Home Forums Hunting & Shooting Ask The Gunwriters MD - RCBS Case Master Question

If memory serves you have complimented them before. My question is, are they accurate enough for culling out banana brass or is a ball micrometer necessary? Not a competitor here, varmints & game only.

Thanks in advance.

What I (and some others) have found is that generally lop-sided necks also mean varying case-wall thickness--which is what causes "banana brass." I checked this with both the Casemaster and a ball micrometer, and it's pretty consistent.

All of which is why I generally don't use brass that has a high percentage of lop-sided necks.

Yes, I understand that, my question is: Will my Case Master measure necks sufficiently well to determine which ones to cull or do I need to buy a ball mic?

Thank you again.

Yes, the Casemaster will measure necks sufficiently well. Get the same results from it as any other neck-measuring device I've tried, and have tried several.

John,
Are you saying using the Case Master with the dial indicator will measure neck wall thickness as well as a ball mic will?

When I have tried it I got enough differences between the Case Master method of measuring wall thickness and my ball mic that I didn't trust the CM. I even swapped in my good Mitutoyo indicator that measures to the nearest .0001.

Those were my results, but I always make sure the case-necks are either run over a sizing-die expander ball and chamfered, or fired and chamfered, before using the Casemaster. The other thing I do is press lightly on the top of the Casemaster plunger while turning the case on the spindle.

Would also point out that the Casemaster system measures the overall thickness of the neck, not just one point like a ball-mike--which would obviously pick up little imperfections in the neck. Have yet to find those ultra-sensitive imperfections to make any difference in a rifle's accuracy, including my 6mm PPC benchrest rifle, which is capable of consistent sub-.2 inch 5-shot groups at 100 yards.

John, thank you very much. I'm finding this to be a very useful tool.

I've wondered about that. I attached a stop collar to the sleeve that slides up and down with the idea it would provide more weight and be more consistent than pressing down with my finger.
I may try it again.

Casey,

Don't know how long it took me to figure out how much finger-pressure on the plunger resulted in the most consistent readings, but it was a while!

It also took a while to recognize that chamfering the case mouths also resulted in more consistency.

Note to self--remember to chamfer case necks first!

If I may step in, I find this topic very interesting as neck wall thickness consistency, in my opinion, can affect precision in competition. The RCBS is a versatile tool but I am questioning it’s accuracy.
First, as stated by someone above, if not enough weight is applied to the sleeve, the case may not be square with the gauge and give an inaccurate reading. I tried bringing down the gauge lower to use the spring tension inside the gauge a an extra weight to make sure the case is square with the gauge pin.
Second, you only get about 3/32 of the upper case measured as opposed to a ball micrometer where you can measure anywhere from the edge of the neck to the end of it close to the shoulder. RCBS should have designed it so you could measure the whole length of the neck. A thicker sliding sleeve could probably have done the job.
Just my opinion, Not perfect, may be wrong.