View Full Version : checking head space?

June 7, 2010, 08:47 PM
Hi folks.. Have a question.. Whats the best way to check head space without gauges? can I use a fired case? please explain..:confused:



T. O'Heir
June 7, 2010, 09:00 PM
A fired case tells you nothing. Neither does bits of tape, loaded factory cartridges or anything else.
Only headspace guages will tell you if the headspace is within tolerance. Headspace guages are precision instruments that measure nothing.

June 7, 2010, 09:11 PM
What kind of gun are you talking about?

Not saying I recommend this, but you can get a rough idea by putting masking tape on the head of an unfired case.

Another method I've used is to glue a brass rod into an unfired case so you can push and pull from the muzzle, notch the brass rod right at the muzzle with a razor blade so you can see how much it moves; also not a precision measuring device.

June 7, 2010, 09:12 PM
Head space gages are cheaper then rifles or eyeballs.

Jim Watson
June 7, 2010, 10:10 PM
The Internet has gotten more people worried about headspace than anything except the difference between clips and magazine.

Exactly what is your situation and why do you suspect you need to check your headspace?

June 8, 2010, 04:45 AM

June 8, 2010, 06:16 AM
Checkout Mike Bellm TC website...

Correct headspace is essential to accuracy, reliable functioning, and good case life. Here is how you measure it, make corrections, and also measure throat length.

Headspace is a very simple concept that is both easy to understand and easy to measure, especially in any break open gun like the TC Encore or Contender/G2. I'll show you how.

Too many barrels are given up on as unsatisfactory, or, worse, folks leave the TC system in despair simply because of headspace issues. Don't be one of them! The methods you get away with shooting bolt actions simply do not work with springy break open actions. The break open actions are different and must be handled differently.

Understanding headspace can literally save you hundreds of dollars, thousands of dollars if you are one who does a lot of barrel swapping in your quest for accuracy and the performance dreams are made of.

This is what it should be. .001" BETWEEN THE CASE HEAD AND THE BREECHFACE.

Note that the case shoulder is in contact with the chamber shoulder while there is space between the case rim and the bottom of the rim counterbore, indicating the case is "headspaced" or its forward movement stopped by the shoulder, not the rim, and that the actual space at the head, "headspace," is .001" less than whatever the barrel-to-frame gap actually measures.

June 8, 2010, 07:50 AM
IT is a Remington 600 in 6mm REM I found it at a auction but it didn't have a bolt. I found a bolt for it and I just thought I should check head space before I went about shooting it.. Since it is the only 6mm REM that I have and head space gauges are expensive I heard that you could check it with a fired case..

It closes just fine and smooth on an unfired round, but I thought I should check the head space because of the different bolt..

Thanks for the many replies.


Jim Watson
June 8, 2010, 08:29 AM
I think a replacement bolt is grounds for checking headspace.
If a round will chamber, then you are either ok or over on headspace, no need to worry about a Go gauge, a No-Go would be adequate.
Bear in mind that if the combination has excess headspace, getting it corrected will require setting the barrel back a turn and rechambering, which will run up your total cost a lot.

The other alternative would be to treat it like a wildcat. Assuming you can fire factory loads without a case head separation or a lot of stretch that would cause a separation the next time, the brass could be resized just enough to load back into the same gun, being careful not to set the shoulder back too far.

James K
June 8, 2010, 10:01 PM
Hi, ammo.crafter,

Just curious how you can say the distance between the case head and the breechface must be exactly .001" when cartridge tolerances allow a difference of greater than that between any two rounds of the same caliber.

With an absolute distance that is well under cartridge tolerances, won't some cartridges have more than that and/or others not chamber at all? Or will the gun be fired only with cartridges that are made to a zero tolerance?


June 8, 2010, 11:29 PM
You can get a NO-GO headspace gauge from this source -


...and head space gauges are expensive

I'm not sure what you mean by expensive, but a single gauge runs around $30 or so. This is right in there with driving around and taking it to a gunsmith to have headspace checked, IMO.

Instructions for using these gauges usually tell you to strip the bolt so you aren't fighting the ejector, insert the gauge in the chamber and then see if the bolt closes with light pressure on the handle. It should close on a GO gauge (or unfired factory ammo) easily and should not close on a NO-GO gauge.

As discussed above, if it closes on a NO-GO, you are looking at some expense to have the barrel shoulder turned down 1 thread and rechambered. However, considering the rarity of the Remington 600, this may be what you want. Make sure the gunsmith can deal with the front sight and rib... :)

June 9, 2010, 09:06 AM
Well I went ahead and rented some go, no go gauges and will check for safety... However I went ahead and braved a shot with some new factory ammo..NO Problems.. Checked the brass and did not see any signs of high or low pressure.. Brass looked clean with only a minor scratch on the side, no signs of swelling, looked fine.. The gauges should be here in a couple of days and I will check before I fire another round.. Thanks for all your feed back..You know back a few years ago I used to buy used guns at gun shows and never even thought of checking head space.. I fired them at the range and never had any problems... I guess I was lucky..:eek:


June 9, 2010, 12:07 PM

Hatcher intentionally increased headspace to something like 1/8" in the .30-06 and still didn't blow caseheads on the first firing. What you could have done was use a case comparator, like the RCBS Precision Mic or the one for the Hornady L-N-L gauge and measured the cases before and after. You can pretty well guess that if they didn't grow more than 0.008" that everything was in field go gauge spec.

