Go Back   CMP Forums > CMP General > Ask Each Other > Reloading
Register FAQ Members List Calendar Mark Forums Read

Reply
 
Thread Tools Display Modes
  #1  
Old 03-23-2010, 02:53 PM
drywash drywash is offline
 
Join Date: Oct 2009
Posts: 1,679
Default Learning to use RCBS Precision Mic.

Got a new RCBS 30-06 Precision micrometer. Only problem is it takes "three Philidelphia Lawers to dechipher and understand it's us. If someone can explain it's use in (simple) terms I am all ears.... Thanks. I am third on Midways backorder for Wilson. Thanks
Reply With Quote
  #2  
Old 03-24-2010, 08:02 AM
sirupate sirupate is offline
 
Join Date: Feb 2010
Location: Ohio
Posts: 46
Default

OK...I'm not at home to look at my Mic, but it has the capability to measure the length of your ammo as respects the bullet ogive versus the throat of your chamber where the lands begin. I pretty much ignore this feature and it is probably only useful for bolt action rifles where you want the bullet out touching the lands for accuracy purposes. This isn't a consideration for semi-autos, or where high reliability/function is important.

The other (more important) function of the Mic is to tell you the cartridge headspace of your brass versus the chamber headspace of your rifle. On the Mic, a measure of "0" means SAAMI minimum measurement. A measurement of "10" would be SAAMI max. If you have some commercial 30-06 ammo, insert a cartridge into the Mic and take a measurement. It should measure a bit less than "0". My Federal American Eagle 06 ammo measures minus 1...that is, 1/1000 of an inch less than SAAMI minimum. Some recent Winchester new brass measured between minus 3 and zero on my Mic.

When you size brass on your press, you want to size it down to about minus 1on your Mic. So, adjust your sizing die down gradually until you get that measurement. Doing this will help ensure reliable function and lower chance of slam-fire. You can also get a rough idea of your rifle's chamber headspace by measuring a small sample of brass fired from your rifle. Most military rifles do not have SAAMI minimum headspace so that function in combat environments is reliable. Let's say that your sample of fired brass measures a plus 7, or plus 8. That would indicate that your rifle's chamber is about 7 or 8thousandths over SAAMI minimum. Remember that SAAMI max is plus 10. Many sporting rifles will measure at SAAMI minimum unless they have seen extensive wear.

This is getting long already...see why the instruction sheet is long too? I've not gotten into the topic of slam-fires, or sizing brass for longer brass life. You really need to understand the concept of chamber headspace and how that relates to cartridge brass headspace and what happens when the two measurements are off by very much in either direction.

Jeff
Reply With Quote
  #3  
Old 03-24-2010, 08:34 AM
drywash drywash is offline
 
Join Date: Oct 2009
Posts: 1,679
Default

Thanks.also should tell me how to adjust die to get "Shoulder" set correctly. I will read long instruction sheet again and measure spent hxp/l.c. Should get hang of it. Rather expensive tool. Hate to "not use it".
Reply With Quote
  #4  
Old 03-24-2010, 08:50 AM
sirupate sirupate is offline
 
Join Date: Feb 2010
Location: Ohio
Posts: 46
Default

Quote:
Originally Posted by drywash View Post
Thanks.also should tell me how to adjust die to get "Shoulder" set correctly. I will read long instruction sheet again and measure spent hxp/l.c. Should get hang of it. Rather expensive tool. Hate to "not use it".
Usually your die manufacturer has instructions that say something like "turn sizing die down until contact with shellholder at full press handle stroke, then add 1/4 turn"...something like that. Not very precise, given that we are talking differences of 1/1000 of an inch. Instead, do most of that, but begin measuring the brass as you make 1/4 turns downward. When you get a few measurements of minus 1 (or so..could go to minus 2), your sizing die is set for that brass. The Precision Mic is just a more precise method of setting your sizing die. Also bear in mind that different brands of brass may size differently depending on hardness and thickness. I take periodic measurements for brass used in semi-autos just to be sure.

