Sometime back, a gentleman from this forum sent me his Pressure Trace response and I sent back a Quickload comparison. I was a little disappointed with the shape of the Quickload response but the area under the curves are within 8.6% of each other.

In a data acquistion system, a key parameter of interest is the linearity of the measurement system. If the strain gauge is operated over its linear range (or known non-linearity) then the measured values, relative to each other, are accurate. This means the shape of the curve is accurate with possibly an unknown scale factor due to the various gain errors mentioned previously.

If the velocity is measured, abeit to within some tolerance, then by scaling the integral of the pressure curve vs time, ie the velocity, seems like the peak pressure could be quite close.

Because Quickload has the ability to shape the burn curves of powders and takes into account start pressure, case shape, etc, when it calculates the velocity, I would fit Quickload pressure vs time curve to the measured data.

Then the simulator can be used to predict other weight bullets using the same powder and similar case design more accurately, good for wildcats.

rgds,

steve

Federal Cartridge Company was one I had talked to about pressure data for a specific lot# of ammo. The guy I talked to, Gary I believe, said he wouldn't get me the data on an ongoing basis, but he'd have the head ballistics engineer go back and look up some lots I was going to make some comparisons with. I've not pursued it though.

Unless my barrels are actually tighter than SAAMI spec'd tight barrels, I'll always see a lower pressure number than them anyway. I've shot probably as much or more factory ammo in various rifles with the M43 and PressureTrace hooked up to say for certain that I never exceed, and mostly fall just shy of SAAMI max for the specific cartridge tested.

If you've tested as many factory cartridges as I have, you feel very comfortable about loading up wildcats with not much to base them on, I do, but it's based on actual testing. My M43 and PressureTrace are falling within 0-2k psi of each other when rifles are equiped with two gages and testing is performed simultainiously.

When someone has done the extensive testing and analysis that I have, it's not too hard to see the obvious.

Tell me if you see anything interesting in this print...
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Data for the above PT test.
That 30/338 LI plot looks familiar.

Here's a load we tested the last time out for an example.

These two tests were performed simultaineously. Right now I forget why PT didn't have the last shot recorded on it.
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Brent,

you made my day!

rgds

steve

Brent,



the load was:178gr A-Max 30 cal, 95.0gr RL25 Federal 215M, OAL is 3.702", bullet length is 1.305". and you had mentioned the length of the data record was 1.5msec, so I just took that number and divided by the number of points to get the stepsize as there was no time index in the file.



If we can sort this out, i will change the post, otherwise i will delete as i do not want to show bad info.



rgds,



steve



PS. Brent, i used shot 1 in the data file and I just re-opened and notice that there is a series of shots and i just assumed the first one was for the RL25 but now i see probably bad assumption on my part. Let me know and i will redo the plot or delete. Thanks



steve

Steve,

Here's the screen shot from that test there.
First shot was a tad higer than the others on this one, clean barrel likely. Anyway, something to associate those numbers with. You might find another trace (shot) more representative though. That load was between 3365 and 3404 fps too. I ended up getting 3550, but I had to go to Retumbo. 3520 or so was a good safe load about 65k psi.

Are you sure there's no MS time referance associated with each of the micro strain numbers? I'll have to look at the ini. file again.

Brent,

the problem was the time record in the data file is always for the max. time of 2.5mSec and not the screen setting. You thought the pressure might be 5k higher, so i used that number in the previous graph. Here is your original raw data, using 2.5mSec. Not to shabby!

Similar velocity and the simulator has a little bit of pressure guardband so as not to get me in trouble. Thanks.

I purchased a Pressure Trace unit from RSI at the beginning of the summer. Since then I have received EXCELLENT customer service from RSI. It was delivered within the time promised, which is a big thing these days especially when you live in Canada, but order from the USA.

Jim Ristow, in particular, has provided me with above and beyond service. He is quick to answer my questions and provide guidance as to solutions for any issues that may arise, be it hardware or software.

I would highly recommend that anyone wanting to purchase ANYTHING from them, to do it. They back up their claims and then some!

I would also like to add WELL DONE JIM! I received the replacement plugs, and plan on fixing my gage and getting out shooting this weekend. I�m one happy customer!!

