How Does A Gunsmith Set Headspace?

[7mmWSM]

I've owned over thirty-five guns over the years but have never had any problems so "headspace" or "excessive headspace" are just terms to me. I have a chambered barrel that I may or may not have installed on one of my rifles and it dawned on me that I really have no idea how a gunsmith adjusts the headspace when he installs a new barrel. I'm for sure not going to try to do it myself but am curious just how it's done. Can someone give me a quick overview? Thanks.

[brickeyee]

With a go head space gauge.

Cut until the action just closes on the gauge.

Check with a no-go just to make sure.

I set up in a lath with a dial indicator so I know when i am even getting close.

[James K]

The normal condition is that the gunsmith buys a barrel for the desired caliber. If he knows the cartridge, he can buy a barrel that is what they call "short chambered" which means the chamber is only partially cut. After he installs the barrel he uses a chambering reamer to bring the chamber into specs so that the bolt will close on a GO gauge and not close on a NO-GO gauge.

But with a takeoff barrel, things can get complicated. If the existing chamber is just right, fine. If it is short, he can do as above.

But if the chamber is already too long (and the bolt will close on the NO-GO), then he has choices, mostly depending on the rifle. If the barrel has no sights, he can easily turn down the shoulder a bit so the barrel screws in further, and then he will adjust the end of the barrel and recut the chamber with a reamer, as above. (Barrel markings may be in the wrong place, though)

But if the barrel has sights, he will have to turn down the shoulder and cut an additional thread so as to set the barrel back one full turn. With sporter barrels, this will usuallly work OK, though there may be too much gap in the barrel channel of the stock if the barrel is tapered.

But with military barrels or a rifle like the M1 rifle, setting the barrel back is not usually an option, since it will mess up the handguard, the bayonet attachment, and (if applicable) the gas port. As a rule, no one tries to use a take-off military barrel that has a long chamber, since the additional work would be more than the cost of a new barrel.

Jim

[HiBC]

If we use the example of a bolt action rifle,say a Mauser,
We can get an idea of where we are with a depth mic.Measure from the receiver ring face to the bolt face.Write that number down.Measure from the breech end of the barrel to the shoulder that meets the receiver ring.Subtract that number from the first number,and you have a theoretical number the headspace gage should protrude from the breech as you chamber.Do not trust it completely,of course,but it gives you a reference to rough to.

Then,by hand with a tap wrench,a few chips at a time,you cut,clean,and try a headspace gage.This part is usually done with the barrel assembled to the receiver.

[James K]

Some folks have worked out other ways, but the normal way is to use the GO gauge to see how close you are. Then, ream a bit, wash out the chips, try the gauge again, and so on until the bolt closes on the GO gauge. It should be obvious that all this is done with only the barrelled action, but I was asked by one poster how to keep chips and cutting oil out of the stock and magazine well!

You can't use measurements that don't involve the bolt because headspace is determined by the distance of the reference point to the bolt face and not only will each bolt will be slightly different but the wear on the bolt seats will vary with the amount of use the rifle had previously.

(The GO gauge is used to ensure that the longest cartridge that is within specs will chamber; the NO-GO ensures that the shortest cartridge that is within specs won't stretch enough to separate. The Field Reject indicates that the point has been reached where that shortest cartridge could separate.)

Jim

[LongRifles, Inc.]

How I do it:

First, none of my barrels come threaded, partially chambered or with any feature whatsoever aside from the outside contour and the hole with twisties down the middle.

You set it up and indicate the bore to run concentric with the spindle centerline of the machine. Since not all machines are created equal it behooves a good smith to own a lathe with a spindle that has very, very little runout.

Once this is done (and there's about five different ways of doing it and it all depends on who you ask as for what's the best.) I have my own which is (seriously) a little different from what 90% of the industry does.

