How does excess headspace occur?

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Lex

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I am no gunsmith so forgive me if this sounds like a silly question.

I have a Model 70 (Pre 64) 30-06 that has been tested and has a bit of evidently inconsequential headspace. It nevertheless shoots better than 1/2 inch on a good day. I don't understand the probable cause of headspace
in this instance or the ramifications for the future but it bugs me.I'm pretty sure the barrel is original and I doubt if it has ever been removed.

Can anybody comment?
 
Probably wear, or a bit of setback over time as the rifle was used. Of course, you don't really know what the situation was when the rifle was new. There may have been little change.
You don't mention how the rifle was tested. It is not unusual for a used rifle to accept a No Go gauge. If the rifle swallows a Field gauge, the situation is more serious.
 
tiriaq said:
You don't mention how the rifle was tested. It is not unusual for a used rifle to accept a No Go gauge.

I believe that the gunsmith used No GO gauage and just told me there was a bit of headspace and not to worry about it.

The rifle was made in 1947 and has had a lot of range use as well as hunting over the years. I think I am comfortable with the "wear" explanation from Triaq and will stop fussing about it.:D
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Headspace will tend to increase with use over time as a result of one or all of the following wear factors; wear on rear surface of bolt lugs, wear or set-back of bolt lug seats in receiver, and wear on bolt face(least likely).
Most sporting rifles don't get enough use to create a headspace problem, altho I've encountered a couple where I think that the problem was due to overly excessive bolt lapping. Military rifles can see extensive use and are therefore more likely to develop increased headspace.
With military pieces like the Lee-Enfield this can generally be corrected by installing a longer bolt head. With a bolt gun,like the M1903 Springfield,a longer or unworn bolt can be substituted. In the case of Garand or M14 types a longer,unworn bolt can normally correct the problem.
In some cases lug seats in the receiver can wear to a point where a new barrel must be installed and headspace established by reaming to a point where the piece will qualify on the appropriate go and no-go headspace gauges. In other cases an existing barrel can also have the shoulder turned down and re-installed a part or full turn to shorten up the headspace.
For your M70 in .30-06. If the rifle closes on the no-go gauge it should be checked with the slightly longer .30-06 field gauge. If it does not accept the field gauge it is good to go. If you are shooting the rifle and not experiencing case head separations, I'd venture to say that you are still OK.
 
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The head space is set when the rifle is made. It may change slightly with wear.

Excessive headspace usually is not a problem with factory ammunition and factory rifles.
If excessive headspace presents a problem it usually is in the form of a case separation. Case separations can be serious as the brass is no longer a seal against 50,000 psi.

Head space becomes a bigger problem with reloaders who do not size the case correctly and in over sizing the case create head clearance. Head space in the rifle and head clearance in the reloaded case can easily cause a case separation.
 
Juster said:
You always have headspace. It isn't a bad thing as such, allowing you to close the bolt easily. If you have too much, it will stress the brass.
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Possibly to case failure, but in this particular rifle I doubt that is the situation. I have never heard of a rifle with dangerously excessive headspace shooting tight groups like this one apparently does.

Supposedly a "gunsmith" even verified the safety of it.

Like I said, if that rifle will shoot 1/2" @ 100 yds. it's a keeper. Anything you do to it will open up your groups.
 
Marcel B. said:
Nice gun, if that rifle will shoot 1/2" at 100 yds. I wouldn't touch a darn thing on it!!!
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Yes it shoots well. In fact it often will punch a couple touching/overlapping and maybe one 1/2 or less away at 100yds with 180 gr Nosler Partitions from Federal. I often think the one that doesn't touch is my personal "failing".Sometimes it will bunch all three right up against each other.
I have no intention of ever "touching" it. She is a grand old lady and I protect and worry about her like she was my Granny!!

Thanks for all the reply's gentlemen. I feel a lot better about the apparently unimportant headspace.:D
 
"...How does excess headspace occur?..." Bolts can get compressed over time too.
Headspace is a rifle manufacturing tolerance that allows any make of like ammo to be used in any like chambered rifle.
"...inconsequential headspace..." Whatever he meant by that. Could be that the bolt was close to closing on a No-Go. That doesn't count. Has to completely close to be bad.
If the bolt closes, completely, on a No-Go, it's not the end of the world. If it closes, completely, on a Field, the headspace is excessive and the rifle isn't safe to shoot with any ammo.
Mind you, if you're not getting any indications of bad headspace(primers backing out, hard bolt opening, flattened primers, etc. Case head separations means extremely bad headspace. Although they can mean poor brass too.), it's likely just fine.
"...unimportant headspace..." Headspace is important. Doesn't sound like your rifle has bad headspace though.
 
Sunray:
Bad headspace is undoubtedly important and consequential but I wasn't actually quoting my gunsmith who is a very good man. Basically he assured me I had nothing to worry about and I'm taking him at his word. We just did not discuss headspace per se nor it's origins or implications in detail and I wanted to know more about it.
Many thanks again to you and the others who helped me out. I fire about a box of ammo per summer and one or two in hunting season if that, so I don't expect any changes in headspace in my lifetime. (I'm healthy but I'm also 66.)
 
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