paul223 said:
Jlow,
What type of water should be used - good old mineralized water ?
Also at what temperature should this process be done?
I have not done this before but I will tell you what I would do if I was running the expriment.
First, I would just use tap water since that is what you normally clean your brass with if you were using SS media so it is good enough. Some people use distill water as that has minimal minerals in it and so its volume can be directly correlated to weight i.e. 1 mL of water = 1 gram. I personally think this is unimportant as you will have to include an additive (see below) and so this will blow the pure water idea anyway. The other reason is for the purpose we are dealing with, what is important is not so much the real volume of the case but their relative volume.
What I mean here is if you do what bheadboy suggested, i.e. just check 100 case and cull the outliers, is it really important? What I would do is to take 100 cases, number them, put each one on an electronic scale, zero the scale with the case on it, fill it with water until the surface is flat (this is the tricky part), record it with their number and go to the next one. Once you are done, you take those numbers, sort it in Excel and hopefully you will see a few outliers on both ends i.e. smallest and largest volume. Once you get that number, you will know what to do next. For example, if most are the same volume but there are a few small and large, just discard those or use them for foulers.
The key for this to work is to add in something to the water that decreases its surface tension so that you don’t get that meniscus which in this case would be like a dome at the case mouth. The problem with this is it is kind of like a balloon which can be inflated to different degree which will give you a lot of noise in your data. You can use something like isopropyl alcohol as suggested by dmoran and that should give you a flat surface across the top of the case. The key here is to know how much to add and how stable this mixture is. What I mean is you have to add enough so that you get that flat water surface at the neck opening and you will need to wear something like a magnifier to make sure it is as flat and as reproducibly as possible. Avoid adding more alcohol as necessary as the stuff tends to evaporate (see below). It is also important to be reproducible when you get that flat surface across the neck, any amount over the flat line or under the flat line will be “noise†in your data which affects reproducibility.
The other variable here is evaporation. Alcohol in general will tend to evaporate faster than water and so the stuff in the case or that batch that you made to use in the 100 cases will change over time and since alcohol has a different density than water, the density or weight per volume will change and that will screw the whole experiment up. To avoid this, one thing you can do is to sit the big batch on ice to chill it so that the evaporation is minimized. You can also check how fast the stuff evaporate off the case once you put the water/alcohol mixture into it over time by weighing it over and over again. Avoid chiling the brass especially if you are working in a humid enviroment as moisture will condense from the air on the brass on its ouside and this will really screw things up.
I know this sounds complicated but that is the nature of the beast when it comes to experimental procedures. The more OCD you are the better the data.