Ok, now you turn your blank, you put the threads on it, and you establish the breech clearance. (distance from back of the barrel to the face of the bolt) In almost all cases I run mine at .015". You can slide rule, computer, calculator your way through this and get there. I like simple and dumb. I take a piece of soft solder and dab it to the bolt with a spot of grease. Then I rotate the bolt into battery and allow the breech to squish the solder against the bolt lugs. then measure the solder with calipers at the squish part. Now I KNOW what it is. Leave the computers and graph paper in the desk drawer. You measure all this stuff to initially set your distances with a depth mic. Just strip the bolt of anything actuated by a spring and plop it into the receiver. Then measure from the receiver ring to the face of the lugs and the face of the bolt ring. (not the bolt face) Add your recoil lug thickness and subtract the .015" breech clearance(or whatever you want if you decide you must run it tighter) For a cone breech I just literally "guess" with a set of calipers. If I'm short the solder trick will tell me right away. I use this for actions I've not barreled before. All my CNC programs are archived for each specific brand/model receiver that runs through the shop so that later in life when the next one comes in I have less work to do while getting the same results.

Now your ready to chamber. I'll cram the reamer in there till I'm getting "close". Close means around .100" inches away. It's an arbitrary figure that I guess just based on experience and the little scribe lines on the reamer chip gullets.

Now I drop the gauge in the chamber and screw the action on. I'll have the bolt in battery and screw the action on till the bolt face hits the back of the gauge. Then I measure the gap between the face of the action/recoil lug to the shoulder of the barrel tennon.

I'll run that number added to my last z position with the reamer and then bump it an extra .004-.005" to allow for thread crush, tennon elongation, etc.

My target is to have a GO gauge drop in and the bolt handle falls under the force of gravity. Then I stick a piece of .001" shim stock to the bolt face and the bolt should not want to rotate. This is GO+.001" in my shop and its what I strive for with all the precision guns. A working gun or wildcatted wiz banger I'll allow to go to GO+.002" just to have a little extra room for the guy forming brass or buying whatever is on the shelf.

Understand this is "nutshell" laymans explanation. I use a CNC slantbed turning center (over 70K investment) with some crude programming elegance that allows for ultra close thread fits. They say it's impossible to depend on a threaded joint to have a part center itself. I don't believe it. I barreled a Nesika K action two nights ago that when the action was threaded onto the barrel just for kicks I threw an indicator on the OD of the receiver. It measured a TIR (total Indicated Runout) of .0004". Since I once worked as a senior production manager for that company I know how exactly how the actions are made. The OD's of the receivers are cylindrically ground concentric to the honed receiver bore. My point is its a qualified surface so I feel pretty good in stating that it IS possible to depend on a threaded joint to center itself so long as the parts are made well and some care is taken during the threading process. This isn't an isolated moment as I often do this when working with higher quality custom actions (Nesika, Borden, Defiance Machine) just to see where things really end up.

that's my story and I'm stickin to it anyway. Sorry for the long post but there's really no short answer to the question.

This has worked well for me the last 12 years.

Cheers,

Chad

[brickeyee]

You can't use measurements that don't involve the bolt because headspace is determined by the distance of the reference point to the bolt face and not only will each bolt will be slightly different but the wear on the bolt seats will vary with the amount of use the rifle had previously.

Sure you can, but it requires tighter than regular tolerance control.

I do not do it, but you can get a barrel chambered for a Panda action by calling with the action serial number and saying what you want chambered.

You need to make sure you have the correct bolt face (or purchase another bolt) but when the barrel arrives you can screw it on and start shooting.

Untapered threads and square mating surfaces make barrel changes easy.

[James K]

How do they compensate for worn locking lugs or battered lug seats? Or bolt swaps? Otherwise, if the rifle is made to tight tolerances (which costs money), there would be no problem.

Of course barrels like the Savage that can be adjusted, then locked in place make things easy.

Jim

[brickeyee]

Otherwise, if the rifle is made to tight tolerances (which costs money), there would be no problem.

Panda actions run just below $900.

No trigger, no barrel, no stock.

You can set up the whole thing from the forward face of the steel insert in the aluminum action.

Even new bolts can be ordered with just an action serial number.

[James K]

Assuming that all rifles leave the factory with good headspace, the main reasons for a rifle to acquire excess headspace are wear on the bolt lugs, wear on the bolt lug seats in the receiver (or barrel for the few actions that lock directly into the barrel), or compression of the metal in those same areas.

While wear/compression of the bolt lugs would be taken care of with a new bolt, I would think that an aluminum receiver would be very susceptible to compression of the lug seats. I admit ignorance of that action, and maybe it is used in the type of rifle that isn't fired very much, but unless they have some trick, I fail to see how the action would be immune to the kind of problem that affects other rifles.

Jim

[LongRifles, Inc.]

