Pressure issues

[Topwater]

I weighed 15 brass of each to get an average weight in grains. I used my Gem Pro 250, that appears to have accuracy of 0.05 gr.

Winchester - 157.3031 gr.
Remington- 165.44 gr.
Lapua- 177.3708 gr.

This quite a bit bigger difference than anticipated. I have yet to measure the volume with alcohol. I’m not sure that my scale is fine enough to determine variations in weight of the alcohol. Is weighing the wrong process, should I just use a measured medicine dispensing cup? Need I be concerned with any evaporation during the process or is this a non issue?

 

[jlow]

Good job!

Your Gem Pro 250 is as sensitive as the expensive scales - it can detect differences of 0.02 grains.

The key to getting good data is to:
1) Use rubbing alcohol.
2) Make sure the cases have a spent primer in them
3) Put them on the scale and zero the scale.
4) Corse fill the case with a squeeze bottle.
5) Fine fill the case with a small 1 mL tuberculin syringe.
6) To make sure you get consistent and correct fills. Put the case between you and a small desk lamp.
7) Use a head mounted magnifier to look at the mouth of the case at an angle. You should be able to see a reflection of the light on the surface of the alcohol.
8) Fill the case slowly with the syringe until you get a flat meniscus. You know this happens when the reflection of the light gets bigger and disappears. Think of the meniscus as a mirror. When you are getting there it is a concave mirror. When you over fill it is a convex mirror. You are shooting for a flat mirror.
9) Take the case out carefully so that nothing spills.
10) put it on the scale and record the weight.
11) If you want volume in mL, you will need to adjust for the slightly less dense character of alcohol. But this is really unimportant unless you are interested in using the values in Quickload.

At least for you, you are just trying to show to yourself that the volumes are different between the different types of brass. They are of course different but perhaps you want to proof this to yourself which is OK.

Don't worry about evaporation.

Have you measured the overall length of your cases to make sure they are under SAAMI limit which for 243 Win is 2.045"?

 

[Topwater]

Thanks , jlow. Great instructions, concise and entirely clear. I need to check the oal of all the brass. If there are differences I will trim each to the SAAMI specs.

The quest for answers continues.

I was asked, “what is your end goal with this benchrest effort” ? I had to give it some thought. My goal is to have all pertinent ballistic information, read the wind correctly, and shoot a moa with the first shot at 1000 yds. If I can accomplish that at my age I’ll be quite pleased.