Measuring Cartridge Pressure

[justindad]

What do you do about measuring cartridge pressure?
*
I found RSI Pressure Trace II, but that is overkill for what I want. I just want to know peak pressures for boolits that have no load data.

[Larry Gibson]

QL (Quick Load) can give you an estimate of the pressure. If you use QL just remember that "garbage in, garbage out", i.e. you must enter as much correct data as possible. Then you must understand the QL answer will still only be a questimate.

I've been measuring pressures of numerous cartridges for 15 years now using an Oehler M43 (no longer available) and am also using a Pressure Trace II system. Other than with such systems or a much more expensive systems, there is no way to measure the actual pressure of cartridges.

[racepres]

Allow me to throw a wrench in yer Monkey works
Nope... changed my mind... I was about to suggest Primer appearance and my Method... But... Nope... Not a good Idea..

[MarkP]

It would very expensive to get set up to measure absolute pressure.

Pressure bbl with transducer with SAAMI min chamber.
Universal receiver (to hold psi bbl)
Temperature and humidity controlled room to test in.
Calibrated brass (to input slope and offset) or your own brass calibration system. Small bbl with chamber and transducer is pumped with hyd oil to prescribed levels and transducer output is recorded and plotted against hyd Pressure to develope a curve for each lot of brass.
DAQ system
Reference ammunition to calibrate your bbl. (Probably not available to non SAAMI members)
Could use strain gauges on a rifle to compare with factory ammo. But that method would have the assumption ammo is loaded at or near SAAMI MAP and would not give you an absolute value just a comparison.

CUP method would be less expensive and does not require calibration for the brass cartridge. This will not catch peaks like piezoelectric transducers.

[Hick]

Not clear from your post what the issue is, but Just because there is not load data for a particular bullet does not mean there is a problem. Similar bullet, slightly heavier and similar bullet, similar case capacity can be used to find a safe starting point.

[Reg]

Could a water measurement of the case be used in some way as a comparison ?

Say bore dia. being equal and case shape being approximate ?

[dtknowles]

What do you do about measuring cartridge pressure?
*
I found RSI Pressure Trace II, but that is overkill for what I want. I just want to know peak pressures for boolits that have no load data.

Without expensive equipment the best you can do is measure velocity and compare to the most similar cartridge/load/bullet/powder for which you can find pressure data. For instance, I load cast bullets in a 30 BR long, I compare my velocity to 30-30 and 300 savage pressure data or max load data with the same powder and similar or the same bullets.

[olafhardt]

I am a retired engineer who had worked with calibrated equipment a lot. It is my opinion that there is no way to properly calibrate high pressure measuring equipment as there is no primary high pressure standard. The methods we use give us estimated pressures. These are useful indeed we use them a lot.

[Teddy (punchie)]

Not clear from your post what the issue is, but Just because there is not load data for a particular bullet does not mean there is a problem. Similar bullet, slightly heavier and similar bullet, similar case capacity can be used to find a safe starting point.

Yes this is the best way. Data and start lower not too low.

Read a good manual. Should be a section on pressure and signs of too high.

Primers is one way, kick or recoil is another if you are used to shooting this
firearm. Recoil should be normal.

[uscra112]

Without expensive equipment the best you can do is measure velocity and compare to the most similar cartridge/load/bullet/powder for which you can find pressure data. For instance, I load cast bullets in a 30 BR long, I compare my velocity to 30-30 and 300 savage pressure data or max load data with the same powder and similar or the same bullets.

This must not be extrapolated to cover different powders, since fast powders must necessarily generate higher peak pressures for a given MV than slower ones. Velocity is responsive to Specific Impulse, which is pressure AND time related. Technically speaking it is the integral under the pressure/time curve from ignition to the point where the bullet exits the muzzle.

[Larry Gibson]

This must not be extrapolated to cover different powders, since fast powders must necessarily generate higher peak pressures for a given MV than slower ones. Velocity is responsive to Specific Impulse, which is pressure AND time related. Technically speaking it is the integral under the pressure/time curve from ignition to the point where the bullet exits the muzzle.

Excellent observation.

[dtknowles]

This must not be extrapolated to cover different powders, since fast powders must necessarily generate higher peak pressures for a given MV than slower ones. Velocity is responsive to Specific Impulse, which is pressure AND time related. Technically speaking it is the integral under the pressure/time curve from ignition to the point where the bullet exits the muzzle.

