Flat primer?

[Big Mc]

Shot 9 rounds and noticed one primer flatter than others? All components being equal and all powder hand weight? Rounds were on the light /mild side ,barrel not hot and cool day. Round was not last out of barrel . Barrel and chamber clean. The primer was flat enough to call it a pressure spike for sure

I also mark odd cases whit a sharpie . and if is different the second time TRASH it.. Just my two cents.. Tommy Mc

 

[243winxb]

.001 tension

Light neck tension may let the bullet move to soon, causing a pressure spike.

Mostly happens with slow burn rate powders, lots of free bore, light for caliber bullets. Mostly large case magnums.

 

[Bart B.]

Light neck tension may let the bullet move to soon, causing a pressure spike

I've shot thousands of rounds with light bullet release force (bullets easily pulled out with fingers) and any pressure spike there was didn't change fired primer shape compared to same ammo with bullets needing 30 pounds of force to pull the bullet out of the case.

What's the minimum bullet release force in pounds wherein any less from not enough case neck grip on bullets will cause that spike?

How many microseconds is too soon?

What's the estimated pressure at such spikes and how many microseconds from primer detonations do they happen?

 

[jepp2]

Shot 9 rounds and noticed one primer flatter than others?

After much discussion about "flat primer" and what caused it. Let's start by trying to understand how flat. In the pic below (handgun, I know) you see 3 primers. Left is normal for a very light load, center is flatter but normal for the load, right is flat due to higher pressure than desired. So I am guessing yours looks like the center primer, right?

During load development, I will on occasion see a primer like the middle one, when the rest are like the left one (or somewhere between the left and middle one). And I weigh all my charges and don't push it on hot loads. And yes, all my cases are sized the same, etc. Can't explain it, don't try to. And it isn't always with the highest charge I am testing.

 

[muleman69]

After much discussion about "flat primer" and what caused it. Let's start by trying to understand how flat. In the pic below (handgun, I know) you see 3 primers. Left is normal for a very light load, center is flatter but normal for the load, right is flat due to higher pressure than desired. So I am guessing yours looks like the center primer, right?

During load development, I will on occasion see a primer like the middle one, when the rest are like the left one (or somewhere between the left and middle one). And I weigh all my charges and don't push it on hot loads. And yes, all my cases are sized the same, etc. Can't explain it, don't try to. And it isn't always with the highest charge I am testing.

View attachment 1037878

Yes you are spot on, mine look the same. Great post TKS

 

[searcher]

Question was asked as to how much a shoulder would have to be "over-bumped" to cause a flat primer. Has been a long time since I ran into that - but have run ammo where the die was not set up properly and those primers can get pretty darn flat. I would think .010" would not usually be a problem to cause it - but I don't think you would have to go much more to see some form of it. Say one of those cases went .005" over the rest - that might very well do it. I have a Ruger ultra-light rifle in .257 Roberts with a factory barrel. Every factory load tried (and reloads with never-fired factory brass) will flatten the primers to the point it looks like serious over-pressure. After blowing the shoulders forward by seating the bullets into the lands, the "lengthened" cartridges no longer show any signs of this problem after bumping the shoulders back .003". I do recall measuring the base-to-shoulder length of unfired brass and comparing to brass which had been blown out. I can't recall for sure, but I believe it was around .015". As you might imagine, even having .010" space creates quite a variation in firing pin initial strike.