Rifle Headspace Gauge Facts and Lies 

It is such an easy tool to use and so helpful.

Sir I will pose this question to you. If you neck size ,or bump size a cartridge case which has been fire formed to a specific weapons chamber then that case will no longer bottom out in your case length gage. This is because the case has now taken on the dimensions of the weapons chamber. Since each chamber does have a machined tolerance lets say + -.005 for example there will now be a difference in your fireformed case and that case which is Sammi Spec. I do agree with the rest of your video and note that any case that will fit into a case length gage after full length resizing assuming that your C.O.A.L.is within spec should function in your weapon. With that said if you set your bullet depth to say .010 off the lands you must now check your weapons action and magazine for functionality. Now your round may not chamber because it is hanging up on your magazines lips. This C.O.A.L. of course must be altered to allow your rifles bolt to close. Again note that C.O.A.L is more critical on an auto loader than a bolt gun. The Cartridge case length gage is an excellent tool for use if you only FL resize your brass, but can certainly throw you if you neck size ,or bump size. To clarify I have several weapons chambered in 5.56 mm. two of which are semi auto. ( here FL resizing for functionality would be the correct way to go.) (Semi-automatic) My 3rd rifle is a bolt action which is chambered also in 5.56 mm. ( here I neck size for accuracy). The head space gage will not bottom out because of the case webs fire formed dimensions. This fact remains a constant if you either bump size ,or neck size a case. Just my thoughts,& observations.

For a couple bucks more might as well get the LE Wilson

Believe me I don’t have a wealth of knowledge. This was published 4 years ago and I am still a beginner. But thank you for the kind words.

Thank you for the important info.

Someone else mentioned that a couple of years ago too. None of us are perfect. 👍

mechael m Technically a case gauge is not an ammo checker. Lyman makes an ammo checker. I really can’t tell you if your ammo is “safe”. If the unloaded brass fits a case gauge correctly after sizing it probably is alright but not a guarantee.

I guess it depends on the barrel in your rifle. My fired cases won’t go in unless resized.

Kamil Klein Yes, you are sharp and not the first to point out my error. Thanks for the comment.

Thanks for clarifying I also thought the datum line was about halfway down the shoulder

I will assume that when you check the primer side that the base is between the upper and lower ledges so you know that the datum (neck) is correct. You then flipped it over, placed on a table with primer side down and brass was lower than lower than lowest ledge therefor you overtrimmed your cases. When you put your bullet in you may not be crimping in the cannelure. Safety? I don't know but your brass does not meet specs. I guess one risk might be a compressed powder charge from a too short case. I admit that I don't know the consequences of firing this but I am curious and I will google it. Not sure what 12cpr is if you can enlighten me.

If the cartridge will fire there is one more thing to think about here. BTW this shoulder setback problem is what caused so many misfires with boxes of remingtons 300 BLK 120gr supers awhile back. I think from your description that is actually what you have done, the case does not have to be too short in this instance. Be sure to correct this at next loading or your cases will stretch at a point just above the solid base and cause a thinning that could cause a case head separation. You don't want that to happen! I don't think one firing will cause that, it did not in my instance of using Remington's screwed up ammo and I have reloaded them again successfully after they were basically fire formed to proper dimension. Just don't fail to raise your sizing die next go around and set the shoulder back too far again.

risky business, as long as you are using full length or small base dies for your rifle, your chances of getting the case below the headspace checker is slim to nothing! you may be trimming the case neck down to much and getting your overall length to short, but a few thou short which is no real danger, but cutting your pistol cases down to far is another matter! especially in semi autos! you have a real chance of blowing a primer, and crap blowing all over your face! as far as rifle the only way your going to get to short on the case body is if the manufacture made it that way (when using the dies i mentioned)if your reloading cases you shot there formed to the chamber and will only be a few thou long. but good luck and be careful with that pistol brass

dragonfly fab Was that after a full length resize or before.

Anthony Murphy 😀

I can’t answer definitively as I don’t know if your cases need to be trimmed or not. Case gage tells you. If case length is okay than the case should be good for reloading assuming no cracks or other defects. You can also measure case length with a caliper.

@@TheRotorhound so if it fits the case gauge and brass is ok charge is right it should be ok the hand loader only sizes the neck as you can probably tell I'm new at this

obviously he doesnt have a 6.5 CM or a 450 bush

@Ray O...or .300 Blackout (even though it’s come down some in price it’s still spendy)...his video is still informative 👍

I bet he's reloading it nowadays!