Jim the Stolle Panda has a heat treated steel insert up front for the barrel tennon and the lug surface. the bolt is a remmy clone design.

I have one in my shop right now that I'm building for a client.

It's a decent enough receiver and they shoot well when built right. I personally wouldn't own one but fundementally there's nothing wrong with em. Lots of 1K palma shooters have good scores with panda actions.

Chad

[brickeyee]

The aluminum is just holding the steel insert.

With tolerance control in the insert there is no issue.

Bolts do not 'wear' unless abused, or fired for many thousands of rounds.

You get what you pay for, and any number of the BR actions hold tolerances way better than the run of the mill actions.

I do not even recall a 'stock' mass produced action (or even a re-worked and blue printed one) winning in BR in many years.

[James K]

All true, but I also assume they aren't fired very much. BR is not like a Perry shooter who fires thousands of rounds a year just to keep his hand in.

Jim

[brickeyee]

I uase my Panda action for live varmint shooting, and often go through may thousands of rounds a year.

Well made guns do not tend to have a lot of wear or changes in bolt lockup.

It is the less well made ones with only partial lug bearing that set back more easily.

If only 50% of the lug area is in contact, the loads on the lug just doubled.

If only one lug is bearing and at only 50% the loads just quadrupled.

BR loads often tend to be rather 'hot,' so well made actions are par for the course.

Panda actions have a solid flat surface for the barrel to seat against were the steel insert is milled flush with the aluminum at the front.

There is no thread taper or incomplete threads used to lock barrel to action.

You can unscrew a barrel from a Panda action, screw another on, even at the range, and start shooting.

If the barrel is torqued tightly head space cannot vary.

[7mmWSM]

I very much appreciate those who weighed in and helped me to better understand this process. I'm sure as heck not a machinist so some of the descriptions were "Greek" to me but I do have a handle on the process. Again, Thanks for taking the time!

[F. Guffey]

A quick overview, I purchased a 30/06 barrel from USAMIDWAY that was short chambered? meaning they started the chamber I was to finish it. I set the barrel up and chambered a round in the barrel then measured the protrusion from the barrel, the protrusion was .200, in my opinion the barrel was toooo short chambered, I called them, they did not get upset, I finished the chamber with .114 case protrusion.

Before I started reaming the chamber I measured the distance on Mauser action from the barrel seating (C) ring to the bolt face, the measurement was .115, in the perfect world I should have .001 thousands head space, once the face of the barrel is clean and dry and contacts the receiver seating (C) ring the chamber does not shorten (much) when the barrel is secured to the receiver.

After installing the barrel I would expect from .000 to .001 thousands head space. "A quick overview" I do not shoot gages, I shoot ammo I load, not always 'reloads' more times than not I form cases from longer cases, as with the 30/06 case I use 280 Remington cases because of the extra length from the head of the case to it's shoulder, when forming 280 to 30/06 the shoulder is formed .051 thousands further back to chamber and will chamber by .005 thousands (in the perfect chamber)., when forming 280 to 30/06 I start by forming the shoulder back to 1.958 or .010 longer from the head of the case to it's shoulder to chamber in the perfect chamber by .005 thousands then progressively move the shoulder back on different cases until I have at least 8 cases that are between .000 (minimum length to no go-gage length, to verify chamber in a barrel and check case head protrusion.

The 280 cases are not necked up, this eliminates confusion them with cases that are to be sized and and loaded. The case that is .001 over a no go-gage will not chamber in a rifle that that does not have an excessive length chamber, again, I have a M1917 Eddystone with .016 head space, when forming cases for that rifle, I stop forming the shoulder at 1.962 (moving the shoulder back) from the head of the case to it's shoulder, this leaves me at firing the rifle with the equivalent of .002 head space and keeping up with case protrusion the .014 adds to the .090 the rifle case with leaves .104 protrusion, .006 less than the Mauser with a head space of .005, AND, with commercial cases with .260 case head thickness gives the case addition supported case in the chamber over military cases.

With out a head space gage, did not say I do not have them, I said I do not use them, I have found they fit nothing, I do use them to verify a sizer die adjustment or case head protrusion, before I order one, I will make one, two or 10 of them for less than the expense of postage.

F. Guffey

[Harry Bonar]

Sir;
LongRifles Inc. - you know what you're doing setting it like that!
Harry B.