Need HELP with rcbs precision mic and new bag of shellcases.

[hc1]

Thought i new how to use the rcbs gauge? Tell me if this is right.
Go to the range and shoot my remington 700 with winchester factory loads. Take the once fired cases and place one in the gauge and screw the headspace nut down untill it lightly touches the case. Measurment reads 0.001 - 0.002 past zero which comes to 2.1233, zero represents 2.1253 a mimimum number for 7mm remington mag, max being 2.1353. Set my full lenght sizer die (LEE) to resize if the headspace is longer than 2.1233.
With my once fired and many times fired cases there's no problem, except there where 2 cases that where too long and could not get them to resize, don't understand that.
The other problem is i ordered a bag of winchester shell cases from midway usa and check 3 of them with the mic gauge and all 3 of them measure 0.0180 below the mimimum or 2.1063. Whats up with that, am i correct in thinking the new cases have too short of a headspace measurement to load them and shoot,em?
On the RCBS precision from zero if the nut is screwed in, is to indicate a shorter headspace measurment, right ???

 

[rg1]

Not familiar with your measuring technique so your numbers I don't understand unless your measuring the outside overall length of your Mic with micrometers or is the numbers from a chart included with the Mic?
The Precision Mic may or may not be "exactly" calibrated for saami "zero". It will be very close but zero may be plus or minus a thousandth or two. It is basically a comparator to compare cases fired in your chamber and for setting your sizing die to only push the shoulder back a certain amount. Make sure fired cases don't have nicks on the case head or bent rims before measuring. You can find a few cases that spring back a little more than normal or cases that you have to screw the die in a little deeper in your press. New unfired cases should read zero on your mics dial. I have 3 Precision Mics and new factory loaded rounds I've measured read zero on two mics but one caliber Mic reads zero minus one or it turns past zero one hash mark. You might try sizing your new Win brass to see if that changes your shoulder measurement.
Here's a good article on the RCBS Precision Mic:
http://www.realguns.com/archives/035.htm
Here's another good article using Hornady's tool:
http://www.inlandshooters.net/index.php?contentid=99

 

[USSR]

...i ordered a bag of winchester shell cases from midway usa and check 3 of them with the mic gauge and all 3 of them measure 0.0180 below the mimimum or 2.1063. Whats up with that, am i correct in thinking the new cases have too short of a headspace measurement to load them and shoot,em?

hc1,

New unfired brass comes from the factory somewhat undersized, so as to fit any chamber. This is why it is a waste of time to FL size new brass, unless you want to open up the neck a bit more, which is a good idea. Shoot them as they are, but when you resize them, don't push the shoulder back as far as they were originally.

Don

 

[Ol` Joe]

Saami spec has a tolerance to it, usually ~ 0.010" with the plus being more then the minus. (example a datum lenght of 2.020" with a (+ 0.006") 2.026" and a (-0.004") 2.016" lenght being within spec.

The 30-06 SAAMI drawings I have show the `06 as having a headspace of 2.0487" min and 2.0587 max. Cartridge headspace lenght between these numbers, a difference of 0.010" will be exceptable to SAAMI.
Factory brass is almost always on the minus side to insure it fits in a tight chamber and most factory chambers are a little on the plus side for the same reason. The best fit for your rifle is to not move the shoulder at all, but to keep it at the lenght it came out after fire forming or reduce it no more then ~0.002" from there.

 

[hc1]

Thanks for the reply's.
For the RCBS mic gauge adjustment clarification. Let's say i insert a case in the gauge and screw the gauge nut down on the case. Now let's say the zero's line up before the nut touches the case,any marks past zero in a clockwise turn will be (-) negative readings, which will be a shorter headspace lenght. Touching the case with the nut before the zero's line up will be (+) measurments. If in fact my headspace lenght is as in my first post above. If i have a (+) measurment reading, then i would need to fl resize to a (-) smaller lenght of 0.001 ~ 0.002 below the measurment of a once fired case from my rifle?
Am I on the right track or did I derail.

 

[Walkalong]

Its best use is to get a good measurement from your chamber so you can size it just enough to fit your chamber.

If you want to size to SAMMI min or max, get a case gauge as well.

 

[USSR]

~ 0.002 below the measurment of a once fired case from my rifle?
Am I on the right track or did I derail.

That gets you where you want to be.

Don