Gunsmithing Excessive Headspacing, please school me

[GasLight]

OK I was just headspacing a barrel onto an action a couple days ago. I made the stupid mistake of taking my measurements with a .01" accurate calipers, and ended up putting it together only to necessitate taking it apart and starting over after the no-go gauge easily chambered. I was goaling for somewhere around .002" or less over the go gauge, and after the bolt closed on the no-go I realized my mistake. At any rate, this all got me to thinking on excessive headspacing and what the problems are with it. I would in no way leave a barrel that far over (~.01" over), but when I was explaining the mistake to my wife and showing her on my better pair of calipers, .01" is really difficult to show as being a huge problem LOL. So I guess my question is, where does extra headspacing become excessive, and what are the problems associated with it? I would guess when most brass is blown out to a 40° improved cartridge, it would experience more stretch than would a chamber that was .01" over. I am not trying to shirk by here and start the thinking that .010" is close enough, not by any stretch, I think anyone interested in precision machining and gunsmithing should be able to hold tolerances like this. I am just asking for the discussion of excessive headspacing.

Thanks for taking the time to read and hopefully respond.

Dave

 

[wnroscoe]

Re: Excessive Headspacing, please school me

Dave,

I try to have my headspace set to where I can just feel the go gauge as I close a stripped bolt on it, maybe .0005” over a go at max, if over at all. On BR rifles, I want it to be a slight bit snug on go but not tight. As long as the bolt closes on a go and not on a no go you’re OK but that’s only a difference of about .003" / .004", .010" over a go is way too much. The problem is the stretching of the case and possible case head separation at firing or primer blanking. The standards of SAAMI should always be adhered to when chambering.

 

[GasLight]

Re: Excessive Headspacing, please school me

William,

I greatly appreciate your input, and I agree completely with what you are saying. I was aiming for less than .002" with this particular barrel as being acceptable, and wasn't trying to justify the .010" at all. My question is based in WHAT makes excessive headspacing dangerous, and where does it occur. I have seen no-go gauges as much as .006" over, and a field gauge is .008" over IIRC, which is pretty darn close to .010". I definately personally would not allow a chamber to be even .006" over, but this is what got me thinking about the whats and whys.

Thanks again!

Dave

 

[Lt. Arclight]

Re: Excessive Headspacing, please school me

Excessive headspace will eventually cause your brass to fail at the web.That is a catastrohic failure-especially with the bigger magnum rounds. What caliber are you working on. I hope you aren't talking about a 408/375 or a 338 LM. Quality go/no go gauges-like Dave Manson's are right on spec. If a stripped bolt easily closes on a NO GO gauge-that is a bomb waiting to go off literally in your face.

wnroscoe also makes a point-if the headspace is too great the case,registering on the shoulder is so far into the chamber the firing pin may not be able to strike the primer.

 

[GasLight]

Re: Excessive Headspacing, please school me

This is a .260 match, and as I stated above, I am not trying to advocate or suggest that I would leave it this loose, that is the last thing on my mind. I was just asking what the problems with excessive headspacing are due to the fact that when explaining the differences to my wife, it was hard to explain that .010" was a huge over-sight, when showing her what .010" looks like.

I understand the primer blanking, which makes a bunch of sense. This is one of the things I didn't think about, that the firing pin protrusion may not be enough to overcome a .010" deficit.

As to the stretching enough over time to create a problem, this would be for someone who is reloading and full-length sizing every time. But .010" would also be less stretch than occurs when you 'ackley-improve' a cartridge. On the .30-06 to the 40° improved version, the shoulder is moved forward an entire .069", which I know isn't all directly from the web, but I would bet that the strech isn't contained entirely to the shoulder either. So, the webbing would be thinner than a standard cartridge to start with, and would be as suseptible to case head seperation as an over-sized chamber?

I appreciate the input, and please remember, I am not in any way shape or form going to leave this chamber over, I am just wanting to learn more about the problems with excessive headspacing. Where it starts and why they are problems

Thanks again!

 

[Lt. Arclight]

Re: Excessive Headspacing, please school me

The big problem is the case is going to stretch at the web-the bottom where it is not encased and supported by the bolt or the chamber.

