Headspace - What the heck is it?


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Werewolf
February 16, 2005, 12:03 PM
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I remember in Army Basic way back 34 years ago them telling us about setting headspace and timing on the M2 .50 cal but since I was gonna be a tanker I pretty much ignored the demonstration and the .50's we had on our M-60 tanks we didn't have to worry about that stuff.

Now I see headspace mentioned very frequently here and how if it's off nasty things can happen. I see that it is measured in different ways and from different points depending on the cartridge.

So could someone who is knowledgeable please provide an explanation of what headspace is, what it does and the ramifications of it being wrong.

Inquiring minds wanna know...

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musher
February 16, 2005, 01:38 PM
heh heh, do a search and you'll get all kinds of entertaining reading about headspace.

If I had to define it off the cuff I'd say it is the distance measured from the face of the closed breech to a datum on the specific cartridge you're working with. That datum varies from cartridge to cartridge, and could be the middle of the shoulder, rim of the cartridge, the belt, the rim or ...??

Measurement on a particular gun is done using precisely machined gauges (headspace gauges). They come in a bunch of different varieties for each cartridge, but your basics are go and no go. Simplified, if the bolt will close on a go but not on a no go gauge, your headspace is within specs. Some guns require removal of things like extractors from the bolt to get a good measurement.

Headspace is there, because we need a little slop in the machine for cartridges to move in and out of the chamber w/o undue friction. Too little headspace, and you'll have problems closing the bolt on some cartridges.

Too much headspace allows the brass to expand more than designed. In severe cases, it may rupture, venting gases back into the action.

I probably got a lot of this wrong, but I think the basics are correct and sooner or later, someone will wander by to correct my errors.

Mr. Mysterious
February 16, 2005, 01:46 PM
This seems to be a pretty good article...

http://www.surplusrifle.com/shooting/headspace/index.asp

Werewolf
February 16, 2005, 02:47 PM
Thanks guys. One is never too old to learn something new.

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