Every since I started reloading, folks have been telling me that flattened primers are an indicator of excessive pressure. I honestly dont believe it anymore. I usually load to the max reccomendation for hunting but I did reload some to the starting specifications for 3 rifles and they all still have flattened primers. Doesnt it stand to reason that as brass gets reloaded that the primer pocket just gets worn down, hence any old reload will puch it back out? Were talking about minimum pressures of 40,000 psi here. It seems to me shadetree engineering at best to stick solidly to this theory. What do you think?
Flattened primers can mean excessive pressure but it can also be caused by poor head spacing or loads that are to light and detonate instead of burning the powder. Primers backing out can be loose primer pockets or again, excess pressure. You are right to assume that it does not automatically mean high pressure. However most of the cases Of flattened primers I have had have been excess pressure.
Another consideration could be what brand of primer are you using. I have found the cup metal on Winchester and Remington primers to be somewhat stiff while the cup metal on Federal's to be somewhat softer. Alson don't forget the warmer the weather the higher pressures you'll see, hence a load that is safe in the spring and fall may produce higher pressures in the summer.
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Flattened primers can mean excessive pressure but it can also be caused by poor head spacing or loads that are to light and detonate instead of burning the powder. Primers backing out can be loose primer pockets or again, excess pressure. You are right to assume that it does not automatically mean high pressure. However most of the cases Of flattened primers I have had have been excess pressure.
As a general rule, flattened primers are NOT a reliable indication of EXCESSIVE pressures - the causes of flattened primers are many and varied! RELIABLE indicators of excessive pressures include bolt face/ejector slot marks on the case head, difficult bolt opening, and primer pockets that expand to the extent that it becomes easy to seat new primers (OR WORSE). Primer pockets don't WEAR bigger just from the friction of punching out and installing new primers. They expand due to too-high pressures!
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You ought to do what I did. I went on a quest when starting reloading to see what the indicators look like. so I loaded up some shells past max in .2gr increments. What I found, is flat primers are a great indicator. Cause if your not sure your overpressure over flattened primers, you probably are not over pressure yet. I saw withing 1.5gr over max primers that looked like it was part of the brass head it was so flat, and bolt lift started to get tough.Now thats a flattened primer. I found on one case not only flat, but pierced primer. I decided not to go further and find out how much it takes to lock the brass up in the gun.
I would find out about that 2 or so years later when taking a partition load, and trying to put it to a trophy bonded bullet. Not only flat primer, but had to take a cleaning rod and knock out the brass gently.
Federal is always going to look flat, and winchester and CCI will give you good indicators. But when your well over max, you won't have to scratch your head, you will know a definate yes.
BigCountry nailed that one. A FLATTENED primer is one that looks like it is part of the brass. There is little or no line (ring) around it.Most will flatten some on the boltface, but they don't take out the ring unless there is a pressure issue. It is usually found together with a hard to open bolt.
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ballistitition from sierra told me that flattened primers alone don't mean much, if its accompanied by another sign then you need to address it.
Also alot depends on case design, I don't get ejector pin marks on my sharp shouldered, little body tapered wildcat rounds, all I get is loose primer pockets.
case head expansion is the one sign that definately will tell you if your over pressure.
RR
A flattened primer aloneis not, in itself, an indication of high pressure. A flattened primer along with a hard to lift bolt, loosened primer, a shiny case head where thebrass flowed into the ejector hole,or brass that has flowed into the extractor groove are definite indicators of high pressure. In two of my .30-06s, i get away with using a load of 3031thatistwo tofour grains above anyones printed maximum load for a 150 grain bullet: But this can only be accomplished with the use of Winchester cases.
flattened primers
