Pressure Testing and Ballistics Software for Reloaders?

S

Savage_The_Barbarian

New member
I have been reloading many calibers for many years. Rifle and pistol mostly and I have the Single Stage presses as well as the Hornady LnL AP fully dressed with "load bins" for each caliber, that way I do not have to adjust this or that for every caliber I load on the AP. Initial adjustment of all the parts then I am done. But the "load bins" are expensive because you duplicate a lot of items.

Anyways, back to the subject. I finally decided to do some real pressure testing on my loads. I have looked at pressure testing receivers and barrels which are way too $$$$$ and then there is the strain gauges with the RSI software.

I originally wanted to use a piezometer and then find a software package to read the information or having a O Scope to do the same once it is all calibrated. Of course the piezometer requires the drilling of a hole in the pressure barrel (ouch $$$ to buy one or do it yourself for less). This to me seems like developing a whole new software package unless there is something out there that I am not aware of (which there probably is).

So because I want to get something that is affordable but yet desirable because it will give accurate pressure traces, does anyone have another recommendation for a ballistics testing package that will give accurate pressure readings without breaking the bank?

TIA
 
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Just get the RSI unit. It works fine. Board member Denton Bramwell (a physicist who makes his living in statistical manufacturing control systems) did a statistical test on results from piezoelectric and copper crusher systems and found the strain gauge most repeatable and accurate. If you buy SAAMI reference cartridges, you can calibrate it to match SAAMI equipment.

If you take a conformal piezoelectric transducer, as used by SAAMI and a channel transducer with diaphragm in a hole drilled at the case mouth (EPVAT standard) or a channel transducer drilled at the CIP specified location, and you measure a reference lot of .223 ammunition that just happened to be just exactly at maximum (unlikely in real life), you will find the conformal transducer reports 55,000 psi and the channel transducers report 62,366 psi. So, you can see that accurate "absolute" pressure is problematic to measure.

National Instruments and several other outfits have test systems available with high speed A to D conversion and high speed data buffers that will capture and store a trace, regardless of whether it is piezoelectric or strain gauge measuring. It will give you more resolution than the Pressure Trace (8-bit), but whether that has any real value or not is doubtful as shot-to-shot variation is greater than the resolution of the system.
 
Thanks for that excellent presentation on this. I am looking forward to reading the linked article and if I have additional questions, I will post them here.

Again, this is great information. I hope that I am smart enough to digest the entirety of it. Being an engineer, I will have to put on my physicist cap to absorb the information.;)
 
Unclenick
Just get the RSI unit. It works fine. Board member Denton Bramwell (a physicist who makes his living in statistical manufacturing control systems)
Click to expand...

I think Denton has an EE degree.
I have been debating him on the internet for over a decade.

I could go on and on about strain gauges, the NIST, and the path between.
Roark's formulas, the strain gauge placement error, and SAAMI registration pressures kill the deal. I can design instrument amplifiers with plenty of accuracy. I can buy storage scopes with lots of accuracy.

I will cut to the chase: Never mind pressure cannot be measured well. Pressure does not matter. It is the effects of pressure that matter. Those effects can be measured. In strong firearms the brass is the weak link. Brass before and after firing is in a static state that CAN be measured. A pair of calipers, pencil, and a piece of paper is enough.

I could go on and on about the rates that EE consultants charge vs ethics.
It gets to be more like poker than business or science.
 
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I agree that the brass plays one of the most crucial roles in this and have been using the brass/chrony methodology for years. I do a lot of plotting and developing formulas for my loads and this is more for use as a helping method for estimating the pressures.

I do realize that pressures are uniquely variable and should never be used as a single source of information. However, I think that the added benefit will be helpful to me for the direction that I am heading in at this time.

A small cost to put out to potentially save my various multi thousand dollar rifles.
 
I read Bramwell's article. I'm just a dumb ol' biochemist, but I think I understood most of it (just don't make me take an exam on it). I found it pretty informative, and not so bogged down in minutiae that it was difficult to read.
 
Steve, there is a 3rd EE that is into that, that argued with Denton more than me.

I have my own system. I measure the Mauser, belted magnum, or 222 case head around the extractor groove with dial calipers. I fire it. I measure around again. If there is any change, I have gone too far. I need to back off between 3% and 6% powder charge depending on the powder used. If the limit is loose primer pockets, my system is better than firing the same case a few times and feeling for a change in primer insertion force. It is counter intuitive, but extractor groove growth is a better indicator for the threshold of loose primer pockets than loose primer pockets. So far I have no converts.
 
I have the RSI system.

I like it more in theory than I do in reality.

The gauges are difficult to place correctly. More "delicate", I guess, than "difficult" but you can count on having several of the $30+ gauges as "almost but not quite" before you get it right. Getting it oriented correctly, with no air bubbles and not stuck to... what ever touches it.... is no trivial task. As it turns out, super glue (you have to use a specific kind, see below) on smooth gun barrels is very slippery at first, like oil.

Measuring the barrel thickness at the gauge location is a critical and very much non-trivial task. It can be done, yes, but it requires tools and techniques that most reloaders will not need or have for any other purpose.

On a great many firearms, there is no "correct" place that meets all specified criteria as outlined by RSI. For instance, on a Savage rifle, the barrel contour, the barrel nut and the cartridge length and profile all can conspire against you. The gauge CAN be placed past the cartridge, down the bore a bit, but then you miss the first microseconds until the bullet passes the gauge.

The first place I wanted to use the system on Ruger M77 MkII in .204Ruger.

I had numerous emails back and forth with Jim at RSI. He is friendly and helpful, provided me with plenty of information and theory. (He also *hates* QuickLoad. HATES, all capital letters, H-A-T-E-S)

Unfortunately, Pressure Trace and QuickLoad disagree quite severely. QuickLoad, by the way, is much closer to the expected pressures according to published load data.

Now, there are reasons for this. .204 is a very small and short cartridge. The barrel walls are very thick. My gauge placement technique probably could have been better.

I went over it all with Jim. He's most likely right and tried very hard to be helpful and attentive. Real nice guy.

However, that doesn't make me confident in the pressures I get from the system on that gun. *THE* gun I most wanted pressure from. :(

Another problem is the glue. You have to use special varieties. They aren't found in stores, normally. You usually have to order more every time you mount a gauge because it can only be stored a few weeks. That's OK if you want to or can place all your gauges at once but it's not so OK when you get a new gun and have to order more glue. Big pain. If you order more gauges, they come with more glue but if you don't mount them all in close timing then you need to order more glue later anyway.

Anyhow, long story short, I love the idea. I'm sure it can be made to work very well and very accurately if you have both the time and money. You'll eventually develop an expertise for placing the gauges and learn the intricacies of the system... but it's anything but "plug and play". I just don't have time for it.
 
extractor groove growth is a better indicator for the threshold of loose primer pockets than loose primer pockets. So far I have no converts.
Click to expand...

No converts? Before the Internet it was common for reloaders to use case head expansion. Back then reloaders knew factory loaded ammo had been tested. They understood case head expansion was considered acceptable at .00025”. Now we have the reloader discoverers. They discovered? Case head expansion of .0005” is too much.

Back then a few used a primer pocket gage. It only worked if the reloader measured before and again after firing. Logic, if the primer flash hole increased in diameter during firing the case head expanded, the primer pocket hole expanded and the case head crushed/shortened.

Then there are shell holders, some fit, some don’t. My favorite shell holders are the ones that do not fit. I use the loose fitting shell holders to size cases for short chambers.

F. Guffey
 
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