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Flattened Primer Question for 300 RUM

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Unread 01-21-2013, 11:58 PM
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Join Date: Aug 2006
Location: Longmont, CO
Posts: 188
Re: Flattened Primer Question for 300 RUM

I've used Federal primers exclusively for years and have always found them to flatten more than CCI or REM running at similar pressures. They appear to be softer, requiring less pressure to flatten them than the others.

How well your primer pockets hold up is a better indicator as to your pressures than a flattened FED primer based on my experience.

I now use Quickload to check my pressures in conjunction with my chronographed velocities.

Just my 2 cents.

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Unread 01-22-2013, 12:01 AM
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Join Date: May 2008
Location: South of Canada and North of Wyoming
Posts: 6,068
Re: Flattened Primer Question for 300 RUM

I also use Fed primers
- Mark

You will never know how much it has cost my generation to preserve your freedom. I hope you make good use of it.
~ John Quincy Adams
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Unread 01-22-2013, 01:08 AM
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Join Date: Jan 2013
Posts: 1
Re: Flattened Primer Question for 300 RUM

Originally Posted by ProfessorM View Post
Hunting season has ended and shooting season has begun where I am at! I have a 300 RUM Sendero, stock 26 inch barrel that is capable of sub moa out to 1000 yards if I do my part. My load is 92 grains of Retumbo, 215 Bergers, Rem brass, Fed 215 match primers, 3.690 col (can fit one in magazine), and it chronos at 3100 fps. Velocity seems to be in line with what most folks are posting. (I know, everything on the internet is true) The only pressure signs I'm getting are flattened primers. No sticky bolt lift all. My question is this....Should I back off until primers quit flattening or keep this load? What would you do? It's scary accurate and I'm somewhat hesitant to change. I have 48 pieces of 2x fired brass tumbling right now. Going to give the gun a good a cleaning, shoot my final two rounds as foulers and either duplicate the load posted above or change it up a little as time allows.
On the surface with the information provided the load (charge weight) does not seem excessive but as you know this can mean little depending on other factors, especially when working in the upper spectrum of the load range.
(I have many rifles that reach their maximums before most published data maximums would indicate.)

“Flattening primer appearance” can mean many different things to many different people
It really comes into play when you “know” your rifle.
Like, is there still some exposed radius (curve) to the edge of the primer face?
Or is it completely flattened to the point this is completely eliminated or even has flowed over the case head.

You did not list your starting charge weight on the “work up”
Since we know you used a proper work up routine it would have been more productive to monitor the primer condition and make notes on the way up as charge weights were increased every tenth or two tenths.
This would be preferred over doing it in reverse (backing down) because the cases will have more cycles on them and this alone can skew the “readings”

You list a COL of 3.690”
This while on the long side (SAAMI MAX COL is 3.600”) this may or may not contribute to the condition but do you know the distance from the Berger’s ogive contact point to the lands when chambered?
This would be helpful to know so it could be placed in the evaluation.

You didn’t mention how you size these
Did you FL resize the cases or neck size only on fire-formed cases?
This can make huge difference in primer appearance
If you FL resized the cases there will be several thousandths added to the "actual headspace" tolerance when the cartridge is chambered.

What can happen here is, when the firing pin strikes the primer the cartridge is driven forward until the shoulder contacts the chamber, on ignitions the cartridge is slammed back onto the bolt face, while the cartridge under ignition was expanding during the pressure generation cycle the primer may be forced rearward several thousandths before it can be stopped by the bolt face
Since the pressure is now equalized in the chamber the primer will not get “reseated” it will flatten.
Obviously this is all taking place in milliseconds but the dimensions do change under this scenario
You usually don’t see this condition on fire-formed cases because the case has been pressure formed to the chamber so the case cannot be moved forward by the energy of the firing pin.
(One of the reasons we fire-form the cases)

While you may be safe, if it were me I would want to know why the primers were flattening
Because if it is from something improper or a high pressure issue the current load configuration could come back to haunt you.
While currently not problematic, it could be something as simple as you using this load on a hot day and the high temps combined with the “problem” (whatever it is) send the spike over the limit of the case and or primer and you may have more than a stuck bolt to deal with.

Good Luck
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