Forget about the shoulder angle- take a 260 and make it a 260AI-granted you fire-form the cases and they match the chamber perfectly.If the headspace is set correctly the brass grows forward. If the headspace is set on the NO/GO gauge-it's the OTHER END of the case that'll stretch. I disagree 100% the stretch IS concentrated on the shoulder forward and should have no bearing on the condition of the case web if everything is as should be.

In John Hinnant's book on Precision Rifle Barrel Fitting-he has an illustration of the maximum clearance between the bolt and the barrel. He shows Mauser's,Winchester's,Rem 700 and a SAKO and the max clearance is 0.005".

 

[LSandBinc]

Re: Excessive Headspacing, please school me

I would think that not only will the brass push forward but also back. Meaning it would keep slapping the bolt lugs until they fail in some way.

 

[SDWhirlwind]

Re: Excessive Headspacing, please school me

Like William I aim for 0 on a go guage for my pdog rigs and no more than .001 for my coyote, mess around rigs. .002 is more than I allow for myself even though it is well within a No Go.

With brass stretch it is not only the .001 to .004 or so to a No Go that it can stretch but keep in mind that new brass is almost always even shorter than a Go guage, sometimes .005ish under or a bit more on some cases as the manufacturer has their "allowabable" tolerances. So you take their .005 +/- and a chamber on the edge of a No Go and then a couple of full length sizes and your brass is toast. If you fire formed the new brass to your too long chamber and then only neck sized you would come out better but worse case scenario is when FL sizing brass.

HTH

 

[Lt. Arclight]

Re: Excessive Headspacing, please school me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ARShuter</div><div class="ubbcode-body">I would think that not only will the brass push forward but also back. Meaning it would keep slapping the bolt lugs until they fail in some way. </div></div>

Everytime you fire the rifle the lugs are what bear the load, the action is locked tight at that point.The chambered round is always trying to force its way back-RECOIL!! Its just that there always is a certain amount of the case that goes unsupported,that's why there are SAAMI specs that determine headspace. Brass is weaker than steel. When you have a case web failure-you will remember it.

 

[dmgreene]

Re: Excessive Headspacing, please school me

As long as you are reloading for the cartridge you can go over the max headspace. This is no different than a bunch of the wildcats that are out there.
There has to be some way of controlling (jamming in the lands or a false shoulder) where the case stretches on the first firing to keep it from stretching in the web area. After initial fire forming set your die so you don't push the shoulder to far back and your rifle won't know the difference. Look at the 6BRX. Although it takes a special reamer it is nothing but a 6mmBR with the shoulder blown foward .100". You can use a 6br die run up .100" to bump the shoulder back.

 

[GasLight]

Re: Excessive Headspacing, please school me

has anyone done any testing, cutting cases after fire-forming, after a sloppy factory chamber? It would be very interesting to cut cases open and see where the case gets thin, see what the effect of sloppy headspacing is.

AND 1 MORE TIME: I am NOT asking if it is OK for me to leave this chamber long LMAO... I feel like it keeps getting implied that I would leave it there. My goal was to be under .002" not at or above that. I just want to learn what the problems are with excessive headspace, because when I looked at .010" it seems like such a tiny amount. Is the brass really that fickle? Has anyone connected a loose chamber to early brass failure? I'm just wanting to learn here

Dave

 

[GasLight]

Re: Excessive Headspacing, please school me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dmg264</div><div class="ubbcode-body">As long as you are reloading for the cartridge you can go over the max headspace. This is no different than a bunch of the wildcats that are out there.
There has to be some way of controlling (jamming in the lands or a false shoulder) where the case stretches on the first firing to keep it from stretching in the web area. After initial fire forming set your die so you don't push the shoulder to far back and your rifle won't know the difference. Look at the 6BRX. Although it takes a special reamer it is nothing but a 6mmBR with the shoulder blown foward .100". You can use a 6br die run up .100" to bump the shoulder back. </div></div>

Just a quick clarifying question:

Why would the brass stretch first on the case web? The initial response to the case firing, is for it to jam rear-ward into the bolt face, after this forces the lugs back into contact with the action, the only place for brass to flow is forward. I can understand the effect of this on primers, I am just curious if anyone knows why the brass wants to give at the case head first?

 

[shooter53]

Re: Excessive Headspacing, please school me

DebosDave,

I have done the same thing in my early days of gunsmithing. Will the gun work, yes! Will you have catistrophic case failure, yes eventually. Will the gun shoot well, no lousy groups most always accompany excessive headspace or too tight of a headspace.

