6.5x55 dies were setting back the shoulder more than 0.010" from the fired position in my T3 and more like 0.015" in my M38 and a friends Ruger 77. New Lapua cases measured close to fired cases in the T3 so the problem was the dies. A new set of Redding dies and a Competition Shellholder were purchased but I found the Redding dies still needed the +0.010 shellholder to get the right amount of shoulder bump. The US standard dimensions for the 6.5x55 clearly differ from the original. There is a level of arogance in the US about things not invented there and the same situation may apply to other continental cartridge dies so be warned.
Regards Grandpamac.

Very interesting that the dies are out of spec and not the rifle chamber. Also interesting that there are +0.010 shell holders. What is the reason to use this shell holder instead of just backing the die off and setting locking ring ?

Greetings @Moa Hunter,
The dies are likely cut to US SAAMI spec but this is out of line with the spec being used in Finland. Unfired and fired Lapua cases from the T3 measure almost the same, both made in Finland, so I am assuming that the cases are max and the chamber is min. The Ruger factory rifle is longer by 0.005' so this would be a max chamber on the Finnish spec. Only the US dies are out of step.
Regarding the Redding Competition shellholders I find that these give a more precise sizing than backing of the die based on my measurements. I also have more than one rifle in .308 and 6.5x55 so the shellholders are a better way of setting the case headspace instead of having to adjust the die. My VSSF .223 is spot on with the standard shell holder and my T3 .223 needs the +0.002" so I borrow a shell holder from my son for any sizing for it. For My SAUM which I don't use mutch I will probably just set the die as you suggest.
Regards Grandpamac.