WOW! You all really liked the "what is high pressure" post. To me, that means a BIG MARKET.

How much would you pay for primers certified to duplicate the ignition characteristics of different manufacturers products that would also tell you the PSI of your load after firing?

There are a number of ways to accomplish this, and it is at least as good as the copper crusher approach.

Sabot, what did you have in mind?

I think I'd pay $20 for 100 primers if they could somehow tell me the peak pressure with decent accuracy. I expect fans of PRE/CHE will chime in and say it's a waste of time/money.

Well, I have already established a very strong relationship between primer diameter and velocity in several rifles which have good headspace. As you know, too much headspace can allow the primer to protrude on ignition and then be overly flattened by the case as it expands to full pressure aganinst the bolt face.

The other factor is the slope or radius of the entry to the primer pocket...this varies by manufacturer and caliber. More room to expand results in more expansion for a given level of pressure.

With that said, I have data for the WLR primers in remington cases for several different calibers in different rifles and the R-squared for primer diameter vs velocity is .9695 or better. My guess from comparing these velocities to reloading manuals is that these rifles get to 55,000 psi with the primers staying at .210 and are at or near 65000 psi when they reach .217.

This can be improved by making the primers out of metal with more uniform crush characteristics, and using seating techniques that carefully measure seating depth and seating pressure.

quote:

How much would you pay for primers certified to duplicate the ignition characteristics of different manufacturers products that would also tell you the PSI of your load after firing?

If there was a reliable method of determining pressure this is a big thing to me.....

Who knows.....I might be willing to shell out a buck each for them!!!

I like your idea about correlating primer pocket seating pressure with maximum PSI. Possibly such an instrument could be devised. But, it would need to be calibrated with data from a state-of-the-art ballistics lab like that used by IMR/Hodgdon.

I know some of these big-time labs use brandnew brass for each firing, for which they'll have PSI. After one firing they throw away the brass - maybe they would give you the spent case. Sabot, you could correlate seating pressure with the recorded maximum PSI to which the brass had been exposed. You would need to design an instument to accurately measure seating pressure.

If one could get pressure readings as reliable as CUP with a special primer, I'd pay a dollar or two for each primer.

There is NO question that at a dollar per primer, this can be accomplished and there will be no problem getting investment money or grants from DOD to do this. Heck, at a buck each, you are talking a 33 fold increase in price. The flash hole simply becomes a sealed vent hole of known diameter, so the force on the primer cup walls can be accurately measured by the amount that the external wall flows into the seating radius leading into the primer pocket.

As primers "flatten" they get a mushroom shape due to this flow. The diameter of the mushroom head will give a good indication of pressure as long as the cup is carefully formed from a metal that crushes uniformly. Even the current steel cups work fairly well, but this can be improved by going to a different alloy.

I would like to get more insights and opinions on this potential...could someone move this topic so it will start over in "Reloading" and call it something flashy, like "cheap pressure indicator" or something like that?

Why not measure case head expansion instead?

Sounds alot like the copper crusher system. I`ve been told they need a "tareage" (table for lack of a better word) to help with converting the crush to a psi figure. The CUP system uses these tables as the copper pellets not only have minute hardness variations which means the crush changes with each lot, but also behave differently at different ranges of pressure. IE; .002" crush in your 257 Rob @45000CUP doesn`t indicate the same pressure value as in your 270 Win @ 52000 CUP.
The chambers headspace and case primer pocket will also change the expansion and will need to be standardized to give any guarentee the expansion is consistant with the pressure on it. Then there`s the fact no two people measure the same with out some practice, especially when looking at measurments finer then .001" where you`ll likely have be to get anything useful from them.
I`m not saying it won`t work, I just think there`s more to it then finding a metal alloy that reacts consistantly.

You guys have allowed yourselves to be drawn into theoretical lunicy on pressure signs. Look at the "face" of the case the part with the numbers and letters, if there is "ANY" brass flow into the ejector hole or slot your load is hot. Any shiny spot period. This will surely happen before a Magnum primer shows much pressure and about the same time a standard primer shows much flattening.

Primer diameter would be measured by simply dropping it down a graduated clear tube with a gradual taper so it stops when it decends to its largest diameter. The diameter and pressure could be read from graduations in the side.

Primers will grow a lot more than the case head, so its easier and more accurate to use the primers.

But you are all assuming that every primer cup is made of exactly the same alloy with the same hardness, and the same amount of priming mix. You are all further assuming that the chamber is so tight that the firing pin will strike the primer in the exact same spot every time. There are just too many variables.

Also, take this into account:

36 grains of H380 will completely flatten the primer in my 22-250 load if the powder is resting against it during ignition.

If the powder rests afgainst the base of the bullet instead, the primer shows absolutely no signs of flattening. In fact, it looks like the round never fired, but for the firing pin indentation.

By all accounts one would think that there is probably a 30KPSI disparity between the two powder positions, but we all know its more like 5KPSI.

The bottom line is that primer appearance, or the diameter of the 'mushroom' is not a reliable way to gauge pressure.

quote:

Originally posted by Sabot:
Primer diameter would be measured by simply dropping it down a graduated clear tube with a gradual taper so it stops when it decends to its largest diameter. The diameter and pressure could be read from graduations in the side.

Primers will grow a lot more than the case head, so its easier and more accurate to use the primers.

Hey Sabot, Your "original idea" does seem to have some interesting possibilities to it. The method you describe above to measure the expansion shows you have put some excellent thought into it. That measurement method is so simple, even the Strain Gauge Worshipers could "probably" figure it out in a week or two.

I also agree that getting Pressure Indications from something which gets the actual Pressure "First Hand" rather than "Second Hand"(like the Strain Gauges) is always the best way to go.

As some above have pointed out, there will be some problems and stumbling blocks to get past if you choose to pursue the idea, but that is true for anything worthwhile. You might want to "Patent the Concept" to protect your idea.

I wish you the very best of luck in your efforts.