BTW, if you find you need to have the headspace corrected, lap your lugs first (an accuracy step, but something easy and a good idea to do with a non-original bolt to assure the lugs fit properly), as the metal you take off will grow headspace.


As I expect you already know, but for the sake of others reading the thread: SAAMI specs can show maximum case lengths at the shoulder that are longer than minimum chamber dimensions. Because a chamber is wider than the maximum cartridge diameter, the bolt of a conventional rifle action is expected to be able to close on and squeeze the cartridge a little shorter and fatter to fit if needed.

The TC actions don't have the camming of a bolt locking lug or the leverage of a bolt handle to assist in closing on a long case. So in their case, as with NATO chambers, interference fit is not allowed. Insuring no interference is where that 0.001" gap for TC chambers comes from. Another factor may be that number of benchrest shooters say they find that bumping shoulders back 0.001" shorter than the chamber rather than strictly neck-only sizing, produces better accuracy.

So I expect one or both of the above considerations are at play in the statement regarding what headspace "should" be. But as with all things gun, YMMV. I would not, for example, run a gas gun chamber that tight. Too much chance of encouraging slamfires or getting feed jams.

June 9, 2010, 01:14 PM
You can rent headspace gauges from the same folks who rent reamers (4-D products, reamerrentals.com, etc)

June 9, 2010, 03:27 PM
FWIW: I have, on occasion, cut a .0015 feeler gauge the same size as the case head and placed it and a case into the bolt face and closed the bolt. With proper headspace the bolt should close with a bit of a 'crush' feel to it.
For accuracy I prefer a a '0' headspace. For hunting I want a case with headspace so the bolt is not sticky. In my many years of experimenting with this I personally feel headspace is not really critical, except with break-open guns such as the encore or contender.

June 9, 2010, 03:47 PM
A fired case tells you nothing. Neither does bits of tape, loaded factory cartridges or anything else.
Only headspace guages will tell you if the headspace is within tolerance. Headspace guages are precision instruments that measure nothing.

As for masking tape. It does represent a pretty good go-no go gage. Better than nothing. A highly respected rifle builder once told me to size my cases so that I could close the bolt "like nothing was there". One piece of masking tape placed on the case head should result in some feel. Two, lots of feel. Three, and the bolt should not close.

Not a precise way to measure head space, by any means, but a good way to keep you out of trouble if you don't have a gage.

I disagree that a fired case tells you nothing. It tells you everything you need to know, IF you have a way to compare it with other cases.

The RCBS Mic gage is very good, because it measures the difference between a fired case (perfect head space), and your sized cases. I find that .002 sometimes gives me a little too much "feel" when I close the bolt. .003 is about right. Because brass is elastic, not all of it gets sized (or stays sized) the same amount. You need to allow for that when you size. Hunting ammo, little or no feel. Varmint, target, it's up to you. My experience is with bolt action rifles.:cool:

June 10, 2010, 01:13 AM
The bit about break-open actions and headspace makes no sense. On occasion, I have made reamers for rimmed cases that I wanted really tight. You make them without the rim cutter section, and recess the rim area into the barrel first. Then you pick a brand of brass and resize it. This is your headspace gauge. If you want .001 tolerance on the rim you are still going to be picking through your brass because of the variation in manufactoring. I guess you could pick out the thinnest rim and face off the others, but I never heard of anyone doing it. It sounds like the only way to headspace your way is to custom make the brass like it was a wildcat? I don't know, you lost me there somewhere.

June 10, 2010, 09:49 AM
QUOTE from Nnobby45
The RCBS Mic gage is very good, because it measures the difference between a fired case (perfect head space), and your sized cases. I find that .002 sometimes gives me a little too much "feel" when I close the bolt. .003 is about right. Because brass is elastic, not all of it gets sized (or stays sized) the same amount. You need to allow for that when you size. Hunting ammo, little or no feel. Varmint, target, it's up to you. My experience is with bolt action rifles.
Yesterday 04:27 PM

End Quote

I agree with your post on bolt rifles.
For precision target type shooting, you want the headspace on the tighter side, on a hunting rifle, especially when hunting big game, a litle more headspace is a good thing.

Just be sure that you check the FP protrusion when going to a little more headspace.
It's never a bad idea to buy a set of HS guages for the calibers that you have or want to buy, especially when buying a weapon at a gun show or used.
As a retired gunsmith, I've seen too many blown up rifles from excessive headspace, some resulting in some pretty bad injuries.
I know that HS guages are not cheap, but can be sold without too much loss later.
Buy the same brand when getting go and no go.
Check E Bay, sometimes you can find some deals.