Agreed, must compare to data with the same powder and very similar bullet type and weights. Also consider barrel length and be conservative since we are just estimating.

Regarding area under the curve, I am not sure many members are familiar with analytical geometry or calculus. Yes, like Larry said, excellent observation. Just to throw some more into the mix, the area under the curve is PSI-Seconds. If you multiply PSI by the bore cross sectional area you get force, force times time is impulse. In theory you should be able to calculate velocity based on impulse but the drag of the bullet in the barrel is poorly understood and depends on many variables.

Tim

[dtknowles]

I am a retired engineer who had worked with calibrated equipment a lot. It is my opinion that there is no way to properly calibrate high pressure measuring equipment as there is no primary high pressure standard. The methods we use give us estimated pressures. These are useful indeed we use them a lot.

I too am a retired engineer, but I am back working again on fun projects. Kind of depends on what you consider high pressure. We use calibrated test equipment rated for 30,000 psi. We are calibrated to a tenth of a percent across the whole range of 0-30,000 psi. We have to burst test 10,000 psi helium tanks; we must show a burst factor of 2 so we have to show they don't burst at less than 20,000 psi but we still have to try to burst them because we have a leak before burst requirement. This is for design verification. We also have to proof test all the production tanks to 15,000 psi. This must all be done with instrumentation that has NIST traceable calibration.

We could calibrate Larry's system up to 30,000 psi if he had a barrel threaded to accept a connection to our pressurization system.

Here is a for instance but this one is only good to plus or minus 0.2% of full scale.

https://www.coleparmer.com/i/additel-digital-pressure-gauge-0-to-40-000-psi-autoclave-m-250-c-connection-0-2-full-scale-accuracy/6833684

Tim

[414gates]

Use a 1/10,000 micrometer.

You need to start with virgin brass. Measure the base diameter just ahead of the extractor groove.

After firing, measure again. Method attributed to Vernon Speer.


https://youtu.be/w1OJy5958iU

Addendum :

This method does not measure absolute pressure. It gives an accurately measurable pressure comparison between loads, that works on any cartridge.

[TD1886]

There is only one way to measure pressure and that is to have the proper instruments to do so.

Similar case volume isn't good enough. Just a different shoulder angle on similar volume cases can throw the pressure way off.

Similar bullet? Don't bet on that either. Many loading manuals will tell you not to swap a same caliber and weight bullet brand X with brand Y. Just a different lenght bearing surface can play havoc with pressure as can a different bullet jacket alloy.

Yes powders have burn rates. As Larry noted burn rate isn't calculatted with cartridges, it's closed bomb test. When the powder is inside the cartridge case the whole game changes and there are far too many things to name here that change it. Also don't assume different burn rate powders stay in the burn rate when compared to another powder that shows a slower or faster burn rate. Depending on the cartridge and the bullet they often switch places. To name two that switch places in this manner are 4198 and 4895 and there are more.

Don't bet your life on primers, a very bad way to just high pressure. Measuing expansion of the solid web portion of the case is a better thing. Again the best way is with pressure measuring instruments.

The only thing I can say about Quickload is that it can get mighty close. Like Larry said garbage in garbage out, but if you feed it all the right data it's very close. Those of you that have it know all the different data that can be inputed to it.

[dtknowles]

There is only one way to measure pressure and that is to have the proper instruments to do so.

Similar case volume isn't good enough. Just a different shoulder angle on similar volume cases can throw the pressure way off.

Similar bullet? Don't bet on that either. Many loading manuals will tell you not to swap a same caliber and weight bullet brand X with brand Y. Just a different lenght bearing surface can play havoc with pressure as can a different bullet jacket alloy.

Yes powders have burn rates. As Larry noted burn rate isn't calculatted with cartridges, it's closed bomb test. When the powder is inside the cartridge case the whole game changes and there are far too many things to name here that change it. Also don't assume different burn rate powders stay in the burn rate when compared to another powder that shows a slower or faster burn rate. Depending on the cartridge and the bullet they often switch places. To name two that switch places in this manner are 4198 and 4895 and there are more.

Don't bet your life on primers, a very bad way to just high pressure. Measuing expansion of the solid web portion of the case is a better thing. Again the best way is with pressure measuring instruments.

