Question Regarding Primer Blanking….

[BillPa]

Great video, Bill. Thanks for sharing that. I get what he is saying about support behind the primer, and with higher than normal operating pressures, his fix is probably the best one.

As a follow up, while mess'n around in the shop the other day I had a brainstorm (brainfart?) and thought how hard can it be so I made this...
http://oi66.tinypic.com/jrtdox.jpg

Looking at a few primer dimension charts the largest cup diameter was .2120" so faced a chunk of bar off square then pre-drilled it with a #2 bit and finished it to .250" x .300" deep with a .250" end mill bit. I made the bushing using the shank of a G8 bolt to .252" OD"x .330" long for a interference proud press in fit. After pressing the bushing in I drilled the pin hole to .062"(1/16") and faced it flush.

Thoughts?

Bill

[Texas10]

That's perfect, Bill :thumb:

If I had a Mill, I'd be doing what you did instead of sending it back to the factory:cool:

Ream to fit after pressing the insert in or let the press fit shrink the hole to a close fit. Either way, fixes the issue perfectly in my book.

What's optimal, half thou clearance? Full thou?

[Texas10]

Just to catch y'all up on what's going on with this new model 12fv blanking primers issue. Factory has had it about 10 days when I called earlier this week, and nothing had been done, and they'd never linked up the online service request with the gun, so it was sitting at "the range" for test firing ( I had enclosed as-fired brass from factory loads that exhibited blanked primers).

Service tech stated that they were weeks behind on the email system, and she was "closing the tag" on this issue.

I asked her to please copy my email to the techs so they might have some idea where to start. I should have included that with the gun, but neglected that little detail.:frusty:

BTW I see the 100 dollar rebate is on again for ANY model 12. Woo-Hoo! Cabelas here I come!

[kkeene]

Stay away from cci 400 primers and use cci 450 or cci br instead. Your problem will most likely go away. 400 primers have very thin cups. Primer cup hardness is also a factor.

http://www.jamescalhoon.com/primers_and_pressure.php

[Texas10]

Big brown truck arriving today, unfortunately Savage failed to do anything to fix the blanking problem. The reason? They never connected the email chain to the gun and were clueless as to what the problem was. Even though I enclosed spent brass with blanked primers. They shot it and boxed it up without ever trying to contact me or look into the CS database. My subsequent phone call was apparently an hour too late to link my service request to the gun.

The gal in CS apologized and is sending me a firing pin, no charge. I am faxing them a waiver incase I need to order additional firing pins until I get one that fits properly.

She did go to the "gunsmith" to ask about changing the firing pin to one that fits better. The answer was "you can't change the size of the firing pin". I said that I don't want a custom made firing pin, I just want one that is made to the nominal print dimension, and not one that is out of spec.

Am I being stupid? This seems like it should be a really simple process, yet it failed miserably.

Maybe next time I'll enclose a burner phone and have the GS call me directly. :beaten:

[Texas10]

Gun arrived today, bolt was in the fired condition and wouldn't install. Probably triggered in shipment.

Anyway, unscrewed the BAS and reset the fireing pin. Going to wait until new firing pin arrives and see if it fits the bolt head better.

[kkeene]

You don't need to disassemble the bolt to reset the firing pin. Just catch the button on the edge of a bench and push the bolt down.

[Texas10]

New firing pin arrived yesterday. Measured .002 larger in diameter than original, so installed and set protrusion to .033".

Loaded some rounds to same receipe that exhibited the problem with blanking, and shot them today.

Problem solved. Only showed some partial blanking at max load, no full blanking (pierced primers).

Thanks for all your good advise, guys. Really appreciate your experience and knowledge and willingness to share.

[Texas10]

Today I ordered 6 new firing pins, hoping to get one that fits with less than .002 clearance. Asked the Customer Service rep if he had the drawing available to see what the tolerance was on the pin dia, but he had no idea what to look for and couldn't share with me the details if he could find it.

Does anyone here know what the min-max diameter is for the magnum pin? Bolt head has a .073 hole and I'm hoping for something in the .070 to .072 range. I can always reduce a too large dia pin. Adding metal is a bit more problematic.

[sharpshooter]

Ordering 6, hoping to get one the right size is probably nothing more than a crap shoot. The hole size on the bolt head has a range from.072" to .075". The firing pin tip is .068" to .071". That's what the print says anyway, but that doesn't mean that they stick to it.

[Texas10]

Thanks, sharpshooter. I was hoping someone had knowledge of the drawing and would be willing to share that. This says a lot about the probability of getting a good shooting Savage, vs one that is problematic like this new 12 FV was.

Based on your numbers, there are 16 possible combinations when it comes to tolerance stack and fit of pin to head. And if pins are not hand fit to the bolt for clearance at the factory during assembly of the bolt, and randomness applies, then fully half in each group of 16 rifles will probably have problems with primer blanking because of excessive pin to bolt head clearance.

One out of 16 will have .001 clearance, and one will have .007. But 8 will have .0035 or more clearance, the amount that this rifle begins to experience partial blanking (cratering) when at or near max pressures.

Might explain why their warranty repair shop is apparently so busy.

[sharpshooter]

Cratering is not always caused by excessive clearance around the pin. Most of the time it can be cured by re-profiling the pin tip.