Which is better to measure headspace?


November 14, 2010, 01:16 AM
I want a tool to measure the correct amount of FL sizing and was looking at buying either a RCBS Precision Mic, or a Hornady Lock-N-Load Headspace Gage. Which is better in your opinion, and why? Thanks-

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Steve Marshall
November 14, 2010, 08:03 AM
I'll give you another option. Case gages. Mine are all from Wilson but there are others out there. With a drop indicator or even a caliper you can easily measure cartridge headspace. I've never had a case that measured properly in a case gage fail to fit a rifle. Should you decide to go with what you asked about, you'll need some sort of calibration unit such as a headspace gage. There have been far too many reports of case-mics etc. being out of calibration.

November 14, 2010, 08:23 AM
I prefer the Hornady as it's quicker to use than the RCBS. With a decent caliper they also let you determine and keep track of the shoulder bump specifically for your chamber. The Wilson drop in gauges assure safe ammo while the Hornady (or RCBS mic) allow safe ammo with less overworking of the brass.

November 14, 2010, 09:37 AM
For the RCBS Precision Mic, Hornady L-N-L, Sinclair Bump gauge or others, the calibration unit is a set of fired cases from your rifle. You measured the fired cases to get an average figure then set your resizing die to move the shoulder back the desired amount.

Two to three thousands for bolt rifles, three to five for semi-autos or something along those lines. See the instructions for what the tool's manufacturer recommends.

This process will minimize the working of the brass on resizing and should extend case life.

These cases may or may not fit in other rifles since the resizing is tailored to a specific chamber

The drop in gauges measure the headspace to the spec for that cartridge. Cases gauged in a drop in gauge should fit any rifle with a chamber cut to spec.

Note, bottle neck cartridge case gauges measure only shoulder position and over all case length. They are not a chamber gauge like the hand gun cartridge equivalent. So, a case could fit into a case gauge but not fit your chamber. Read the full description on the case gauges from the manufacturer's sites.

If you are loading for one rifle or segregate your brass, I would get the RCBS, Hornady, or Sinclair style gauges.

November 14, 2010, 12:13 PM
I actually prefer the RCBS Precision Mic mainly from being a part-time machinist for nearly 37 years. I just prefer the micrometer type marked dial of the Mic. It does take several turns of the dial to screw the dial in to touch the shoulder of the case. The Hornady tool mounted to calipers can just slide into contact. The RCBS tool is expensive, the bullet length measuring tool part of the Mic set is tedious to use but will work after much trial and tinkering. The Hornady set will measure most all calibers and if you want to check several different calibers, then the Hornady set will do the job and be much cheaper than buying several RCBS Mics. I have a RCBS Precision Mic for .223 and 30-06 (also measures my 25-06 as the cases are the same) but also bought the Hornady set. Both will accomplish your goals of setting your sizing dies to only push the shoulder back a measured amount. Highly recommended to extend the life of your cases PLUS will help prevent case separations, a big safety concern.
Have you seen these write-ups?

November 14, 2010, 12:32 PM
I've got by pretty darn good for 50 years using a .5 cent birthday candle.

Strip the bolt, smoke the case with the candle, and keep adjusting the die down until the headspace shoulder in the chamber takes the soot off the case shoulder.

Carried one step further, you can "feel" the bolt close on the case, and when just very slight resistance is felt, headspace is perfect.


November 14, 2010, 03:53 PM
RC -
Just wondering: Do you get to make a wish when you blow out the candle?


November 14, 2010, 04:21 PM
I've used the RCBS Precision Mic for years, and been very happy with it. Have never used the Hornady, so cannot compare them.


November 14, 2010, 04:35 PM
I have several RCBS Mics and the Stoney Point tools (Hornady). Effectively they are equal in use but I prefer the Mics because they are repeatable from session to session and I keep relivant measurements in the die box but I no longer bother with their silly "freebore" dummy cartridge for finding max OAL. I find my caliper mounted tools frequently read a bit different at each session so they require starting over each time. But, for multipul cartridges, the Hornady sets are MUCH less costly than a pile of Mics and all reloaders need a precision caliper anyway!

Also have a couple of Wilson cartridge gages. They are great for insuring the reloaded ammo meets SAMMI spec for all rifles ever made for a given cartridge. But, I custom make my ammo for MY rifles, not everyone else's. Meeting factory specs are of almost no interest to me so I rarely use them, and then only if I'm loading for someone else.

I NEVER take an "average" of anything when using my case gages. The longest (head-to-shoulder) length of a batch of cases is somewhat smaller than the chamber they are fired in so I FL size my cases so the longest FL sized lenght case is equal to the longest fired case length; everything works fine. If I used an average length figure I would be overworking the longest cases for no valid reason and having a tad more "head space" slop than is absolutely necessary.

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