Jeff
Reply With Quote
  #5  
Old 03-24-2010, 08:33 PM
1hdrocks 1hdrocks is offline
 
Join Date: Oct 2009
Location: Illinois
Posts: 771
Default

I usually measure 10 factory rounds to see where they're at. I then shoot 10 rounds in my gun and measure them. I write them down and tabulate the score. 5 rds at 0, 3 rds at +1, 2 rds at +2. Looks like "most" rounds are at or near the "minimum". Well, I need to size so they will fit in the chamber but I don't want to size to 0 as that is the fired dimension. So in this case I would probably size to -2 or -3, possibly even -4. As mentioned there are differences in thickness and hardness. If you ever size your brass and it ain't enough, you'll know it, presto, rounds won't chamber and will be real fun getting out. Another reason to check as you go, before loading 500 rds that don't work. I am not advocating to oversize by any means. I've found that usually 2-3 under your rifles minimum works pretty good, some guys like the extra comfort of about 4 in a semi-auto. If you have several M1's that you want to be able to shoot all of your ammo in, shoot each rifle, measure brass for each one, load all rounds to the measurement of the "smallest" one. Probably left something out and made things clear as mud for ya'. Good luck.
Reply With Quote
  #6  
Old 03-25-2010, 08:12 AM
dcsafety dcsafety is offline
 
Join Date: Nov 2009
Location: Franklin, PA
Posts: 19
Default RCBS Precision Mic use

I use both the .223 and the .30-06 mic and am very happy with them. Yes it does take a while to get on to their proper use but it has taken my case prep to a whole new level. The advise to size your brass to just under SAAMI spec is I believe good advise unless you measure fired brass from your gun and see if you have a tight chamber or an oversize chamber.

Three of us have the exact same manufacture's AR and fired cases measure from just .002 to .008 over SAAMI specs, depending on the gun. Mine has the tightest chamber (.002) and I re-size to .002 under SAAMI specs for reliability. the others can get away with resizing to spec or just over. The importance I believe is consistency in your process. If all your cases are to the same size it only stands to reason velocities and accuracy will be more consistent.

It is surprising how much variation in re-sized brass there is after adjusting your die by following the manufacturer recommendations without using the Mic.

You can also use the mic to measure run out and set your bullet seating depth when using heavy bullets at the long line as well. Its a great tool.

This is only my take on it and how I use it. I am not the manufacturer of the product and I know the folks at RCBS will be glad to help you further.

Good luck
Semper Fi
Reply With Quote
  #7  
Old 03-24-2010, 08:43 AM
BruceR BruceR is offline
 
Join Date: Oct 2009
Location: Vermont
Posts: 340
Default

RCBS istruction sheets could be written better. The products are good, the written info not so much.
Reply With Quote
  #8  
Old 03-26-2010, 12:39 AM
Wes_VB Wes_VB is offline
 
Join Date: Oct 2009
Location: Colorado Springs
Posts: 286
Default

Every chamber is different. So you use the tool to determine a die setting that bumps the shoulder back about .002" from your fired average.
Take about five rounds that have been fired in the rifle you are reloading for.
Measure them with the tool. (Use the part with the big hole, the part with the small hole is used for loaded ogive length.) Once you establish an average write that number down. example .003"
Set your die up so it just barely touches the shell holder and lock it down. Resize a case and check it with the tool. If it is long Loosen the die and set it about an 1/8 of turn further down and run the case through again. Keep adjusting the die until you are resizing cases .002" under the measured average of fired cases. In this case .001" since your average was .003".
If you reload for a different rifle then you will have to establish a new average for the rifle and set the dies accordingly.
Seems tedious but if you have a long chamber it will definitely extend the life of your brass over resizing so you are bumping the shoulder more than .003" back from where the fired brass shoulder is. Once you have an average for a particular rifle write that number in your reloading book for reference when loading the next batch.
The other two pieces have several uses. The best one is being able to track throat wear. For my 308 F Classer I use it to load precise distances from the lands.
For the Garand and even the 03 ammo loaded out to the lands or even close will not fit in the magazine so it's useless for the milsurps.

Last edited by Wes_VB; 03-26-2010 at 12:42 AM.
Reply With Quote
  #9  
Old 03-26-2010, 08:07 AM
douglas34474 douglas34474 is offline
 
Join Date: Oct 2009
Location: Ocala, Florida
Posts: 1,352
Default

Quote:
Originally Posted by Wes_VB View Post
Set your die up so it just barely touches the shell holder and lock it down. Resize a case and check it with the tool. If it is long Loosen the die and set it about an 1/8 of turn further down and run the case through again. Keep adjusting the die until you are resizing cases .002" under the measured average of fired cases.
I have to ask; if you adjust your die so that it is touching the shell holder, how do you get your die to screw your die down another 1/8 turn past the shell holder?
Reply With Quote
  #10  
Old 03-26-2010, 09:07 AM
sirupate sirupate is offline
 
Join Date: Feb 2010
Location: Ohio
Posts: 46
Default

Quote:
Originally Posted by douglas34474 View Post
I have to ask; if you adjust your die so that it is touching the shell holder, how do you get your die to screw your die down another 1/8 turn past the shell holder?
Easy...just lift the press ram and adjust the die downward another 1/8th turn.
Or...was that sarcasm....couldn't tell.

Jeff
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 10:16 AM.