Jose Lee Not really. Ammochecker checks completed loaded ammo (rifle). Case gage checks case alone mainly to set resizing die and there is a RU-vid video which shows a cartridge passing a case gage but not an ammochecker. Case gage also in rifle doesn’t need bullet. Pistol gages are in my opinion are ammocheckers.

Chris Staples When you say not sitting flush, you hold the gauge up in the air, drop your resized case in and what happens? The base is not dropping into the gauge?

@@TheRotorhound the case head doesn't sit flush with the gauge like a factory case does. I can tell the case head is slightly bent. Therefore it won't sit in all the way

Chris Staples Extractor must be bending it. Does it still shoot okay? I don’t know what to do in that case. Don’t know of any dies that recondition the base. Wonder if they would pass an ammo checker.

@@TheRotorhound yeah, like I said, they load fine, they extract great. Very accurate rifle. I've run about 40 hand loads through it, and about 100 factory loads. I bought it brand new, so perhaps it will ease on the bending as it gets broken in. I've loaded for bolt guns and lever actions, never before for auto loader.

@@TheRotorhound I know that extractor is alittle rough on the rim of the case. I had an m1 garand that was the same way.

👍

With the gage flat on a table if the brass extends beyond the top of the gage it should be trimmed. This is after going through the resizing die. You can confirm case length with a caliber

@@TheRotorhound I was asking about resizing not trimming. My fired form brass fits in my case gauge but the datum line grew 0.006 do I need to resize if it fits in my case gauge between the lower and upper step

@@boricuaarecibo9259 No. Should be good to go. Thought you said the case was above the top edge of the gage. I would still measure case with a caliper.

Remember that the gauge is used to set your resizing die to specs. The brass may be new unfired so don’t get hung up on the gun chamber. Yes I guess you could put the base of the case in backwards to see if the rim fits into the base end of the gauge. Never had one that didn’t but I guess it’s possible. For fired brass, the case lengthens and if after resizing you first examine the base to see if it is between the upper and lower limits of the gauge, then place the base end on a flat surface and see if the top of the brass is between the upper and lower edge of the gauge (do not push the shell up with your finger). If the brass extends beyond the upper limits of the gauge it should be trimmed. If the brass is below the lower limits of the gauge it is too short. This is all for rifle. Not pistol.

@@TheRotorhound I will put my calipers to use and measure and the diameter of the gauge to that of the case at the base. I cannot imagine the headspace being so vast that a case would stretch to this extent without the chamber being subjected to destruction.

@@crawford323 I don’t really understand your comments. Let’s say you have an unfired case, new from the manufacturer. You do a full length resize, put it in the gauge and it checks out perfectly. Good to go. That tells you two things, your resizing die is set right and the case length is correct. Screw in your resizing die a couple of turns, resize the same case and try putting that in the gauge. Do this with a .223 case. You should see that the base of the case will actually go lower than the low limits of the gauge as you have moved the datum line lower. That case is no good. Readjust your dies.

@@TheRotorhound No my issue is not with new brass but with once fired. The base portion of the once- fired case will not slide the total way to the point where the shoulder of the brass meets the shoulder of the case checker. The case sticks out .325”. I measured the point where the case stopped without forcing it into the checker. It seems the once-fired brass is now slightly oblong near the base. If this is a fingerprint of my chamber, is there a problem with my barrel? The gun is an early 70’s model and shoots well. Of course after full sizing the brass, it passes the checker with no problems.

@@crawford323 If it passes the gauge after full length resizing then your die is set right and you are good to go. That is why you don’t try to put a fired brass in the gauge because it will not go in. Firing the round stretches the brass. Only resized brass goes in the gauge. Your barrel is doing what it should. If it fits the gauge after resizing great. Some people reload specifically for one rifle and do not full length resize. Their ammo may not meet Sammi specs but work in their rifle. I reload to Sammi specs. Realize also that a case gauge is not an ammo checker. I use one on completed ammo.

Bobby Mat Bobby, I would go to lewilson.com site to see all of the available gages and how to use them. Great company.

Thanks for your response, I'll check them out.

Tom Maryott Thanks.

Correct.

Now knowing that holding the head of the brass with your thumb is wrong and the gage should be placed on a flat surface why do it? Perhaps you should consider using an ammo checker like Lyman makes. If it can’t fail. I did see a video where the completed round passed a gage but failed an ammo checker. I have both. I still haven’t reloaded any rifle ammo in years. Lazy I guess. You seem pretty knowledgeable yourself.

