Pressure measuring primers?

[DRNewcomb]

I was thinking about the subject of "reading the tea leaves" for signs of excess pressure, when it sort of struck me: Why couldn't a primer be designed that would record peak pressure with some degree of reliability? I began thinking about it and came up with an idea, that I'd like to run by the group.

Stamp the primer cup of metal that is thinner near the center and thicker at the edge. Form the cup with a very rounded shape, perhaps with tiny concentric circles etched around the center. The rest would be of conventional Boxer design. You might need to use a special priming ram with a concave tip to seat the primer to prevent crushing.

When the round is fired, the primer is crushed against the bolt face as with any other primer. However, the degree of crushing is predictable. Say that for a rifle, the concentric rings are graduated in 5K PSI increments starting at 35K PSI and going to 60 or 65K PSI. You examine the fired primer with a jeweler's loop counting the rings out to the edge of the flatening. This would read the peak pressure.

I don't know about anyone else but if it worked, I'd be willing to pay $1 each for primers like this. I Googled this topic and didn't see anything like this. Has anyone seen this this idea before? Is there a reason why this is a stupid idea?

I understand that there are strain gages that you can glue over your rifle's chamber and read the expansion of the barrel at the chamber and get real nice graphs of pressure vs time, etc. but these have some disadvantages:
1) You have to glue the gage to the barrel.
2) It measures strain, not pressure, which must be inferred from firing test cartridges.
3) Each gun needs its own glued-on strain gage and calibration.

 

[John Russell]

I was thinking about the subject of "reading the tea leaves" for signs of excess pressure, when it sort of struck me: Why couldn't a primer be designed that would record peak pressure with some degree of reliability? I began thinking about it and came up with an idea, that I'd like to run by the group.

Stamp the primer cup of metal that is thinner near the center and thicker at the edge. Form the cup with a very rounded shape, perhaps with tiny concentric circles etched around the center. The rest would be of conventional Boxer design. You might need to use a special priming ram with a concave tip to seat the primer to prevent crushing.

When the round is fired, the primer is crushed against the bolt face as with any other primer. However, the degree of crushing is predictable. Say that for a rifle, the concentric rings are graduated in 5K PSI increments starting at 35K PSI and going to 60 or 65K PSI. You examine the fired primer with a jeweler's loop counting the rings out to the edge of the flatening. This would read the peak pressure.

I don't know about anyone else but if it worked, I'd be willing to pay $1 each for primers like this. I Googled this topic and didn't see anything like this. Has anyone seen this this idea before? Is there a reason why this is a stupid idea?

I understand that there are strain gages that you can glue over your rifle's chamber and read the expansion of the barrel at the chamber and get real nice graphs of pressure vs time, etc. but these have some disadvantages:
1) You have to glue the gage to the barrel.
2) It measures strain, not pressure, which must be inferred from firing test cartridges.
3) Each gun needs its own glued-on strain gage and calibration.

You wanna pay 4x to 10x the current prices for primers??? There is no way in hell that primer companies are going to take on that risk/responsibility/liability... they already have enough problems just getting the same ol' boring primers out to us.

Also, the actual pressure (in numbers) is not important, it is how your rifle reacts to pressure - some rifles and brass can take a lot of pressure without blinking and take it is stride, others show signs, (and problems) at much lower pressures.

There is no easy way out of it - you need to learn how to read pressures in firearms.

 

[DRNewcomb]

You wanna pay 4x to 10x the current prices for primers???

NO. These primers would be used only for testing new loads. Yes, I understand that primers make a difference in pressure but the idea would be that such primers would function like the standard regular or magnum primers as far as the powder was concerned.

 

[John Russell]

NO. These primers would be used only for testing new loads. Yes, I understand that primers make a difference in pressure but the idea would be that such primers would function like the standard regular or magnum primers as far as the powder was concerned.

That just raised the price 10 more times - I can guarantee that the primer companies will NOT get involved with this idea. You are missing the point - who cares what the pressure is if things are working great, and what difference does it make if your super primer says 50,000 PSI, and you have hard bolt lift, and ejector stamping and wiping??

There are many shooters that are using 70,000 psi loads, and others that are running 45,000 psi loads. There is NO standard for reloading, just guide lines for new manufactured ammunition .

 

[Sniper338]

I gotta agree with the other guys... 30k 45k 50k 100k psi.. i dont matter what the number is. Its what your rifle does that matters.

And primers already tell you if there is pressure issues. Attention to detail is all it is..

 

[fguffey]

I was thinking about the subject of "reading the tea leaves" for signs of excess pressure, when it sort of struck me: Why couldn't a primer be designed that would record peak pressure with some degree of reliability?

Many years ago I had an epiphany, I thought, wouldn't it be nice if there was something in the chamber when the trigger was pulled and then I thought; there is, the case is in the chamber. That was before the Internet, in the old days case heads upset and increased in diameter and in got shorter from the cup above the web to the case head.. The primer pockets increased in diameter and the flash hole increased in diameter. And then there was that thing with the shoulder of the case and shoulder of the chamber.

F. Guffey

 

[DRNewcomb]

Many years ago I had an epiphany, I thought, wouldn't it be nice if there was something in the chamber when the trigger was pulled and then I thought; there is, the case is in the chamber. That was before the Internet, in the old days case heads upset and increased in diameter and in got shorter from the cup above the web to the case head.. The primer pockets increased in diameter and the flash hole increased in diameter. And then there was that thing with the shoulder of the case and shoulder of the chamber.

F. Guffey

Yeah. But none of those things are calibrated in any way or repeatable. Now, a very thin crush gage would be.

 

[RonAKA]

I think you have a good basic idea. The primer would have to be manufactured so you still got reliable ignition, and the firing pin did not pierce the cup. The possible technical issue I could see is that the standard primer does not even come close to holding the pressure of a normal load. It depends on the bolt face for strength. So I am not sure you could design a cup that would be soft enough to fire, but strong enough not to fully deform to the bolt face. The other commercial issue would likely be the cost and low quantities, that might make the production cost not practical.

The relationship between stress and strain is very well known. The strain gauge approach is going to be very accurate, but certainly not cheap.

 

[KMart]

The pressure recorded with the test primer would only be good with the test primer.
Change the primer to brand x,y or z, and all bets are off on what the pressure would be.
You would have to always use the test primer.

 

[Webster]

The pressure recorded with the test primer would only be good with the test primer.
Change the primer to brand x,y or z, and all bets are off on what the pressure would be.
You would have to always use the test primer.

No reasonable, not needed. Even if they worked and were a decent price you would have to sign a liability release.

 

[GrocMax]

Hrmm......plasti-gage for metallic cartridge case pressure measurement.

That's all CUP is anyways.

 

[JohnKielly]

... and would they be consistent irrespective if the status of the case? It's recognized that cases too short for a snug chamber fit can show signs not inconsistent with pressure signs (I've seen both brass extrusion & totally flattened primers an an extreme case with an old military shooter). Again, what would happen if the primer pockets were less than snug?