If it's just one rifle and you don't plan on ever buying more in that caliber, sometimes it's cheaper to just take it to a gunsmith.
Also, on some calibers, headspace guages work on more than one caliber, so check before buying for a spicific caliber.
Belted magnums take the same size HS guage. Except the .240 Weatherby Mag which is a different case size.
Most belted mags are based on the .375 H&H mag case. If not, it will need the correct guage to get the right reading.

If you can only afford one HS guage, get the NO GO. A new loaded round will close with a NO GO on a new unfired round.
You can always find out the difference in thousanths betwen the GO and NO GO and carry shims that are just a little over the difference in total length between the GO and No GO, put the shim pack on top of the NO GO guage. If the bolt closes on it, the headspace is too tight.
Go very easy on the bolt if trying this and be sure the rifle is pointed in a safe direction so that if it goes off, the round will not hit any one or fly into the air or take out your big screen TV, best to have the rifle pointed at the ground. Strip the bolt of the extractor, FP and ejector.
If the stripped bolt closes on a NO GO go, you know the HS is excessive, don't fire the weapon without geting it checked out by a qualified gunsmith.

I always checked with both guages just to cover my rear end.
When checking HS, always strip the bolt first and make sure that the chamber is clean.
On a weapon like a Mini 14, M1, AR, REM Browning, Win or others with a bolt that is not operated by a bolt handle (usually gas operated bolt), strip the gun and bolt. If the bolt fully closes on a NO GO, it has excessive HS and is unsafe to fire. Put the stripped bolt only into the weapon with the No Go HS guage. If the bolt won't fully close, then it's OK, again, clean the chamber first.

On a weapon like a semi auto Rem, Win or Browning that has a bolt that locks into spireled lugs, check the lugs for wear, you can feel them with your finger, just don't let the bolt snap closed on your finger, it really smarts. Ridges on the lugs in the receiver that are worn away or that you can feel groves in can mean an unsafe weapon or at least one that is starting to get some bad wear on it.

If if the locking ridges are worn away, and I have seen this more than once. Do not fire a weapon in that condition, have it checked by a gunsmith. People will try to unload these at gun shows, they are unafe.
Stripping the bolt or bolt and weapon is a pain in the butt, but it's the only way to get a true reading.

Never push down hard on a bolt when checking headspace. One finger without a lot of pressure should be all that is needed.
The camming action of a bolt gun is really strong, and if you force the bolt closed on a NO GO and the heaspace is ok, you can hurt the weapon.

Older weapons where the bolt almost fully closes tend to indicate that the headspace is getting near the max to for getting good accuracy and I would not fire hot loads in them. This may be OK on a big game rifle, but for most uses, it shows that you may have to re barrel for maximum accuracy. It is safe to fire as long as the bolt does not close.

There are field guages which show the max headspace. I don't like to shoot a weapon that will close on a NO GO, but won't on a field guage, especially if it almost closed on that guage.

On any semi auto that the bolt is hard to get to, so that you can check the headspace, put a mark on the bolt that exactly extends to the receiver and lines up perfect (you don't have to scratch it, just make sure it does not come off easy), then strip the bolt, clean the chamber , put the NO GO headspace guage into the weapon's chamber and re assemble except for the parts taken off the bolt (extractor, ejector and FP).
Re assemble the weapon, being careful not to erase the mark you put on it.
If the mark on the bolt is back to the rear from the mark on the receiver, your head space is ok. If the mark is still even, there is a excessive headspace, take the weaon to a good gunsnith to be checked.

Be sure to check and clean any bores on new, used and especially mil surp weapons before firing.
Sorry for the long post, many of you know this, but the newer shooters may not, and safety was always number 1 with me.

Best Regards, John K

June 10, 2010, 10:37 AM
In gunsmithing school, we were told to never close a break open on a headspace guage.

True or not, I took the info to heart. I think the instructor was just trying to be on the safe side. We had students who could break a ball bearing with a rubber mallet.

I found it was better to put a dummy round in the chamber and put tape on the top of the dummy round.

I would then close the action, open and check the tape.
If more there was needed, I added another piece until I saw an impression.
Knowing the approx thickness of the tape, it gave me a pretty good idea of what I was dealing with. Not really exact, but it worked for me for many years without ruining a weapon worth more than I made in 3 years.

l'd also just use my eyes and common sence.
You can get a pretty good idea of where you are at.
It would make me more than a little worried to close a 100K plus shotgun or double rifle on a guage.
This is the way that I have always done it and it has worked fine for me.

A piece of clay and a depth guage could be used if you were very careful for a more exact measurement.

John K

Jim Watson
June 10, 2010, 11:57 AM
Do you think Plastigage as used on automotive bearings would work to headspace a break action?