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Pressure Trace Projects

Pressure has always been a mystery to me. I have read everything about case measurements and reading pressures from fired cases. Always a concern, and it seems we as hand loaders are still in the dark on some of the mysterious happenings inside our chambers! I know I was, and still am to some extent. 

A few years ago, even before the B&M were thought of, I found a system called the Pressure Trace, by RSI. Recreational Software, Inc.

http://www.shootingsoftware.com/pressure.htm


I had been using the RSI shooting software for a couple of years, one of the few software companies that have shooting software for "apples"! Yep, I am a "Apple" guy! I started looking at the Pressure Trace System they offered, price was reasonable, so I decided to give it a go. Of course, I had to work from a Windows System, unfortunately, so that made it a little unfriendly to a Apple guy, but I seemed to manage my way around it. After some trial and tribulation I was reading pressures or pressure estimates on some of my favorite loads that I had used for years in 358 STA, 458 Winchester, 458 Lott, 45/70 and others. It was fun. But I was taking it far too seriously and trusted the system far too much to begin with. I was having secondary peaks that were crazy, 100'000 PSI and nonsense, while primary peaks would be where they were supposed to be. Being somewhat "Compulsive Obsessive" about some things this was driving me insane. Had several very very long conversations with Jim Ristow, of RSI about the secondary peaks, and still I was not so sure about this phenomena. Did not matter, factory ammo, my hand loads, everything was giving me readings I did not agree with, and that the case measurements did not indicate, nor any other normal pressure signs.


After much consideration I, on a fluke decided to scrape off the strain gage and replace it with a new one. I took all the measurements needed to set up the barrel perfectly, took a lot of time with this one, made 100% sure everything was set up right, everything was working proper. Shazam!!! Secondary peaks disappeared, strange happens disappeared, anything out of order disappeared! I had not done a good job setting up the strain gages the first go around, so I was getting wild readings, can anyone here say and remember "Operator Error"? That was me, Operator Error!


On any of the other rifles I was doing test work on that was giving strange readings, I took a pocket knife, scraped those strain gages off, and replaced them all. Yes the strain gage can be removed from any rifle with a little acetone or similar product without using a pocket knife and scratching up your rifle, but I needed to expedite, I did not have time for such "niceties". All my Pressure Trace work started to look proper and fell in line with what I was seeing from case measurements and other indicators of pressure. This was actually working, and as best I could determine it had to be pretty close to real numbers in PSI. Exact? Well, probably not, but what system really is? I would venture to say that with an individual rifle that it is coming in very close, and close enough that you should pay attention to what it tells you!


At the end of 2005 I started working with the B&M series of cartridges. Honestly, I was a bit lazy about working with the Pressure Trace, decided I would just do case measurements and study other pressure indicators to develop the cartridges. I did this on the 50 B&M, 50 B&M Super Short, 458 B&M and the 416 B&M from the start. That in itself was a learning experience as the B&Ms work from RUM brass, no big belted case to work with? I had to learn a new system of case measurement, and even had to create it myself as I went along. On the bigger bores I first decided that a .0015 increase in case size from unfired to fired was about right. Then I had some go to .002, but everything looked very good, no possible signs of pressures. Then to .0025 increase, then anything that went much above that was beginning to show other indicators, never had a stuck case, or even a sticky bolt. Smooth was the word, so I stopped at .0025 increase, this is with fired cases too, not new cases. New cases would always go over the allowed amount.


Well Aaron Carter wanted to do an article on the 458 B&M. Aaron is a young fellow and maybe back then a little green around the gills, but a fine young man none the less. Aaron had some concerns about pressure, even a long conversation we had I was not able to convince him the 458 B&M was actually safe with the loads I was shooting. Of course take a look at the 18 inch 458 B&M and folks do wonder how you can get performance like that out of such a tiny gun.


OK, I agreed to get off my duff and start doing some pressure traces with the B&Ms. I got all the strain gages attached, took all the right measurements, took my time to get things set up exactly right. And wow was I apprehensive about squeezing those first rounds off! What if I was all wrong? All the work I had done, what would I do if it was all over pressure?


Well the story turns out excellent. I started shooting and testing, which took several weeks to accomplish. And it appears that I was spot on the money across the board with the various B&M Cartridges. The Pressure Trace worked perfectly, gages were perfect, no wild strange second peaks or other readings, pressures were falling into place and most all well under what I had thought they might be. I was in great shape, even able to increase velocity of some loads, in a safe manner.


Aaron was happy with the findings on the 458 B&M, and did the article and considered himself safe by doing so.


I was able to prove to myself at least that what I had done was correct, I had figured out the mysterious case measurement study, at least for the B&M cartridges at that time. And found the Pressure Trace to be an immensely valuable tool for working with these cartridges, which are a great unknown.


All of the pressure readings listed with all the B&M cartridges come from the Pressure Trace System. I can't tell you whether they are 100% exactly perfect or not. I can tell you that I trust the system, and from everything I can compare with it matches up with reality as best I can determine. After a year or so of being lazy with it again, I am back to work with it and it has told me some truly amazing things in just the last couple of weeks.


Just to give you one example with the new North Fork 450 gr CPS in .500 caliber in the 50 B&M. Normal load out with 500s and 470s has been 70/IMR 4198. I just put 71/IMR 4198 with the 450 North Fork, I knew that was very safe, and did the test work at 2220 fps or so in the 50 B&M. Now with the Pressure Trace hooked up I decided to give it a try, and found I was low at 51000 PSI. So I bumped it to 73/IMR 4198 for a velocity of 2280 fps at 55000 PSI! I was amazed at this, so I went to 74/IMR 4198 for over 2300 fps and 59000 PSI. Now 75/IMR 4198 for 2340 fps and 61000 PSI! This was incredible, but I had to try one more time, 76/IMR 4198 gave me 63000 PSI and 2365 fps. I was astounded, and would have never taken things that far without being able to measure increasing pressures as close as the Pressure Trace can. All other indicators agreed with the Pressure Trace. Thing is, I ran out of case capacity at 76/IMR 4198!


I found the Pressure Trace System one hell of a good tool that any Hand Loader can add to his tool pouch. I will continue to do test work and load data on all the B&M Cartridges as we move forward. I have attached a strain gage to the 9.3 B&M, so that data should start rolling in over the next week or two. 

The work done with the 50 B&M and the 450 gr North Fork CPS.

450 NF CPS Pressure Data.pdf

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