Neil Gauthreau
(AKA Turok)

Steve,

Ya lost me on the the problem was the time record in the data file is always for the max. time of 2.5mSec and not the screen setting.
You know that raw data better than I.
Looks like a good match though, bet that�s nice to know.

Once I got the two gage setup on the 30-338 Lapua Imp I saw no difference in it or any of the others I tested, just the 6.5 WSM we were first testing with the M43 and PressureTrace. It was resolved, or partially resolved. Something to do with the PT gage we had located on the barrel. My Dad removed the gages before I had the opportunity to look into it further once we found all the other rifle�s pressures matched up on the two units.

We immediately decided it has to be the gage, or it�s bond, or it�s location. All I know was that the two gages were not in the exact same location over the chamber and one was further forward. One gage was up on top, the other was hidden under the barrel in the fore end and I didn�t see the difference between them.

I suspect I measured the midway point from the case shoulder to the front of the receiver for one gage, but from the front of the Tubb recoil lug on the other. It�s just a guess, but I never saw the two before he removed them both, so I don�t know which gage was forward of the other, Dad did say one of them was more forward though�

I had concerns that the way the calculations were being done was the reason for the pressure disparity in units, and as Burt and Jim can attest, I bugged them and Ken Oehler relentlessly to try and understand what was going on, and which units formula might be incorrect. I did learn, and verify many things while this was going on for quite some time. Burt was steadfast that his formula�s were correct, and the problem indeed lied somewhere else, which led me to set up multiple barrels with two strain gages each to gain more insight into this disparity issue.

Once I abandon the idea I might could use a gage over the receiver ring of my 30/338 LI and get any reliable info from it for when I was ready to put the barrel in a block, I installed another gage where I should have had it the whole time, across from the other gage on the barrel. All the readings between the M43 and PT were now easily falling within 2k psi, not at all what I had experienced with the 6.5 wsm. Then we began testing on the other barrels, same thing as the 30/338 LI was showing now, all within 2k psi on every test. Boy, at this point was I glad to see this! I was however, perplexed by the 6.5 wsm�s disparity when the other barrels were all well within reason. The only time I�d even get the up to 2k psi disparity was at lower load levels, like 36 -58k psi, above that for the most part, pressure levels fall on top of each other damn near all the time.

By then, we�d collected a wad of new info on the 6.5 wsm and the throat was eroding pretty good and is now apart getting the barrel set back, so the gages were removed until it�s done. I�m pretty sure that the PT gage was either defective, had a poor bond to the barrel, or located incorrectly too near the case shoulder, as the pressure it indicated was too low for the pressure signs we got on the top loads, and the M43 pressures were about what I had expected them to be.

We had a hick-up in the beginning, but we�re on track now.



Ditto what Turoc said, ten fold!!!!!

Setting �the new standard� in top shooting/reloading products for the average shooter, customer service, and support are what these two guys are up to, and ALL about!!

Brent,

Thanks for all the info! I appreciate the feedback using real world data. I do not see myself getting to hardware instrumentation and that is why I focus on simulation. Sad.

The data file has 250 points. And i noticed on your plots, you can choose plotting scale of .5, 1.5 or 2.5mSec. 250 and 2.5mSec sounds like a match. So I am assuming the system is set to sample at 10uSec/reading for a total of 2.5mSec, always, and the plot is only for zooming in to finer time scale. At least this is the way I would design it as 2.5mSec should always be longer than the muzzle exit time of any practical rifle (do not know about air gun ).

The first modelling was using 338 Lapua dimensions and just set the diameter for .308 and ran the sims. When this was not a good match, i lost interest feeling that something was inconsistant but not having enought info to pursue.

Now that time scale issue has been resolved, i went back and modelled the 30-338 Laupa Improved using the dimensions you sent me earlier. I picked shot 6 because it was slightly below the average peak pressure reading and in Quickload, i only adjusted the shot start pressure to match your starting pressure. The curves now match very well, with a slight difference in the tails. Your data set integrated out a velocity of 3431fps and Quickload 3238fps.

best regards,

Steve