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Primer Reading

 
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  #1  
Old 02-19-2007, 07:44 PM
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Primer Reading

Need a little help here....I was having a little bit of primer cratering on my 243AI. It was happening even with the fireform loads, so I figured it was the firing pin. We looked at the firing pin and it measured a little undersize, and the hole was beveled. We drilled the hole out so the the Holland pin would fit. Problem solved, so I thought. Now, I get a raised protrusion on the primer. It looks like the primer is flowing back into the firing pin hole. Still does it even with the fire from loads. Dave Kiff suggested to slightly flatten the firing pin and that would probably cure it. First shot, primer looked perfect...second shot, slight cratering....third shot, slight cratering w/protrusion. I am at a loss here. Do I need to go up in the powder charge? Change primers...it had been working fine (except the slight cratering) up until we changed the firing pin. I am using CCI200 primers...remington short action, Lilja barrel.... [img]/ubbthreads/images/graemlins/confused.gif[/img]
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  #2  
Old 02-19-2007, 10:42 PM
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Re: Primer Reading

what are your fire forming loads?
A severly reduced load can cause pressure problems especialy if the gun is not pointed slightly up of shakken when its pointed up before firing.

How much firing pin protrusion do you have when the sear is relaxed?
If you pin is sticking out to far it will show signs of cratering where the primer is trying to wrap around the pin thats sticking out to far. In some extreem cases it'll pierce the primer

I assume that the chamber is cut correctly? A true Ackley improved chamber is acctualy a bit shorter than standard causing a slight crush fit ,if this is not the case then you might be having some head space issues where the firing pin acctualy bounces the case off the bolt face a tiny bit , generaly this results in the primeres looking flattned out but it has shown to give cratered primers depending on the primer used.
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  #3  
Old 02-19-2007, 11:11 PM
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Re: Primer Reading

JD,

My fireform loads are 40gr of H380 with a 100gr bullet...Headspace is good, and there is a slight crush fit. The firing pin is protruding .050. The factory firing pin hole had a slight bevel around it, and the pin was a little undersized. It had a slight crater, but nothing like what I am seeing now. Thinking now, I should have lived with the slight cratering.
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Old 02-20-2007, 10:14 AM
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Re: Primer Reading

Unfortunately, you went in the wrong direction.

The oversized pin is so you can turn the pin down to fit the hole you have and get a close fit, NOT to enlarge you hole you have to fit the OVERSIZED pin.

The pressure on the pin (trying to push it back) is proportional to the area of the pin. 50,000 psi pushing against the area of the pin gives you the actual force... if you increase the area (larger pin) you increase the force, and now there is enough force to push it back, which is what you are discribing.

The solution is to have the bolt face bushed, and re-drilled for a 062 pin. Cost between 50 to 70 bucks.

.
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Old 02-20-2007, 10:36 AM
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Re: Primer Reading

[ QUOTE ]
Unfortunately, you went in the wrong direction.

The oversized pin is so you can turn the pin down to fit the hole you have and get a close fit, NOT to enlarge you hole you have to fit the OVERSIZED pin.

The pressure on the pin (trying to push it back) is proportional to the area of the pin. 50,000 psi pushing against the area of the pin gives you the actual force... if you increase the area (larger pin) you increase the force, and now there is enough force to push it back, which is what you are discribing.

The solution is to have the bolt face bushed, and re-drilled for a 062 pin. Cost between 50 to 70 bucks.

.

[/ QUOTE ]

Bingo...Gre-Tan rifles does a pile of these...50$

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  #6  
Old 02-20-2007, 10:38 AM
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Re: Primer Reading

TMR,

I would have to agree with Catshooter on this one. The problem with most modern center fire rifles is that they use a firing pin that is to damn large to begin with. Winchesters are terrible for this.

For a modern high pressure cartridge, a firing pin diameter of 55 to 60 thou is plenty large. Unfortunatly, most modern firing pins are more like 70 to 75 thou in diameter.

The larger the diameter of the firing pin, the more pressure is pushed back against the inside of the primer cup.

The larger the diameter of the firing pin hole, the easier it is for this high pressure to force the primer cup material back into the firing pin hole. Its a simple PSI over increased area issue.

If you have X PSI over a small area, the material supporting that pressure is more able to resist being forced back into that unsupported hole.

The larger diameter the unsupported area is, the more difficult it is for the primer pocket to resist this set back and you get primer cup flow into the firing pin hole.

This will happen in even very mild(for modern rifle) pressures. ANything much over 40,000 psi will do this.

If you are not having any problems with the function of the rifle I would not worry TO much about it.

Watch it as you develope your upper end loads and make sure you do not get near the point of piercing the primer. Also, if the receiver has been properly accurized you will not have much problem with this but if it has not and the firing pin is not hitting center on the primer, when you open the bolt, often times this little nipple on the primer will be sheared off into the firing pin hole which can cause several problems ranging from a firing pin wedging solid in the bolt and locking the rifle up to causing the primer to pierce on the next shot with the chips of primer material between the firing pin and the new primer.

Simply put, the problem is to large of a firing pin and firing pin hole.

If the problem causes real problems as the ones mentioned above, you can have the firing pin hole drilled out, and fit a threaded plug into the bolt face and then redrill the bolt face with a properly sized firing pin hole and refinish the bolt face. this is often not needed and the problem is seldom more then an annoyance but if it does cause problems it can be corrected. Also, the firing pin needs to be reduced to fit this smaller diameter bushing.

When you get your Nesika you will see what a properly sized firing pin will look like!!! [img]/ubbthreads/images/graemlins/grin.gif[/img]

Good Shooting!!

Kirby Allen(50)
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  #7  
Old 02-20-2007, 07:57 PM
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Re: Primer Reading

Thanks guys,

That is what I found out today......That is what I figured. Didn't even think about it when we did it. I was trying to cleanup Remington's sloppy job on the drilling.

Kirby....can't wait to see the Nesika [img]/ubbthreads/images/graemlins/grin.gif[/img]
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