What’s the cause?

[Usaf197]

BLUF: CDG with PVA 25x47 having failure to fire 7-12% of the time.

Potential causes I can think of:
1. over pressure on load causing black primer strikes (see photo) melting primer material on to firing pin.

2. Pivoting feature on CDG bolt? Haven’t tried non pivoting, running a TT Special at 1lb 2 oz. I’m only aware that running a light trigger (TT Diamond etc) can cause issues but I don’t know what type.

3. Firing pin assembly issue? This failure to fire isn’t consistent. It is almost always after I get a pierced primer or black primer strike (see photo) if I’m calling it the wrong thing. I can’t see any issues on the surface of the firing pin but maybe.

Background:
90-92 degrees out but also had this issue when it was approximately 80 out.

Load: Berger 135 long range hybrid.
Shooters world precision at 37.4 gr with both cci 41 and 400s.
H4350 at 40.4 gr.

I have been above both of those load numbers by about .4-.5 and felt a little tougher bolt lift and backed it down. Even at the higher chargers this issue wasn’t consistent.

Any ideas as to the root? I appreciate it. Going to reach out to ARC as well


The photo with the 2 metal dots in front of the piece of brass is from when a black primer strike happened and it came out with the firing pin or got stuck in the flash hole of the bolt head.

The photo of the 2 pieces of brass is the metal not coming completely off of the primer with the firing pin.


This load was consistent with an SD of 4.8 for SW and 6.2 for H4350. I think that rules out a random higher charge causing it.

 

[spife7980]

They are called punctured primers. It’s sending a jet of plasma down the primer and into the bolt face firing pin hole. Stop after one and fix, don’t keep grabbing the tiger by the tail.

Don’t use 400 primers, they are thinner and more easily punctured.

I can’t see much of the fuzzy firing pin but it likely popped a 400 once and the jet of plasma deformed it a bit making it more likely to puncture again, a vicious circle.

If we look at shooters world 6x47 and 6.5x47 load data with equivalently heavy for caliber bullets and interpolate, you’re over their max loads.

Max loads on thin primers is a recipe for this situation.

 

[Usaf197]

They are called punctured primers. It’s sending a jet of plasma down the primer and into the bolt face firing pin hole. Stop after one and fix, don’t keep grabbing the tiger by the tail.

Don’t use 400 primers, they are thinner and more easily punctured.

I can’t see much of the fuzzy firing pin but it likely popped a 400 once and the jet of plasma deformed it a bit making it more likely to puncture again, a vicious circle.

If we look at shooters world 6x47 and 6.5x47 load data with equivalently heavy for caliber bullets and interpolate, you’re over their max loads.

Max loads on thin primers is a recipe for this situation.

So the easy fix dial back the load and buy a new firing pin?

 

[spife7980]

I can’t quite tell from the pic, but backing down would be my first step, you may find with cci41s and less powder that the issues goes away. If not and the tip is gnarled, new pin.

 

[4O6shootist]

Carbon is likely blasting down inside the bolt body, some is probably accumulated inside the bolt/fp hole, reducing the energy of the pin falling causing the light strikes. The hot plasma gas will eventually etch your bolt face and eat into the fp hole as well as the pin itself. The pin will get gas cut and rough, causing liklihood of even more pierced primer. These pressures often travel the bolt down down into the trigger housing, causing trigger damage. Don't do this!

Cci400s suck for performance bolt guns. Switch to 450s if possible.

37+ gr varget equivalent may be a bit stout in the 25x47, 37.2 gr was getting spicy in my 28in 25x47 at 2780fps.

 

[JerkyFreak]

Those little disks detach and interfere with the firing pin strike.

Usually caused by a firing pin tip that does not have enough of a radius, i.e. a flat tip. It should have a rounded tip. The flat tip works as a punch resulting in nice round holes. Get the gunsmith to round the tip and smooth it out.

Take a better quality photo of the firing pin tip.

Another cause is if the firing pin hole is overlarge. Some Howa bolts are known for this. When shooting stout loads the primer protrudes so far into the bolt that it shears off and stays inside the pin channel. To fix, either get a bush installed or get a firing pin with a larger diameter pin.

Take a quality photo of your bolt face with the firing pin protruding.