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Primer Cratering Question

 
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  #8  
Old 05-31-2008, 06:40 PM
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Join Date: Dec 2007
Location: bakersfield ca.
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Thanks to all for the information. I shot some more loads today and excessive pressure does not seem to show until around 3350 3375 fps with the E- tip. Best groups seemed to be 96.2 grns @ 3280. I'm going to fiddle with that seating depth a little tomorrow , then I'll load up 150 rounds for Shawns class next weekend.

Mike
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  #9  
Old 06-02-2008, 04:52 PM
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Join Date: Jul 2007
Location: HB New Zealand
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HI there, Ive had the same cratering problem as you have had with the exact same rifle, I also put it down to a firing pin issue, mine pin is a rather large 75 thou, whilst its annoying I dont really see it as dangerous unless they begin to pierce, Mine also had a rough plunger hole which chewed off little brass flakes as the bolt turned.
Good luck with yours and I hope it shoots better than mine is at the moment.
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  #10  
Old 06-07-2008, 09:59 AM
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Join Date: Mar 2008
Location: Alabama
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Quote:
Originally Posted by piutemike View Post
I shot my new Sendero SFll 300RUM for the first time today, breaking in the barrel and trying out some Nosler 180gr E Tips. Have to go unleaded this year in my area in Ca.

My starting load was 93 gr of retumbo Fed 215M primers and RP brass. Primers had small craters on everything from 93 to 95 grains. Nosler book lists Retumbo loads with 180 gr bullets from 95 to 99 grains so I didn't even come close to book max, keeping in mind Nosler told me to stay a couple grains under max. No other pressure signs, extractor marks, sticky bolt.

I'm pretty new to hand loading and have not encountered this with my other two guns I've loaded for. I used a chronograph, velocity was around 3180 to 3265 fps with the different powder charges.

My question is this, can something besides pressure cause primer cratering and how serious should this be taken? Thanks for your help.
You've gotten some good answers here. Primers vary in hardness. Cratering/flattening of primers is one of the least reliable methods for indicating excess pressures.

As for your loading, and "staying under max". I know you've read the books. You've read "never exceed max loads published". Etc, etc. Each gun is a law unto itself. Brass capacity differs brand to brand and can affect pressure. Primer "hotness" varies greatly brand to brand and can affect pressure. 95grs of Retumbo with a 180 bullet over a CCI Mag Rifle primer, wont be the same pressure as the same load over a Winchester Mag Rifle primer. You should own a chronograph to reload. It tells you much! It's a great tool IF you know how to apply the information it gives you to your loads and the data. I've seen handload that were, like yours, under book max, that were producing very high velocity, and obvious signs of pressure. However, the FIRST sign of pressure, assuming your loading techniques are sound, will almost always be velocity. If you're using proper powders for the application, you can almost always get the published velocity of most load whether it be 2 grains under the "book max" or 2 grains over. If you're running what the manual says is max velocity but you're 3 grains under the max powder charge...you can pretty well rest assured you've found YOUR GUN'S max. Don't think that because you're powder charge weights are under some arbitrary number in a manual that you're "under max".
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  #11  
Old 06-07-2008, 11:24 AM
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Join Date: Dec 2001
Location: Potters Hill, NC
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Quote:
Originally Posted by Fiftydriver View Post
It is more common in Win M70s and Savage rifles but bolts with a large diameter firing pin can also result in primer cratering even if the firing pin is a good fit to the firing pin hole in the bolt.

A modern firing pin should be roughly 62 thou in diameter and no more, unfortunately most are larger then this and many are MUCH larger then this, some in the 80 to 85 thou range, simply far to large to prevent primer cratering with modern high pressure chamberings.
Kirby,
Can the firing pin be taken out, reduced in diameter and put back in without doing anything to the bolt face hole? I can do this but don't want to compound the problem. Thanks, JohnnyK.
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