need a simple pressure guage

[nekshot]

It would be neat if someone made a softish thin donut shaped piece of tape that could be placed on the back of the cartridge before loading. It would have to be sticky on the one side and have a hole in it for firing pin to go thru and after you shoot the pressure would smash it according to the given load in cartridge. You would eject the empty case and measure the amount of smash and compare it to the printed data supplied with the kit of tape/donut shaped tape which would have 20,000 psi, 30,000 psi, 40,000 and 50,000 and even 60,000 for those with hair on your chests. Inventers have a go at it and I will be your first customer!

[oneokie]

The problem with something like that in a gun with a rotating bolt is that the turning of the bolt into battery would smear the compound.

[RED333]

http://www.fujifilm.com/products/prescale/prescalefilm/
http://www.tekscan.com/pressure-indicating-film.html
http://www.sensorprod.com/index.php

Just a few I found looking for "pressure recording film".

[Garyshome]

Interesting idea! If it worked it would answer quite a few questions.

[texassako]

Wouldn't that measure bolt thrust and not pressure?

[Cowboy_Dan]

Or what if they made it like the pressure stickers on Mythbusters where if the pressure excedes a certain level it trips an indicator. Would be helpful for load devolopment.

[Blacksmith]

What the head of the cartridge sees is not an accurate measure of the pressure in the chamber. What you describe would measure the force the cartridge head exerts on the bolt face but that is dependent on a number of factors in addition to the chamber pressure for example the thickness of the brass, the hardness of the brass, the size of the chamber reamer, the finish of the chamber walls, the amount of lubricant on the case and chamber, etc. All these and some other factors effect how much and how fast the case moves when the cartridge is fired. Chamber pressures are measured in special test barrels that allow direct gas impingement on either a piezoelectric transducer or copper plug for measuring pressure although the two systems do not give the same results. You might be able to mount a strain gauge on the chamber area of the barrel and get readings that could be approximately correlated to pressure readings but it wouldn't be cheap.

[JSnover]

If the film was very thin you might be able to stick on the side of the case. But a tight chamber might skew the results.

[Echo]

And - how thin are we talking, and how accurately would we be able to measure the thickness post-firing? Probably have to get down to tenths, at least...

[nekshot]

I was kinda thinking like plasta gauge for measuring crank/rods.

[Larry Gibson]

"You might be able to mount a strain gauge on the chamber area of the barrel and get readings that could be approximately correlated to pressure readings but it wouldn't be cheap."

Not only "might" but it's been done for quite some time. The Oehler M83 is the industry standard for doing just this to measure pressures in actual firearms and test barrels. I use the Oehler M43 (the M83's smaller brother) Personal Ballistics System. No it is not "cheap". The cost of the M43, the laptop computer and assorted equipment is expensive. The strain gauges must also be permanently affixed to the barrel (something you may not want to do) and for proper correlation of readings the gauges must be placed over the middle of the cartridge. That is not possible with some cartridges in some actions. The cost, the time to enter correct data for a test, the time to set up and take down the equipment and the systems check are not something for the casual reloader. There is additional cost for "reference" ammunition (actual or factory) and a test rifle with a large lot of ammunition for a "systems" check before use at each set up. Doing all this can give excellent and consistent measurements (the M43 PBL measures numerous internal and external factors of ballistic performance).

In the picture you can get an idea of the "bursting radius" I have at the range with the M43 set up for testing. It takes me approximately 45 - 60 minutes to set up without the "hey whatcha doin" interruptions before actual testing can be undertaken.

Larry Gibson

117498117499

[RED333]

Larry do you need a helper, I just might work for free just to learn.LOL