@@TheRotorhound Hi and thanks your reply. In truth there really is no 'excuse' if knowing the proper way is laying it on a flat surface. My 'reason', apart from habituation, is mostly (and critically) a very small working space/speed. [I modified/fused a couple of Skil metal saw horses together to make a portable reloading station, which I am using in my tiny apartment - a work in progress.] So I will have to fabricate a dedicated flat surface convenient to the trim station if I am to continue the go/no-go gauge application. I think my fingernail step has maybe accidentally saved me from over-trimming, which means they are likely then flush when on a flat surface. Question: Couldn't the gauge be (theoretically) manufactured so that proper trim length is with the base fully inserted/'finger pressed' (adding +.005 to the trim side)? Or I am still missing something on the gauge's design? I watched a Wilson video on it's use once, and I admit (for my specific project) it seem very confusing. The instructions refer to 3 methods, I deferred to the third for 'universal fit'. Just when I think I understand something and get comfortable with it I discover I didn't have the whole picture. I will check out the Ammo Checker, hadn't heard of it. Thanks much!

@@controlledburst I think you are missing some of what the gage is for and that is in rifle to set your dies. You run your case through the resizing die and adjust your die so that when the case is flat on a surface the top of the case is between the upper and lower edges of the gage. The die can move your datum line down if screwed in too far, so you unscrew the die a little bit. That case is wasted. Pushing up like you do makes a bad case look good. Maybe not if not too much. If your die is not screwed down enough the datum line will be too high, screw the die down a little and run the same case again. For completed ammo a ammo checker works great. I personally have never had ammo that was good in my gage fail an ammo checker but I saw a post where a guy showed good in a gage but no go in an ammo checker. A perfectly set die with the case flat on a table in the gage will show you if your dies are set right and if you need to trim. By the way, I use that harbor freight table for reloading, heavy and cheap on sale. Does good for me. Try putting a case flat on a table and not pushing up and let me know how it goes. Curious.

@@TheRotorhound Thanks, yes I do understand the intent is to assure head-spacing after the resize process. Though I refer to my use as 'go/no-go', in the end making sure that the tolerances at each end is more-than-this and less-than-that is for expeditious processing and to avert using calipers on every case, while ensuring no FTFs. I keep track of lots and will test a small percentage (I fortunately also have 10 AR builds that need testing too). I use RCBS AR small base dies. The FLR learning curve was a head banging step for me as well - it was an article from a Kiwi down-under that switched the light on (regarding the 'cam over' issue - though true cam over is on few presses). As per your comment I did grab a handful of sized/trimmed cases (no primers) and used a smooth laminated computer counter for flat surface. I placed them all (about 15-20) on the counter with the gauge over them, the neck is still below the max index as you would expect. But when I run my fingernail scrape in the low shelf of the gauge and it still grabs the neck, above minimum. In fact I modified a chopstick (because they're tapered) so that I could lightly ram it in the case mouth and have it grab the case to lift up and down to see/feel any difference and, if there is any, it is almost imperceptible. Odd unless I happen to be right in the sweet spot. When I first acquired equipment and got the Wilson gauge I took a factory, white label Federal LC M193 5.56 round and checked it in the gauge. The base below max (essentially bottom) and - while holding the base with my finger - the neck was flush with minimum. This is the standard that I have (intended) to replicate. One observation about this does still leaves a question in my head: If the case is sized to be flush with the minimum gauge tolerance, then when laying the base side on a flat surface, it will drop slightly and you are guaranteed to have a small gap (.005

@@controlledburst Sounds like you are good. First check should be dropping the resized brass in with the head up and not on a table. Head should be between top and bottom of gage edges. If it passes you turn it over, lay on a table and see if it needs trimming. Easy. No fancy flat table needed. If first step failed readjust your die. I still use an ammo checker, especially if you are making lots of ammo as the checker is cheap and ammo is expensive. Good luck. 👍. Oh, if you are doing 10 builds maybe you need to get a real set of go no go gauges to make sure your barrels are set up right. Another topic.

You are correct.

Rich Foster Why would the gauge be sitting at an angle? Whether a case is in the gauge or not when placed on a flat surface it will not be at an angle.

@@TheRotorhound You right. I thought the video showed the two sides of the dado cut to be at different heights. But why would you measure OAL by allowing the headspace to fall down a smidge to the table? If headspace is good, meaning you put some pressure on the case in the gauge, then the snout of the case should end within OAL spec. Why would you take that measurement in the gauge by allowing the case to back off of datum? I say this because datums are 1) not perfectly round, and 2) the two datums are not concentric, and because of this no two rounds will seat exactly the same way. OAL really needs to be measured when the case is ok'd at headspace check. So like some other comments, not sure why you use the gauge to measure case OAL by placing the rim and gauge on a flat surface. I would use this gauge for headspace only and then use caliper to get OAL.

