I occassionally get one or two flatten primers out of 15 or 20 rounds of the same load. Is this a sign of a weakened primer pocket?

Usually flattened primers indicate a load generating a higher than "normal" pressure.

I agree that normally it would be a high pressure indication but all other rounds look perfect with no signs of a pressure problem on the two that I found there was no other indication other than slightly flattened primers. The brass is aging and that is why I suspected a weak primer pocket.
Thanks

how did the primers feel when you seated them? If they felt a bit too easy, they are probably loose.

How many firings on the brass? max loads? Chrono readings a bit high?

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Originally posted by Dwight:
Is this a sign of a weakened primer pocket?

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I don't think so, I've been using some very loose primerd loads to see what happens.
The way some of my friends reload, it sounds
more like a bit extra powder getting in. After
a powder measure hangs a bit up, for instance.
Also a fella here called StonyCreek I think, was
telling me if these cases were FLSized (a bit too much), the primers would LOOK more flattened
than say some N/sized loads.
John L.

quote:

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Also a fella here called StonyCreek I think, was
telling me if these cases were FLSized (a bit too much), the primers would LOOK more flattened
than say some N/sized loads.
John L.

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Yep, that's what StonyCreek said. Primer flattening is often a result of longer-than-necessary headspace (which may have several causes, including excessive sizing). If some of the cases got more sizing than others (or were previously unfired, for example), then they could show more pronounced primer flattening than the other rounds, but still be producing similar pressures.

This is NOT to say that your gun has "excessive headspace", just that some of your rounds may be a bit shorter in the base-to-shoulder dimension than others. A short case allows the case to be pushed forward upon firing, then the primer backs out just a tad from the internal pressure, then the case stretches backward against the bolt face flattening the slightly protruding primer.

Another cause could be mixing different brands of primers (unlikely, however). Various brands have cups that are harder or softer (or thicker or thinner) than others. The thin or soft cups naturally flatten more easily than the hard or thick cups.

Rounds heated in a hot/warm chamber before firing.

Thanks guys. I dont' know the number of loadings but quite a few and I have had a few primers that seated too easy and I have tossed them in the trash. I could have just let a couple get by. I weigh every load and never used a powder measure. A little slow but I don't shoot enough to have to hurry my loading.

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Originally posted by Dwight:
A little slow but I don't shoot enough to have to hurry my loading.

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Seeing as you new here I won't scare you on how
many ways I've discovered to get the wrong load in a case when using scales.
I need to check everything, and check often.

I don't believe that a "loose" primer pocket will cause a "flat" primer. The primer will move back against the bolt face even with light loads. My bet would be on short cases. Brass with loose primer pockets should be scraped because it is getting tired.
Good luck1