I have found over the years that optimal accuracy for my builds ususally occurs between 0.001" to 0.003" over the go gauge. Different calibers like different headspace settings.

Hope that sheds some light on the matter. (personal experience)

 

[dmgreene]

Re: Excessive Headspacing, please school me

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DebosDave</div><div class="ubbcode-body">
Just a quick clarifying question:

Why would the brass stretch first on the case web? The initial response to the case firing, is for it to jam rear-ward into the bolt face, after this forces the lugs back into contact with the action, the only place for brass to flow is forward. I can understand the effect of this on primers, I am just curious if anyone knows why the brass wants to give at the case head first? </div></div>

If there is no false shoulder or the bullets are not jammed into the lands when the firing pin strikes the primer it forces the case foward against the shoulder. The thinner portions of the case start expanding first and start forming to the chamber wall which holds the case in place until it gets to the web area which is much thicker. The web doesn't expand as easily so it doesn't hold on to the chamber wall and gets pushed back until it hits the bolt face.

Headspacing standards are so that brass, chambers, dies and so forth can be made anywhere and they will fit one another. If you are shooting factory ammo then you have to have the correct headspacing. If you are reloading and set your dies up accordingly and fireform properly then you can go beyond the maximum headspace.

 

[eddybo]

Re: Excessive Headspacing, please school me

I cut the bolt face in a 223 back .018 and did not correct the headspace. I shot it over 1000 rounds using the same 100 pieces of Lapua brass with the gun in this condition. I was careful not to bump the shoulders back more than .002 when I sized the brass and had zero problems with function or accuracy. If you are building the gun for yourself and just do not feel like correcting it right now, shoot it......but NEVER EVER NEVER put a gun in that condition in the stream of commerce. The safest thing to do would be correct it. I would have corrected the headspace on that 223 but I already had a new barrel on order and decided just to wait for the new barrel.

BTW I understand cutting over headspace......my worst was over .120. I had to replace the barrel, but ended up using the old barrel to build myself a .280AI. Long story on how I did that but it happens, kinda like that boltface mentioned above, long story. I find that I am having fewer and fewer of those long stories. I also find that I am having more of those short stories, "built gun it shot." Looking at my old barrel bin I am over 50 chambers into this hobby, and still love it, even though it will make you pull your hair out occasionally.

 

[GasLight]

Re: Excessive Headspacing, please school me

Awesome information guys, I really appreciate the discussion. The stretch rearward makes 100% better sense now!! Thanks dmg! Again, I will not leave this gun in this condition, as that was never my intention anyway, it just sparked me to start thinking, and now I feel like I understand the whys and whats of excessive headspacing. Thanks for taking the time help me get my mind around what is happening.

DD

 

[kraigWY]

Re: Excessive Headspacing, please school me

Debos, I'd recommending getting a hold of Hatcher's Notebook, he has an excellant chapter on Headspace.

Well worth the read, but way too long to post here.

 

[GasLight]

Re: Excessive Headspacing, please school me

Just to put everyone's mind at ease who was worried about me leaving this long, I just finished now, and the bolt will close easily on the go gauge, but will not close on the go gauge with a single piece of scotch tape on the rear of it.

Thanks for taking the time to discuss excessive headspacing with me.

Dave

 

[x ring accuracy]

Re: Excessive Headspacing, please school me

You saw Gordys trick, lol, it's a good idea and works.

 

[David300]

Re: Excessive Headspacing, please school me

When you fireform the Ack. brass the case still touches at the neck/shoulder area to keep the brass from moving forward and lets it expand outward only.
with a chamber that is to long the ejector is going to push the shell forward and when you shoot the case swells and sticks in the chamber and lets the case head move back and stretch at the web.
just my opinion!!

 

[n64atlas]

Re: Excessive Headspacing, please school me

Headspace by SAMMI specs is a maximum of .010 over the Go gage. That is where a Field gage is set. The no-go is at .006 from the go gage. If looking for accuracy then the less over the go the better. All this is to be able to use factory ammo. If you go over, all is not lost. You can set the barrel back and start over or make your own wildcat by fire forming to the new chamber. Then send three cases to RCBS to have special reloading dies made for your now Wild Cat cartridge.