How do I read a .223 headspace gage?


TGT Addict
Dec 28, 2012
Cedar Park
So I got my dillon headspacing gage in today but I'm trying to figure out how to tell for sure when a case is below the bottom step, it's a bit hard to tell with the bevel around the head of the case if it's just barely below spec. Should I only toss the brass that is very obviously below that or is even a thousandth or two of excess headspace bad?


TGT Addict
May 11, 2009
H-Town, TX
Haven't used nor seen one, but from what I gather after an interwebs search, as long as its between the two steps you're fine.

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Active Member
Feb 17, 2013
Rusk County
The Dillon case gauge we have is supposed to be flush on both ends. You may need a small base die to get the head where it's supposed to be. Filing/trimming the mouth is the way to shorten the OAL.


Active Member
Jan 9, 2009
Round Rock
This is sized brass? If it drops that far into the gauge, you have set the shoulder back too far. Trash the brass? Probably not. A hair too much headspace will correct upon firing. Too much, it won't chamber.


TGT Addict
Dec 28, 2012
Cedar Park
Just wanted to add that I figured out how to accurately read the gage instead of just eyeball and feel it. Whooped out my 10X loupe and can very clearly tell when headspace is too long or too short. This is helping me get a good feel for being able to go by feel alone on the gage as well so eventually I hope I won't need it (although I'll probably be paranoid about it for a while).


TGT Addict
TGT Supporter
Apr 15, 2013
forget the Dillon case gauge as far as measuring headspace. IMHO they are only good for making sure you are fully sizing your case and case length

As far as really measuring headspace and knowing and not guessing you need to get the Hornady Headspace Kit.
This kit uses a jig with your dial calipers and you can measure the difference between a fired case from your gun and a resized case you just ran.
Now you can know for sure that you are loading ammo that will cycle in your gun

Hornady Manufacturing Company :: Reloading :: Metallic Reloading :: Tools & Gauges :: Lock-N-Load Gauges-Formerly Stoney Point :: Headspace Gauges :: Headspace Gauge Kits

I love Dillon products and I run a 650, but to me the Hornady Headspace kit is way more useful
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Been Called "Flash" Since I Was A Kid!
Jul 11, 2009
East Houston
I'm not familiar with your gauge but have had some experience with other headspace gauges. There are actually three gauges in a set. The gauges are "GO", "NO GO" and "FIELD GAUGE" You check your rifle with these

The bolt should close on a "GO" gauge. It should NOT close on a "NO GO". If it does close on the "NO GO" there is excessive headspace. The field gauge .....I'm not sure. I believe that the bolt should operate normally on a "FIELD" gauge.

I use cartridge standard gauges for my reloaded cartridges. If the loaded round will enter the gauge easily, slide out of the gauge without binding and not extend past the gauge surfaces, The thing will fire properly. I use these constantly.

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Active Member
Oct 20, 2011
The Dillon case gage is exactly what you need to ensure that your brass will chamber any any spec chamber. Good investment, now using it simple. Let's define terms. Base of the gage, where the two levels are defined by the milling, top of the gage is where the case mouth comes out. Upper ledge, the unmilled part of the base of the gage, lower ledge the milled portion of the base of the gage.

When you size the case, you want the base of the cartridge to sit in between the upper and lower ledges of the gage. The easiest way to do that is to use one of the greatest measurement devices ever designed, your finger. Your finger can feel differences in height of a few thousandths, which is fine for this operation.

Size the case until when inserted it is level with the top ledge. How can you tell, simple, run your finger from the outside of the gage over the case starting on the upper ledge. If it feels smooth, it is level, if it feels like you hit a bump up, lower the size die, and if it feels like your finger drops down, you are no longer flush. Again, if it feels smooth transitioning from ledge to cartridge case, it is level.

Then slowly adjust the die down until when you run your finger from the lower ledge and feel just a step up or level with the cartridge. Run that case back into the sizing die and then lock the ring. Run 5 or 6 more cases, check for consistency and adjust so that as many as possible are level, slightly over and under are fine. That sets your case right at the maximum spec for headspace (i.e. shoulder pushed back, smaller length from breech face to datum in this case). That round should chamber in any rifle.

If you are using Dillon dies, you already have a SB die, they cut them to minimum cartridge specs not chamber specs. You'll know you have a base issue if you flip the case and insert it backwards into the die. Rim and base issues will bind the casing. Lastly, once you have the brass sized properly, then use the other end to see if you need to trim. If the case mouth is sticking out, trim it flush.


Jan 15, 2014
N. Houston
I shoot for the middle myself on the length side i always refer to the book for the "trim to length". I reload in batchs of 200 so i set my die ( for the first time) sizing one then check with case gauge till i get its in the middle. Then set up my trimer and run all the pieces threw. I dont even try and presort for trimming anymore. It waste time and doing them all at the same time helps with consistency
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