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Hi all,

I have decided to bush the firing pin hole on my "Custom action" that I've had for just over a year. I've had primer issues since day one all the way through the pressure curve and deciced to pull the bolt apart and do some checks to find out what i was dealing with. 

Having mic'd and clocked all the internal parts of the bolts and firing pin i have run into a few issues:

  • The firing pin hole is off centre by .2mm which when chucked up and examined is very noticeable. I'm not too bitter about this as bushing it properly will sort this.  Not the most impressive for a £1500 action though...
  • Firing pin/hole tolerance: Having mic'd the firing pin and pin gauged the holes there sizes are 0.067 for the pin and 0.072 on the firing pin hole leaving around 5tho of clearance. This is where i think the main issues of the crating is coming from and as far as i'm concerned significantly more than it should be.
  • Bent firing pin: This is the part that is causing me the biggest issue. If you look along the pin itself there are at least 3 separate cutting operations leaving 2 obvious parallels that are nowhere near each other in terms of concentricity.  i.e half moon cuts along the pin assembly . There is also significant run out over the 5mm end section of the pin its-self that you can see in the images. I have attached 3 images; One of the bolt in a "true" section of the bolt about 0.0024mm or 0.00009" runout. (This is the closest i could get without actually taking the time to adjust it) and then showing the bent pin. The very end of the pin showing almost dead nuts with the true section. But when you move 5mm up the pin this thin opens out to 0.01mm or 0.0004' 3tho run out in the space of 5mm. I drilled a sample 0.067" hole in some hardened steel to see how the pin would clear and sure enough the pin binds around 1/3 - 1/2 down.

Any suggestion on how to approach this? Obviously with the assembly being bent the pin needs significant clearance in order for it to work but this leads me back to square one. One thought is to precision grind the whole pin down to 0.0062 and got from there. Or, manipulate the pin to relieve the warp? Any advice is much appreciated. Thanks in advance

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How are you holding the pin - looks a long way out of the chuck to me - thus increasing run out.

 

The pin - for small diameter should be .062" , the bolt hole .065"

 

Id also consider extending the length of the firinmg pin turned diameter (.062") to allow the pin to run inside whatever bushing you make and fit within the bolt face so its encapsulated on cocking and firing at all times.

Would be interested what make of action this is - happy to recieve PM on this.

The pin you have in the images looks like a standard PTG machined piece by the way - easy to replace  - consider their lightened ones.....

 

You can machine the pin diameter quite easily in the lathe with proper tool and light passes

 

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16 minutes ago, Ronin said:

How are you holding the pin - looks a long way out of the chuck to me - thus increasing run out.

 

The pin - for small diameter should be .062" , the bolt hole .065"

 

Id also consider extending the length of the firinmg pin turned diameter (.062") to allow the pin to run inside whatever bushing you make and fit within the bolt face so its encapsulated on cocking and firing at all times.

Would be interested what make of action this is - happy to recieve PM on this.

The pin you have in the images looks like a standard PTG machined piece by the way - easy to replace  - consider their lightened ones.....

 

You can machine the pin diameter quite easily in the lathe with proper tool and light passes

 

Hi Ronin, Ideally I'd have gripped it up against the shoulder but as you can see: *picture attached* it's near impossible to due to the machining overlap that's been left behind. There's 4 separate surfaces over the space of about 10mm when you break it down. Where I've worked out all the dimensions the the pin retracts around 3.77mm and was going for a 4mm bushing. As it stands the pin already runs inside the hole apposed to leading in via a cone. 

I wish it was PTG. I've sent you a PM IN regards to who made it.

 

 

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Hi

I had similar issues regarding firing pin when I used a .308 Ssg action for a 6.5x47 build as went from large rifle primers to small and I ended up with "primer flow" around the pin.

I used Neil mckillop and he done a fantastic job of bushing the pin.

Good luck

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+1 on Neils work... did the same job for me.... cured my primer cratering issue.

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