Precision Mic Help

[Mr Blu]

Hey y'all.

I've done some searching here, as well as on YouTube, and I have an idea on how to use the RCBS Precision Mic. I just want to confirm my findings.


Steps to follow to shoulder bump brass for resizing/reloading.

1) Get an average measurement of once fired brass. (Example : -3.5 tick marks on mic)

2) Subtract 2. (Example : -3.5 - 2 = -1.5)

3) Resize brass to the remainder.




I have been chewing on this for a while and I'm afraid that I've simply thought too hard about it. It's a very simple tool and it cannot be as hard as I think it is.

[Flyin Brian]

Yeah that's pretty much how it works. I don't use the RCBS, I use the Sinclair Comparator kit which does the same thing but works on most all calibers:

http://www.sinclairintl.com/reloading-equipment/measuring-tools/bullet-comparator-inserts/sinclair-insert-style-bullet-comparator-prod34014.aspx

It sure saves on brass life when you are only bumping the shoulder .002"

[rg1]

Sounds like you're on the right track. A rule of thumb some go by is to bump the shoulder back 1 to 2 thousandths for a bolt action and 3-4 for a semi-auto or lever action. I've measured a few factory rounds and find that they measure minus 1 on my Mic. You need to measure several fired cases to find how much the shoulders expand forward and measure several to see what you're sizing them to. If you're shooting for 2 thousandths make sure the longest ones come out at minus 2 with some possibly minus 3 or so from the fired dimension. The fired cases spring back some so your chamber could be slightly longer. The Precision Mic is a great tool for adjusting your sizing dies. It really is nice for rifles with near maximum headspace that the shoulders of new brass expand forward maybe 6-8 thousandths and you don't want to push them back to zero. Like Flyin Brian mentioned, it will increase the life of your brass and will definitely increase the safety of your reloads by helping prevent case separations.

[Mr Blu]

Thanks.

I hate the feeling of not knowing how to use a tool, when said tool is actually very simple.

[Roach]

Hey y'all.

I've done some searching here, as well as on YouTube, and I have an idea on how to use the RCBS Precision Mic. I just want to confirm my findings.


Steps to follow to shoulder bump brass for resizing/reloading.

1) Get an average measurement of once fired brass. (Example : -3.5 tick marks on mic)

2) Subtract 2. (Example : -3.5 - 2 = -1.5)

3) Resize brass to the remainder.




I have been chewing on this for a while and I'm afraid that I've simply thought too hard about it. It's a very simple tool and it cannot be as hard as I think it is.

Your math is a little off. If your fire formed brass is at -3.5 you want to bump the shoulder back to -5.5. One to two thousandths (BELOW) like others have said for a bolt gun.

[Mr Blu]

Your math is a little off. If your fire formed brass is at -3.5 you want to bump the shoulder back to -5.5. One to two thousandths (BELOW) like others have said for a bolt gun.

Dammit.

Thanks.

[FLIGHT762]

Here's a review of the RCBS mic with some photos that confirms what roach has explained how to use the gauge.

http://www.gunsumerreports.com/review_rcbs_precision_mic_308-win.php

I prefer the Hornady or the Sinclair gauges, but the RCBS will do what you want.