The only thing I can say about Quickload is that it can get mighty close. Like Larry said garbage in garbage out, but if you feed it all the right data it's very close. Those of you that have it know all the different data that can be inputed to it.

yes, and no. I was talking about cast lead bullets and when I say similar, I mean alloy, weight and bearing length. I am not buying the idea that shoulder angle will make enough difference to be noticeable against all the other uncertainties. I am also talking about ballpark pressure estimates not precise pressure measurements. Just trying to ballpark a starting load and some idea when a load might be sneaking up on max. pressure but considering these are cast bullet loads, I don't really expect to be getting anywhere near the gun's capability. I am not going to be shooting cast bullets at 60,000 psi. I you have a cartridge with little or no load data, you use the data you have and a bit of judgement.
I get no measurable head expansion on my 30br brass with cast bullet loads. That is no help on estimating pressure, and it does not help on picking a starting load, you have to pick a load before you can fire a shot to measure head expansion.

I don't use Quickload or other such programs. I am comfortable using similar loading data and some judgement.
Tim

[TD1886]

yes, and no. I was talking about cast lead bullets and when I say similar, I mean alloy, weight and bearing length. I am not buying the idea that shoulder angle will make enough difference to be noticeable against all the other uncertainties. I am also talking about ballpark pressure estimates not precise pressure measurements. Just trying to ballpark a starting load and some idea when a load might be sneaking up on max. pressure but considering these are cast bullet loads, I don't really expect to be getting anywhere near the gun's capability. I am not going to be shooting cast bullets at 60,000 psi. I you have a cartridge with little or no load data, you use the data you have and a bit of judgement.
I get no measurable head expansion on my 30br brass with cast bullet loads. That is no help on estimating pressure, and it does not help on picking a starting load, you have to pick a load before you can fire a shot to measure head expansion.

I don't use Quickload or other such programs. I am comfortable using similar loading data and some judgement.
Tim

All I'm going to say is shoulder angle can make a huge difference. The 6mm Creedmoor and 6.5 Creedmoor are two newly engineer designed to burn powder more efficiently and in hopes of burning most of the powder inside the case rather then in the bore. I have the 6.5 Creedmoor and I'll say that they are correct as I've had some "different" things happen when using powders I've been using for many many years. But anyways I understand what you are saying.

[racepres]

A Chronograph is relatively inexpensive...
If yer getting more velocity than everyone else...you are at Higher Pressure...

[414gates]

I am also talking about ballpark pressure estimates not precise pressure measurements. Just trying to ballpark a starting load and some idea when a load might be sneaking up on max.

When you have a cartridge for which there is no powder data, such as yours with cast bullets, you can consult the cast bullet reloading manual and find a rifle cartridge with case capacity very similar, and bullet weights very similar, and use the starting powder load.

A quick search says the 30BR has the same case capacity as the 30-30.

30-30 cast bullet load data can reasonably be tried for the same bullet weight.

[dtknowles]

When you have a cartridge for which there is no powder data, such as yours with cast bullets, you can consult the cast bullet reloading manual and find a rifle cartridge with case capacity very similar, and bullet weights very similar, and use the starting powder load.

A quick search says the 30BR has the same case capacity as the 30-30.

30-30 cast bullet load data can reasonably be tried for the same bullet weight.

That is exactly what I did. Worked out just fine.

Tim

[P Flados]

Another retired engineer type here. I use Quickload (QL) quite a bit. I have checked it against published load data a lot.

The tool can be very good for most applications if the user knows what he is doing. The biggest exception for QL accuracy is probably revolvers. QL does not even try to address cylinder throat length and cylinder gap. The next item is that QL will never be able to do is predict "spikes" from non-uniform ignition/burn. I also do not trust QL with high powder compression and there is at least one powder (Lil Gun) that just does not seem to perform as modelled.

Excluding the above, if you do real good at the inputs, my bet is that you get better results with QL than with using published data that is not quite exact for your load.

The most significant "avoidable errors" will usually be related to percent fill. Case capacity, case length, bullet length and COAL are the raw inputs to get this one parameter. If you get percent fill very close to either QL or to the as tested configuration for published load data you get rid of a lot of potential error.

The remaining factors are things like chamber dimensions (loose vs tight, gas leakage around the bullet before engraving, and distance for bullet movement before engraving), bullet resistance as it engraves in the rifling, primer affects, and powder burn rate variations.

With QL, you can "benchmark" your load by measuring velocity, adjusting it to muzzle velocity, and then going back in and adjusting the QL value for powder burn rate (Ba). This will tend to do a "one size fits all" correction for any inputs that were not quite right.

