most what's the most commom cause of excessive m1 headspace?

[goo]

chamber, bolt or receiver?
i'm guessing if its the receiver, not much can be done if a different bolt don't help.. don't know.
10-q,
goo

Information

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[Dan Shapiro]

"Most common cause of excessive headspace"? Barrels do 'wear out'. Extended periods of rapid fire will do this more quickly. Yeah, there are gauges to measure the receiver, and they can 'stretch' over time, but we're talking 'most common cause'.

[Devil Dog]

This is just my opinion and I have no studies or facts to back it up.
I think the three areas that control headspace will wear in this order: Receiver lugs, Bolt lugs, Barrel Chamber.

[AKA Hugh Uno]

This is just my opinion and I have no studies or facts to back it up.
I think the three areas that control headspace will wear in this order: Receiver lugs, Bolt lugs, Barrel Chamber.

Mr. Devil Dog is correct. Barrel THROATS wear forward from hot gas EROSION, but this has nothing to do with headspace.

[Bill Hollinger]

And I say barrel chamber, bolt, then receiver.

It is not uncommon to go through a couple of WRA bolts to find acceptable head spacing.

[Cosine26]

The M1 Rifle is just another piece of machinery and wears accordingly no matter how well lubricated.
Designed correctly the Bolt should wear first. It requires the least amount of metal and only requires 35 machining operations when compared to the Receiver which takes more metal and requires 81 machining operations. The Bolt is also the easiest to replace. Now what the actual wear pattern is, I don’t know.
I do not see how the barrel could contribute much to headspace. I can only imagine slight wear during the operating cycle and feel that the bore would erode much faster than any wear effect.
JMHO

[latigo 1]

A lot of people confuse throat erosion with headspace wear. Barrels wear out from throat erosion caused by the hot gases from the fired cartridge. This wear occurs at the end of the casing as the bullet is forced out by the expanding gases. Headspace is measured at the shoulder of the cartridge, about 1/2" to the rear of where the hot gases escape. There are no hot gases in this area and the only stress on the shoulder of the barrel is when the soft brass case expands against it. This wear is so minimal that once the barrel is reamed for proper headspace when new, it seldom changes enough to measure. Wear to the area where the bolt lugs rotate against the receiver is what causes headspace to increase.

[dryheat]

http://img.photobucket.com/albums/v6...imroad-hra.jpg
Here is a picture of a bolt of mine that I labeled with the dimensions I found. This bolt was .003 "shorter" than another and that made the difference between passing the field or not. It's the distance labeled "face to back of lug (.613) that was not enough to keep the bolt far enough forward to pass the gauge test.

[dryheat]

Bolt 1(very little finish)

D28287-12 D28287-12
011A() S11-()

OAL( base to rim)____3.797 OAL________3.797

Rim to face__________.110

Face to Lug__________.613


Bolt 2

6528287
US2

OAL(base to rim)_____3.804 (.007 longer than Bolt 1

Rim to face___________.111

Face to Lug___________.616 (.003 longer than Bolt 1

Bolt 1 closes on the field gauge on the HRA receiver
Bolt 2 does not close on the field gauge, but does close on NO-GO

* .003 is a VERY thin sheet of typing paper.

1. A rough measurement can be made by measuring from the bottom-rear of the lug to the rim, then inside from the top-edge of the rim to the boltface and subtracting this from the first measurement

2. The easy way is to simple measure the head space in a given rifle using the different bolts. The military had a bolt gage specifically designed to measure the location of the locking lugs. It was used mostly at depot level and not a common gage.

The critical areas to be measured are the bolt face in relation to the recoil surfaces of the lugs. This is a difficult area to measure due to the helical design of the lug. They are cut at an angle. The measurement would have to be made at a specific location on the lugs. It requires very precise measuring tools, but it could be done on a surface plate and a dial indicator.

I'd stick with headspace gauges myself.

[mhb]

which affect headspace in the M1 (or any locked-breech rifle) are the rear faces of the locking lugs of the bolt and the corresponding supporting surfaces in the receiver. Both of these are subject to mechanical wear (and about equally so, since they are of similar size and their bearing surfaces are intentionally sized to match), and both can be deformed by excessive stress. In service, with good and consistent ammunition, the usual cause of dimensional changes in these parts is abrasion caused by continued use under field conditions of dust and dirt. Both parts are gauged in rebuild, and, if found to be within the specified tolerances, and not otherwise obviously damaged, are judged suitable for re-use. While the chamber of the barrel can be deformed by excessive pressures, it is not normally worn out-of-tolerance by abrasion of the shoulder against which the cartridge case headspaces, and is commonly replaced because of normal erosion in the throat due to long use and/or muzzle damage - though corrosion of the bore due to neglect can cause the barrel to be condemned.
mhb - Mike