I'm lugging more and more stuff to the shooting bench. The latest piece of equipment, thanks to the Yukon OK boys is an RSI pressure trace unit. Unfortunatly I had to provide my own lap top [img]/ubbthreads/images/graemlins/crazy.gif[/img]
After setting it up on the kitchen table, last night, and clicking the strain gage w/the button of a ball point pen and getting a trace for each click I figured I was in business.
I then installed the strain gage on the barrel chamber according to instructions.
I set up the data for the chamber and barrel as best I could with vernier caliper and a good guess at the chamber diameter at the proper location.
Loaded up two stiff loads of 89gr IMR-7828 and 250gr SMKs. These are a full grain over the last ones I shot. Velocity was in the mid 28XX area. But wo is me, no pressure trace.
A quick phone call to Burt @ RSI Manufacturing gave me enough confidence to mess with the trigger settings on the unit. As is normal for me, I adjusted for the maximum sensitivity.
WaLaa- Pressure trace displayed. Wooo Hooo. Max pressure 58XXX, which seemed reasonable. No extraction or bolt opening negative symptoms whatever. The 250 SMK went across the chrony @ 2858 FPS.
I did note a bit of a secondary pressure spike about 3/4 way down the trace. Interesting, says I? I don't like those things though I hear they are normal for the RUM cases but don't have valid data, yet.
Second shot was again 89gr 7828 but w/Hor 225 SPs. Pressure went to 60XXX and a velocity of 2999. I figure that the increase in pressure with the lighter bullet is due to the Hornady being seating at least touching the rifling while the SMK is jumping just a little to reach them.
I lost the first trace due to not being able to see the computer screen clear enough in the sun light to know what to do when.
I have the second trace saved.
Initial opinion:
Its good. Discussion w/the manufacturer, a small shop, indicates they've done their home work. The more accurate the measurements entered during setup, the more accurate the pressure reading.
The unit is simple and straight forward to use.
And for us nerdy/geeky/anal/hungry for data types, I'd say its a must to have.
More data will be forthcoming as I proceed with this flash tube idea.
I plan on ordering one soon - I think it's an interesting tool. The achilles hill of the PressureTrace is calibration. But if you knew the pressure of a load, you wouldn't need PT.
[ QUOTE ] As is normal for me, I adjusted for the maximum sensitivity.
WaLaa- Pressure trace displayed. Wooo Hooo.
...
I did note a bit of a secondary pressure spike about 3/4 way down the trace. Interesting, says I? I don't like those things though I hear they are normal for the RUM cases but don't have valid data, yet.
[/ QUOTE ]
The 2ndary spike is likely an artifact of having the gain too high. I'd back off the gain as much as possible, otherwise you're amplifying noise and subject to artifacts.
I plan on calibrating my guns by increasing loads until I see physical pressure signs. Once the unit is calibrated you can more easily compare powder, primers, loads at various temps.
I got 5 traces just closing the bolt [img]/ubbthreads/images/graemlins/blush.gif[/img] Trigger/Sensivity set to 0. The manufacturer says that when set to zero his is triggered by low flying aircraft. I'll increase the setting (decrease sensitivity/trigger setting until it just triggers.
Need a little input here, seeing as how this is a community effort...
Goal: to compare pressure traces and accuracy between cases fitted with flash tubes and cases w/o flash tubes. I expect to see differences in pressure, SD, ES and accuracy. Previous testing w/the Win Mag showed improvement in all of these areas.
Question: I'm thinking to work up a base load to compare to with the flash tube installed. What would be the best way to develope a comparison load w/o the flash tube? Load to same velocity? Same pressure?
What I learned from the Win Mag experiments is that I don't want to shoot the same load with the tube, without the tube. Had to hammer the bolt open when I did that......
Any recommendations will be seriously considered and probably used.
Honestly, I would think either one would work. Your wanting to compare velocity vs. pressure so it really doesn't matter which way you do it. If you find that @ the same pressures, the velocity of the FI case is more, or if @ the same velocity the pressure is less in the FI case, you've discovered the same relationship in both cases.
As far as the unit being able to accuratly measure the pressure, who cares. You know whats safe. As long as it's consistant you can see the relationship btwn the FI and standard ignition.
You might consider running a set with the same amount of powder (even if it is a low load) to see if there is a pressure difference and what it is. you may need to move the measuring divice a little around on the barrel because if front ignition works then the location of max pressure will change.
Linear Mode
