Anyone with knowledge with RCBS headspace mic

GGibbs · July 15, 2013, 06:00 PM

Anyone here able to help me with the RCBS Precision Mic for figuring headspace to set full length die?
Thanks in advance.

mehavey · July 15, 2013, 08:25 PM

Measure a fired case (that still fits back in the chamber/bolt closes) with the RCBS mic.
That measurement is your 'baseline' for future sizing.

GGibbs · July 15, 2013, 09:08 PM

Yes sir, I understand that part....the example the instructions give is .006 headspace, it says size it down, take two off that, down to.004..my average headspace is -.001.... I am using RCBS FL Die, and it will only make the number go higher.back to zero,+.001,+.002 and so on.Instructions say take off .001-.002...my die wont lower the number only raise it.so it looks like I am making.
Beginning to think I should have never messed with it.lol

Bart B. · July 16, 2013, 09:14 AM

RCBS' instructions are sometimes weak in their understandability by us humans.

What they are talking about, is if your Mic reads +.006 over the zero mark on a fired case, that case headspace (which is typically .001" less than actual chamber headspace) is .006" longer than the SAAMI minimum standard of 2.0487" or 2.0547". But it's a bit less than the SAAMI maximum standard of 2.0587". That rifle's chamber headspace of about 2.0547" is in the middle of SAAMI specs and is just fine.

Their instructions say to set your full length sizing die in the press so after the case is sized, its headspace is .002" shorter than its fired position. If your fired cases measure -.001", your chamber headspace would then be 2.0487". That's about as perfect as one should expect. So adjust the die so the fired case shoulder is set back .002" past that and the mic should then read -.003".

GGibbs · July 16, 2013, 09:53 AM

Thanks Bart....That's what I thought it was trying to tell me. My issue is I start out with the die just touching the casing, the farther I screw the die in the number keeps going up, from,.001 to back to zero, then +001,+002,+.003 and so on, I can't get the number to go down.I thought I might be reading the mic backwards, I don't know whats happening.
Thanks man.

higgite · July 16, 2013, 09:59 AM

Quote:

Originally Posted by GGibbs

Thanks Bart....That's what I thought it was trying to tell me. My issue is I start out with the die just touching the casing, the farther I screw the die in the number keeps going up, from,.001 to back to zero, then +001,+002,+.003 and so on, I can't get the number to go down.I thought I might be reading the mic backwards, I don't know whats happening.
Thanks man.

Read Steve4102's explanation, post #4, in this thread. http://thefiringline.com/forums/showthread.php?t=528944

GGibbs · July 16, 2013, 06:33 PM

I finally got it set......my die is touching the shell plate very lightly, but I had to to get it, doesn't seem to affect anything.
Thanks for the help everyone.

wncchester · July 18, 2013, 08:25 PM

Everything a reloader does should be aimed at obtaining the results he needs, not at following some paper instruction sheet to the letter. Use your RCBS Mic gage the way Mehavey said.

July 15, 2013, 06:00 PM	#1
GGibbs Junior Member Join Date: July 3, 2013 Location: Southern Illinois Posts: 4	Anyone with knowledge with RCBS headspace mic Anyone here able to help me with the RCBS Precision Mic for figuring headspace to set full length die? Thanks in advance.

July 15, 2013, 08:25 PM	#2
mehavey Senior Member Join Date: June 17, 2010 Location: Virginia Posts: 6,896	Measure a fired case (that still fits back in the chamber/bolt closes) with the RCBS mic. That measurement is your 'baseline' for future sizing.

July 15, 2013, 09:08 PM	#3
GGibbs Junior Member Join Date: July 3, 2013 Location: Southern Illinois Posts: 4	Yes sir, I understand that part....the example the instructions give is .006 headspace, it says size it down, take two off that, down to.004..my average headspace is -.001.... I am using RCBS FL Die, and it will only make the number go higher.back to zero,+.001,+.002 and so on.Instructions say take off .001-.002...my die wont lower the number only raise it.so it looks like I am making. Beginning to think I should have never messed with it.lol

July 16, 2013, 09:14 AM	#4
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	RCBS' instructions are sometimes weak in their understandability by us humans. What they are talking about, is if your Mic reads +.006 over the zero mark on a fired case, that case headspace (which is typically .001" less than actual chamber headspace) is .006" longer than the SAAMI minimum standard of 2.0487" or 2.0547". But it's a bit less than the SAAMI maximum standard of 2.0587". That rifle's chamber headspace of about 2.0547" is in the middle of SAAMI specs and is just fine. Their instructions say to set your full length sizing die in the press so after the case is sized, its headspace is .002" shorter than its fired position. If your fired cases measure -.001", your chamber headspace would then be 2.0487". That's about as perfect as one should expect. So adjust the die so the fired case shoulder is set back .002" past that and the mic should then read -.003". Last edited by Bart B.; July 16, 2013 at 09:21 AM.

July 16, 2013, 09:53 AM	#5
GGibbs Junior Member Join Date: July 3, 2013 Location: Southern Illinois Posts: 4	Thanks Bart....That's what I thought it was trying to tell me. My issue is I start out with the die just touching the casing, the farther I screw the die in the number keeps going up, from,.001 to back to zero, then +001,+002,+.003 and so on, I can't get the number to go down.I thought I might be reading the mic backwards, I don't know whats happening. Thanks man.

July 16, 2013, 06:33 PM	#7
GGibbs Junior Member Join Date: July 3, 2013 Location: Southern Illinois Posts: 4	I finally got it set......my die is touching the shell plate very lightly, but I had to to get it, doesn't seem to affect anything. Thanks for the help everyone.

July 18, 2013, 08:25 PM	#8
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	Everything a reloader does should be aimed at obtaining the results he needs, not at following some paper instruction sheet to the letter. Use your RCBS Mic gage the way Mehavey said.