With good inputs and a good benchmark, the QL estimate of pressure for most loads will probably have an error that is in the same ball park as the error with something like what Larry uses. I say this not because the QL predictions will be that "great". I say it because of the accuracy limitations with the available measuring system for something as messy as chamber pressure.

[TD1886]

Another retired engineer type here. I use Quickload (QL) quite a bit. I have checked it against published load data a lot.

The tool can be very good for most applications if the user knows what he is doing. The biggest exception for QL accuracy is probably revolvers. QL does not even try to address cylinder throat length and cylinder gap. The next item is that QL will never be able to do is predict "spikes" from non-uniform ignition/burn. I also do not trust QL with high powder compression and there is at least one powder (Lil Gun) that just does not seem to perform as modelled.

Excluding the above, if you do real good at the inputs, my bet is that you get better results with QL than with using published data that is not quite exact for your load.

The most significant "avoidable errors" will usually be related to percent fill. Case capacity, case length, bullet length and COAL are the raw inputs to get this one parameter. If you get percent fill very close to either QL or to the as tested configuration for published load data you get rid of a lot of potential error.

The remaining factors are things like chamber dimensions (loose vs tight, gas leakage around the bullet before engraving, and distance for bullet movement before engraving), bullet resistance as it engraves in the rifling, primer affects, and powder burn rate variations.

With QL, you can "benchmark" your load by measuring velocity, adjusting it to muzzle velocity, and then going back in and adjusting the QL value for powder burn rate (Ba). This will tend to do a "one size fits all" correction for any inputs that were not quite right.

With good inputs and a good benchmark, the QL estimate of pressure for most loads will probably have an error that is in the same ball park as the error with something like what Larry uses. I say this not because the QL predictions will be that "great". I say it because of the accuracy limitations with the available measuring system for something as messy as chamber pressure.

I have to agree with you. Many people don't know all the data that can be inputed in Quickload like case water capacity, bore dimensions even groove measurements, in addition to fired case and sized case (especially for water capacity). It comes very close for not actually measuing the actually fired pressure and chronographed velocity.

[racepres]

You Cats enjoy yer Theory, and Computer models...Meanwhile...I remain Blissfully Ignorant...and Shoot Alot..
Aint blowed Mesef up since the '70's... I believe I will be Just Fine!!!!

[Larry Gibson]

You Cats enjoy yer Theory, and Computer models...Meanwhile...I remain Blissfully Ignorant...and Shoot Alot..
Aint blowed Mesef up since the '70's... I believe I will be Just Fine!!!!

Seems we all managed to do that....not blow ourselves up. However, the ability to measure pressures or to closely questimate pressures gives us another tool to save components and to continue to not blow ourselves up.

[TD1886]

Seems we all managed to do that....not blow ourselves up. However, the ability to measure pressures or to closely questimate pressures gives us another tool to save components and to continue to not blow ourselves up.

Amen to that!

[dtknowles]

yeah, start low and work your way up but why start way too low.

Question, does everyone else always start with the manual starting loads? I confess, sometimes I start halfway between starting and max. Sometimes I use the starting load and if it is accurate I don't work up at all. Horses for courses.

Tim

[racepres]

yeah, start low and work your way up but why start way too low.

Question, does everyone else always start with the manual starting loads? I confess, sometimes I start halfway between starting and max. Sometimes I use the starting load and if it is accurate I don't work up at all. Horses for courses.

Tim

Sometimes... especially for Contender or Ruger's

[P Flados]

yeah, start low and work your way up but why start way too low.

Question, does everyone else always start with the manual starting loads? I confess, sometimes I start halfway between starting and max. Sometimes I use the starting load and if it is accurate I don't work up at all. Horses for courses.

Tim

I used to to some extent, but was also likely to start mid range with a "high margin" gun.

Most of my workups in recent years have been for loads where I did not have exact matches for the bullet and/or did not have load data with a published "starting load". Many of these loads were also never intended to be worked up to max SAAMI pressure. Frequently I have used Quickload and started my workup at a predicted pressure at the low end of the range I wanted to be in.

[justindad]

I start low when loading boolits for which there is no load data. If I have the exact bullet shown in the manual, I usually start in the middle. Bullet design can have a surprising affect on pressure, due to factors in addition to weight and net case capacity. I’m starting to suspect multiple lube grooves can drive up pressures.