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Dillon Case Gauge

We (Bob, my shooting buddy and myself) were working up some .223 reloads for our semi-auto rifles.  Bob's Bushmaster and my Saiga were the intended recipients for the reloads.  Bob had picked up some surplus powder from a local gun store and after I got the reloading info for it, I decided to put a couple of half boxes of ammo together (one for each of us) for the first round of testing at the range. 

At the range, I set up my PACT chronograph and ran 25 rounds over the skyscreens with satisfactory results.  For the first round of reloads using the 2230-S powder that Bob had picked up, they functioned flawlessly in my Saiga .223.  These were the first reloads I had put through it.  Up until now, my .223 reloading had been restricted to my Remington 788 bolt action rifle and a 14" Thompson Center Contender (I no longer have the T/C). 

When Bob got ready to try the reloads in his Bushmaster, it was a different story.  The bolt would not quite go into battery and the forward assist simply made it stick worse.  He had shot Federal factory rounds that functioned without problem....but the reloads were a different story.  I had never had this happen before and was a bit puzzled.  Time to do some research and also spend a little time with the dial calipers.

The dial calipers didn't yield much at all.  All of the loaded rounds, when checked against several factory rounds, were within .001" or there about.  I checked various dimensions on the cases, such as neck and base diameters, as well as the overall length of the cartridge.  The numbers looked good and a double check against OAL from my reloading manuals confirmed what I was finding with the dial calipers.  There had to be more.

After some research time on the internet, I realized that while my overall cartridge length was good, the dimension from the shoulder of the case to the case head was most likely just a little too long.  This is referred to as cartridge head space.

The .223 Remington case headspaces on the shoulder and if this length is a bit too long, your bolt will not lock up and go into battery.  Conversely, if you push the shoulder back a bit too much during the resizing step, you will have excessive headspace.  This causes the case to stretch (excessively during firing) and can result in case head separation.  When this happens, a lot of pressure is applied to the face of the bolt.  This can and has resulted in serious injury to the shooter when the action of the firearms fails as you pull the trigger.

Let's see how a cartridge case gauge can verify the problem and help you get the resizing die set up correctly.  After a trip to Dillon's retail outlet, I was ready to try the Dillon Case Gauge for my .223 reloads. 

The stainless steel Dillon case gauge is machined to the minimum SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) chamber specifications and maximum case length specifications.  If the reloaded cartridge fits into the case gauge correctly, you are assured that your reloads meet case dimension specs.


Here is a fired case from my Saiga .223 inserted into the case gauge.  Since this case has not been resized, it does not fit into the case gauge (remember the gauge is machined to the minimum SAAMI specs).  Nothing wrong here....this is the expected behavior given the case has been fired but not yet resized.


Here is a factory cartridge inserted into the case gauge.  The case gauge is machined with a high step and a low step.  The shoulder of the cartridge rests against the machined shoulder in the gauge.  If the resizing die has been adjusted properly, the base of the cartridge will rest somewhere between the low and high steps.  If this had been a resized case, and the base was higher than the high step, it means the resizing die needs to be adjusted down (screwed further into the press).  If the base was lower than the low step, it means the resizing die is adjusted down too far and needs to be backed out of the press a bit.  (Note:  A case that measures below the low step should be discarded.  The head space is considered excessive and the brass case could fail (case head separation) if reloaded and fired.)


The mouth of the case is checked at the opposite end of the case gauge.  After the resizing die has been adjusted so that the head space measurement is correct, drop the resized case into the case gauge.  If the mouth of the case is below the high step (as seen in the above photo), your case length is fine and requires no trimming.  If it extends above the high step, you need to trim the case using the method of your choice.


The Dillon case gauge is not designed to check the cartridge overall length dimension.  For that, I still use a dial caliper to check the reloaded cartridge after making adjustments to the bullet seating/crimp die on my press. 

So there you have it.  I hopefully have convinced you that the proper setup of your resizing die is very important as well as quite easy.  The few dollars invested in a case gauge (about $20) can easily pay for itself in the first box of ammo you reload by ensuring your cartridges chamber correctly. 




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