Rich Foster If you lay the gauge on a flat surface with the rim down and the bullet end of the case up and the case has been resized case overall length will be good if the brass is between the upper and lower edge of the gauge. If you manually push the case up from the bottom you may think your case is too long and needs trimming. I see this on some videos and it is wrong.

William Parks When you say round I assume you mean case. So you resize, place in gauge and have it flat on a table and the top of the case is below the lower edge of the gauge. That means the case is too short and that you have trimmed it too much I guess. Technically a reject. I have never had this happen and I almost never reload rifle but this would be out of spec and if it were me I would dump the case. To be honest, I don't know the risk of reloading if it is just barely below the limits and perhaps more experienced reloaders can jump in. I tend to lean staying within specs as the safest way to go which is why you use a case gauge and an ammo checker in the first place.

Wow. This is when you need a Sheridan open case gage to see where the hangup is.

@@TheRotorhoundI’ll try that next. I’m using a Frankfort Arsenal M Press and the shell holding solution is pretty squishy. Doesn’t give me confidence it’s consistent, but so many people swear by them…

Thank you. Pointed out by multiple commenters.

@@TheRotorhound We can all have a slip of the tongue. I’ve had many. 😉

Yes.

How about you get a heart instead of thunder. When I screw up everyone posts.

R Nel Good points. I don’t shoot enough rifle to bother with reloading as the work involved and case prep just wasn’t worth it for me. I definitely understand your point. Most of my rifle was plinking with Ar15 55gr ammo relatively cheap. Or AK47 steel case non reloadable ammo. But I do save my rifle brass.

[Laughs in .450 Bushmaster] :D

Try .300 H & H, .338 Win or .375 H & H...all over $75 a box of 20 premium hunting ammo up here in Alaska. I can get a box of 50 premium bullets for these cartridges for $30.

Gauge doesn’t give you a numerical value, calipers do. I use both.

Thanks. The real smart thing is to buy lots when it is cheap, which I did. Lots.

Jimmy Ratzlaff Yes you are correct. It is hard to screw up and not get caught on the internet. I was wrong.

Are you referring to go-no go gauges?

@@TheRotorhound yes I am , that is a true headspace gauge , and what you are showing is a case headspace length gauge .. if you call them both headspace gauges ( and I suppose you would not be the first to do that ) it is confusing .. so most gunsmiths say that one in your video is a headspace case length gauge and the go no go's are just plain old headspace gauges . This is for less confusion .

@@TheRotorhound you can also place a fired case from a gun with questionable headspace in the case length headspace gauge and see if the brass is expanding to get an idea of the gun's headspace , this obviously requires firing the gun before you have checked headspace though .. or cut a spent case fired in a safer gun in half drill a hole in the spent primer , thread the hole and place a bore brush in the there , grind a little of the rounds neck down and make your own go no gauge by closing the action on it and seeing how it fits in the case length headspace gauge , this is handy to save money on buying various go , no go gauges or when using some of the rarer wildcat rounds ...

/\ that's a trick not many people know about .. btw .

@@davidfriend1919 You are absolutely correct.

Why don’t you tell us how you measure brass hardness. I personally have no experience with annealing so this video doesn’t go into that process. Thanks for the comment.

You.are correct. Someone posted the same information 3 years ago.

That works, just slower.

popstooge To err is human. You are correct.

Robert Melrose Lyman lists it as a case length/headspace gauge. This does not measure the firearm headspace. Hornady and perhaps other companies make gauges to measure firearm headspace and there are also go/no go gauges available.

Ruske Eblue I am sure you are correct about this but for those that want to set their reloading dies correctly the case gauge is the way to go. What exactly do you measure when you use a digital caliber? Case overall length? Primer depth? Datum line? Or you can pop a case into the gauge. If passes your dies are good.

@@TheRotorhound Measuring a new case for the given round then FL resize touching the shell holder and a little overcam, yes use the case gauge. Fireform a round and then only setback shoulders to minimize case stretch while still fitting your chamber. Semi Auto .003 to .004. After fireforming I use the comparator to set the die and then case gauge just to see and sometimes of course not being sized to SAAMI it will fail the case gauge, but guess what, fully functions and brass is less stressed. This makes for why I load for my rifle rounds.... accuracy. I realize this vid is older, but I load for rifle and buy pistol rds. I feel this vid is however a better explanation on how and why for case gauge Good Job and thanks.

