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Primer Cratering Question

 
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  #1  
Old 05-30-2008, 05:31 PM
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Primer Cratering Question

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.
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Old 05-30-2008, 06:44 PM
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Well, it's pressure that causes cratering but there is a more common reason than excessive pressure. If the firing pin is undersized for it's hole that leaves an unsupported ring around the pin, as can a weak firing pin. If the primer cup is soft and/or thin, either can cause cratering even at fairly low pressures. If the rifle is new I'd suggest you contact the maker and explain your story, let them take a look at it if they will. Such cratering is not, of itself, sereious but it may lead to piercing and that WILL damage the bolt face.

It may be simplier to just change primers and see if you can find something with a harder or thicker cup that won't crater so easily. I once had to do that with a Weatherby Vanguard .243 but it stopped the craters.

Last edited by boomtube; 05-30-2008 at 06:50 PM.
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Old 05-30-2008, 06:50 PM
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i dont have personal experience with that caliber.but i do know that the velocities you are getting are a little slow for 180 grain bullets.and you said you are around 5 to 7 grains of powder shy of listed max.in most of my rifles,i can go past the listed max safely.but accuracy is not usually"up in the clouds".i have a mauser 98 that has been sporterized and rebarreled to 30-06.it craters with middle of the road loads.you should(i think)be able to get 3350 fps out of your rifle,so 3180 seems a tad slow.watch for heavy bolt lift,flat primers,circular shiny"smear" marks on case head. and high velocity.these along with primer cratering is what i watch for.i've found in my loading for distance shooting most loads seem to "shoot" 3-5 grains from max.jason
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Old 05-30-2008, 09:01 PM
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Thanks for the reply. Loaded up a round with a WLRM primer, same thing. I need the gun for Shawn Carlocks class next weekend, so I'll go ahead and do some more load developement and see what happens.

Thanks, Mike
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Old 05-31-2008, 08:04 AM
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Mike, I was reluctant to mention brands because things change but Federal primers fixed it for my Vanguard. Both CCI and Remingtons cratered.
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Old 05-31-2008, 09:12 AM
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Mike, boomtube hit the nail on the head, it's the clearance between firing pin and the hole in the bolt. i'd see if a smith has another firing pin that would be a little bigger and he could test the spring pressure while it's apart. i realize you have a new gun with warranty possibilities and a time table to meet. good luck with the different primers, that's probably your quickest and easiest course of action but a different firing pin is your solution to the problem.
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Old 05-31-2008, 06:25 PM
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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.

Is it really a problem, depends on how bad the cratering is. If its severe enough, you will get pierced primers. I would say from the velocities you are getting, the cratering is not caused by excessive pressure, I would say moreso from a problem with the firing pin and hole dimensions.

If your not seeing any shiny spot on the case head your fine with pressure. Remington factory loads will show a faint ejector ring on the fired case, very faint but you can see it with most of their factory loads, if you load your ammo to match that same faint ejector ring mark you will be very similiar in pressure.

ALso, if your bolt life is easy and your primer pockets are lasting you at least 4 firings your fine with pressure, more is better but 4 firings per case with a modern magnum is acceptable.

Simply put, in most cases its more of an eye sore then anything else but if its to the point that your getting the occasional pierced primer, something should be done to correct it.

Also remember that your shooting Solid bullets which are very hard compared to a lead core bullet and also I believe the E-tip is longer then say a 180 gr Accubond. If I remember correctly, they are nearly the same length as the 200 gr Accubond so they will have more baring surface then the conventional designed bullets which will limit your velocity a bit compared to a lead core bullet.

I would say your top end loads in the 3265 fps range may well be near the top end of what you will get with these bullets. The 180 gr Accubonds can usually be driven to well over 3300 fps but remember again, they have less baring surface and they are also a softer bullet which will conform to the bore dimensions with much less engraving pressure then a solid bullet design will.

Again, I would not say cratered primers is a high pressure indicator, when seen with other pressure signs, certainly it is but if its by itself, generally its a firing pin and hole dimension issue and unless it really bothers you, can just be left alone.
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