In the interests of sharing knowledge, I recently got a RCBS Prec Mic for all three of my rifles; 6MM Rem, .280 AI, and .375 H&H. Set the gage up for headspace then measured as carefully as my fumble fingers would allow the Winchester Supreme 140 gr Ballistic Silvertip factory round in .280 Rem before firing and the fully fireformed case after firing. Focused on recording the headspace difference between the two events. I found my cases grew about +.40 on initial firing in the improved chamber. Of course my end goal is to track and control how much I set back the shoulder on my first resizing. Stay tuned. (Also a small prayer for about +20 degrees temperature wouldn't hurt). Anyone have a favorable Precision Mic experience to bolster my confidence.

Don Boyd

Don,

I use the RCBS Precision Mic to measure "headspace" on a lot of my rifles.
Not only is it great for setting my FL dies, it also can tell me when FL sizing of fired cases is required, as opposed to neck sizing only.

I've even made "adaptors", for use with different cartridges.

Just keep good records, and they work well.

Kevin Gullette

Thanks Kevin, My primary interest in buying the Precision Mics was control of headspace during the resizing operation. I had a .257 Ack Imp that I sometimes caused head separations with by excessive resizing. I was following RCBS' rule of 'Bump the raised ram/shellholder with the FL die for factory look-a-like resizing'. When I also had a head separation on my .375 H&H (something like Elvis' Blue Suede Shoes) I decided to improve my measurement techniques -- the Precision Mic. Do you feel the Mic is telling us something useful? Is the bright shiny Mic cap in your picture one of the adaptors you made to fit other cartridges? Looks very professional. Can you give us your technique for the adaptor? Good job!

Don

I think they're an invaluable tool!
I set all my dies up to bump the shoulder .002", it gives me an instant reference point for all but my Weatherby cases, I still haven't worked out how to use them for my Weatherby's, but I'll get there eventually!

Without them I was prone to over-sizing my brass regularly, I used to neck size only, but you need to FL size after a few reloads anyway and I found it far better just to bump the shoulder .002" and not worry about neck sizing at all. I only use my neck dies on new brass to make the case mouths round now!
Cheers.

Don,

That is a special adaptor that I made for a 17AB and 17HeBee. My usual adaptors are cut-off caseheads....one for a 17PPC is in the box, at the top of the pic.

Although I use a lot of RCBS dies, I think that Redding has a better FL resizing instruction for a SPECIFIC chamber.

I chamber a fired case, with a stripped bolt(no firing pin assy, or spring loaded ejector), to check for tight or loose bolt handle closure. Remove the case and measure it's "headspace" with the precision mic. This gives a measureable number, versus a "feel" of bolt closure. After a few cases you gain data that tells you what is tight, and what is not.

Use of the mic while FL resizing shows how far the shoulder is being bumped. Remember that a die adjustment of only 1/32 of a turn, will result in a change of 0.0022".

Hope this helps.

Kevin Gullette

quote:

a die adjustment of only 1/32 of a turn, will result in a change of 0.0022".

Few reloaders seem to understand that. When I read some guy suggesting someone make sizer adjustments in "small increments" of a quarter turn (18 thou) I 'bout choke! The full range of most rifle cartridge headspace, min to max, is typically less than half that much.

I really like my RCBS Precision Case Mics (at least the case and loaded round thimble parts) but the Hornady case length and seating length tools plus a dial caliper works as well and is less costly for multipul cartridges.

I like the RCBS PM too. However, they do not make it for all the cartridges I shoot. For the "odd" ones I use the Redding Instant Indicator, which works well, also. Those people with Forster Co-ax presses will notice right off that the instant indicator will not work on it. I called Redding and their less than helpful solution was "get a different press."
My solution, which has worked well on 6mmBR, 22BR and 30BR rem cases, is to remove the spring from the indicator and use it on a known flat level surface.

I have an RCBS Precision Mic that I use for my 375H&H. I enjoy using the tool on my fired cases so I can be sure I'm not setting the case shoulder back more than two thousands of an inch.

I always wondered why RCBS would build the tool to measure the cartridge case using ANSI specs instead of SAAMI specs?
I thought SAAMI was the ruling body for firearm and ammo specs.

To All, I am so glad to read of all your experiences with the RCBS PM. Appreciate much your sharing with the forum. Initially I was somewhat intimidated with the instructions for the Mic but finally decided that the most important reading was the change between fully fireformed to my chamber and same reading after resizing. I'm also very glad to see some of you rely on +.002-.003 for shoulder setback. Previously, I found it so easy to resize too much. I think this little gadget will keep me inline. Again, thanks to all for sharing.

Don

I have one for my 338WMs and just bought another one for my new 30-06. I primarily use them for determining where the lands begin in my barrel so I can establish the optimum seating depth during load development.

The one for the 338 WMs has worked like a charm. The one for my 06 has not. I can't get it to give me an accurate reading and my rifle will not extract or eject the mock cartridge. I'll be buying a Hornady OAL gauge formerly made by Stoney Point...hopefully it will work better for that purpose. I agree with the other posters, the precision mic is a good product for measuring case shoulder setback.

quote:

ANSI specs instead of SAAMI

ANSI is the new SAAMI. I think.

quote:

ANSI is the new SAAMI. I think.

American National Standards institute

I'm betting that it's not at all related to SAAMI
Sporting Arms and Ammunition Manufacturers institute

quote:

Originally posted by vapodog:
American National Standards Institute

I'm betting that it's not at all related to SAAMI
Sporting Arms and Ammunition Manufacturers Institute

May have been around a couple of years longer, too.

In response to amamnn above: "I like the RCBS PM too. However, they do not make it for all the cartridges I shoot."
FWIW, I'm using a PM in .280 Rem caliber on a .280 Rem AI chambered in P.O. Ackely's shop when Mr. Ackley was still there as a "semi-retired advisor" to Mr. Dennis Bellm, for "headspace" measurement. At present I'm using factory rounds fired in my rifle for the initial "benchmark" measurement. I don't know about headspace but Winchester Supreme factory ammo gives a very full fireformed case. The PM reads 30.1 thru 31.0 on 'as-fired' cases. Next will be setting up the Redding FL sizing die for -.002" - -.003" then off for action tuning/smoothing (Pre-64-70). Again thanks to all.

Don Boyd

That's very nice, Don, but--huh?

In response to the ANSI SAAMI question--they are not exactly the same folks but they do co-operate. Anyone who actually buys SAAMI publications will notice the "ANSI/SAAMI" logo on publications like:

"Voluntary Performance Standards for Pressure and Velocity of Centerfire Rifle Sporting Ammunition for the Use of Commercial Manufacturers" and other classics. Admittedly, their choice of titles leaves something to be desired if it were a best seller.

quote:

Originally posted by sep:
I can't get it to give me an accurate reading and my rifle will not extract or eject the mock cartridge.

I'm with you sep! The so-called "freebore tool" is a waste of time.

But I LOVE the RCBS precision mic otherwise!

I measure the ogives of ammo that shoot accurately with the land/ogive nut and then use DUMMY rounds with Prussian Blue on the bullet and slowly seat farther out to determine actual length to contact with lands.

This will give you a more accurate ogive readings than most comparators.

Amamnn, My apologies. My intent was to highlight that it was possible in some instances for more than one cartridge in the same caliber to fit the same Prec Mic. Please forgive a senior moment!