Pat Cooper Why do you say that?

@@TheRotorhound well it almost seems you criticize the tool for what it is. I have one and it does what its supposed to do for me.

Pat Cooper I have one for every caliber I reload.

@@TheRotorhound i just have one for 223 and works for my needs !

Jerry Avalos SGAMMO.com. I agree that reloaded ammo tailored to your rifle is better but if you want plinking ammo for an AR15 you can spend less than 30 cents. For my uses rifle ammo is too labor intensive to reload for plinking. I also shoot an AK47 with cheap steel cased ammo and that is really cheap. If you are out for the best accuracy in a given rifle reload cases fired from that gun.

I bought a ton when it was cheap.

Lyman calls it “A case length headspace gauge”. I didn’t make that up. I agree that it is not the Hornady type headspace gauge that you are describing. These gauges are to make SAAMI ammo and are used to set your sizing die properly. That may not make ammo that properly headspaces on a particular rifle. You are correct in that this gauge doesn’t measure headspace in a specific rifle. Realize also that ammo that passes an ammo checker may not headspace in a particular rifle. Not all rifles pass go/no go gauges.

This is not a guide to reload, only info about the gages. I shoot rifle too, mainly steel ammo and I save my AR brass and may reload in these expensive times. I am personally not into long range target rifle and stick to handgun ammo. Hopefully my video helps people make better more accurate ammo. I am not a RU-vid paid channel like most of the gun videos are. Just an individual. If you have some videos let me know and I will watch them. Have a nice day.

Nope. Still have a ton of rifle ammo. Also much AK47 steel stuff. Zombies and terrorists beware.

I still have a ton at 30 cents a round and a ton of components. Buy and hold when cheap. Maybe I need to make a video. Lol

@@TheRotorhound I need to become a hoarder next year.just bought reloading equipment but no material Lol

@@linavu5834 Boy Scout motto, plan ahead. When cheap buy lots. As long as it is in temperature controlled area it lasts forever. Welcome to reloading. I started about 2013 when we had a shortage too.

@@linavu5834 The other way to go is to get an AK, steel Russian stuff, will be cheap and you don’t have to reload. Buy a lot when cheap. I did that too.

@@TheRotorhound will do thanks for the advice so next built upper will be 762x39 to expensive in Ca now for a AK

Jose Canisales Case overall length is measured with the base of the gauge on a flat surface. Read the instructions that came with your gauge. If you're datum line is at the proper spot on the case as set by your dies and the case gauge is placed flat on a table base down the top of the brass should be between the upper and lower edges of the gauge. The commercial Fiocchi ammo that I demonstrated that on shows what I am talking about. So, what part is BS? Now if you set your dies wrong then you will not measure Case overall length. If you measure on a case gauge from the inner surface on top to the inner surface on the bottom with a calipers you should have a short Sammi spec. If you measure from the outer edge to the inner opposite edge you should be right on the button. If your die is set right and you're holding the gauge up above a table the base of the brass should be between the upper and lower lips of the gauge. Then you know your datum line is proper and you're dies are set correctly. Then lay the gauge on a table primer side down and if the head of the case is between the upper and lower edges of the gauge your length is correct. Do you understand this? Try it yourself with some commercial ammo and see for yourself.

@@TheRotorhound The answer is that it is not that important. In fact, it is more accurate to measure from the datumline since that is where the case stops in the chamber. Many of the newer trim tools sit on the shoulder and the neck thus becomes the same length even with variations in headspace.

If your case is too short the datum line may not reach the stop point in the chamber. This is to make Saami specific ammo not to case fire a specific case to one rifle.

@@mortenbreiland3984 The case gauge is designed to set your dies properly and to make sure your col is correct.

@@TheRotorhound The case is pushed forward by the ejector button or by the firing pin. If the headspace of the case is too big, the neck will be too long and will go further into the chamber neck and in the worst case too long. For those who make ammo after Sami for a hunting rifle or an auto, this is completely irrelevant

Lyman calls them case length headspace gauges. They do not measure the headspace of an individual cartridge in a particular rifle. These gauges are for setting dies to achieve SAAMI specs. You can feel free to write Lyman and ask them to change the name of their gauge. In no way did I attempt to measure the headspace of an individual rifle with this gauge. Gavintoobe has some videos showing tools for measuring actual rifle headspace and I am sure there are others. If you feel that I am wrong please comment again. I am still in the learning phase myself.