pierced primers

[AusFclass]

hi guys!
i have a BAT M in 6.5x47 Lapua and whilst working up loads i notice that the primers start to extrude into the firing pin hole at relatively low pressures. in the past i have reluctantly run at a much lower node but have now been forced to change to a different projectile that seems to only run well at higher pressure.

i use cci standard small rifle primers as i was under the impression they had the hardest cups out of all suitable primers.

the primers do not have a sharp square outer edge and there is no stiff bolt lift at the load level that the primers have pierced.

it has been suggested that i investigate the possibility that the firing pin itself is too large for the small rifle primer. i was unaware that the diameter of the pin would cause this and thought the clearance between pin/hole, radius and the protrusion would have more of an effect.

i was not aware that there were different size firing pins for large and small primers.

is anyone able to shed some light on what the ideal pin/hole dimensions should be or is there a harder primer that may be suitable?

 

[RMiller]

I also have a Bat M but on a 6x47L. I get the same thing from time to time. I use cci 450 Magnum primmers and only see it on very heavy loads. Try the magnums. As far as why it is happening, I believe it may be caused by the very light firing pin spring in the Bat's. But that is only my quess. To light a spring lets the primmer push the pin back into the bolt.

Ryan

 

[Robert]

I also have a Bat M but on a 6x47L. I get the same thing from time to time. I use cci 450 Magnum primmers and only see it on very heavy loads. Try the magnums. As far as why it is happening, I believe it may be caused by the very light firing pin spring in the Bat's. But that is only my quess. To light a spring lets the primmer push the pin back into the bolt.

Ryan

Ryan,

A weak spring and a too large diameter firing pin tip can effectively allow the FP to slightlu 'blowback' under high pressures. This happens on both LR and SR primers, but is more common on SRs.

Normally, the FP tip for a SR primer is smaller than for a LR,.065 for .080 most common), but the protrusion is also smaller,.055 to.060 for.060 to .065)

As the SR primer need less indentation depth than LR to ignite, the firing happens when the FP tip has not fully oobstructted the FP hole, and the gap created around the FP tip radius allow for craterisation, cup metal dilling the gap created.

Converting actions for LR to SR primmer caliblres does not mean simply chage bolt heads, it also need changes of FP tips sizes.

Now, some actual competition actios uses with great success the small diameter FP for both LR and SR. This no doubt for me reduces igntion time.

My point only, FWIW

R.G.C

 

[wwbrown]

The 47 L is hard on primers they will crater at low pressures and it is hard to use the crater condition as a pressure indicator.

My go to primers in SR have been BR4 but I am running low so I picked up some Wolf magnum SR, they are the same as the non-magnum except have a stiffer cup. They are a bitch to seat in new brass but the cratering is less, it is still there but less.