headspacing?

[kalidro]

I heard of the term the other day at my local gun store
what does it mean? also what are go/nogo gauges for?

i thought this forum may be the appropriate page to ask such
questions.

[1006587]

Here are the basics. A chamber is sized to a certain dimension. A case is sized to a certain dimension. Headspace is the length of a chamber taken from a very specific point in the chamber to the bolt face. If this distance is too long the brass will strech too much and rupture. If the chamber is too short the case won't go in the chamber. Tight or loose headspace will also affect accuracy to some extent.

Go and No-go gages are used to determine if the length of the chamber to bolt relationship is within specs. The bolt should close completely on a Go gage but should not close on a No-Go. This is when the rifle is new. A Field gage is used to determine if a chamber is at the maximum design length. These are usually for old guns that have been fired a lot.

As a rifle wears from use, the headspace will get larger.

Does that answer your questions?

[kalidro]

thanks for the info, but still a little deep for me. may have to read it couple times

[1006587]

Headspace (HS) is SET when the rifle is built. HS is CHECKED after the rifle is in service. How HS is set depends on the type of action. Bolt action, by cutting the chamber after the bolt is fitted, usually. FAL, by changing the size of the locking shoulder. AK, by the depth the barrel is pressed in the trunion. The headspace gage looks a little bit like a cartrige without a bullet. It is inserted in the chamber and you attempt to close the bolt on it. Look here for a picture http://www.midwayusa.com/rewriteaproduct/196171.

How do you check headspace? Strip you rifle. Remove the extractor because it can rub on the gage and fool you into thinking the HS is ok. Clean the chamber. Insert the HS gage in the chamber and GENTLY close the bolt. The bolt should lock up with little of no resistance on a Go gage. Next you grab your No-Go gage and insert it into the chamber. The bolt can start to rotate closed on this gage but should not close all of the way. If it closes on the No-Go, you need to check it with a Field gage. A Field gage is the largest HS that the rifle can be used safely. All of this is done gently so that you don't damage the gages. They are precision instuments and should be used gently.

Go back to the gunshop and see it the gunsmith will show you what he is doing when he checks the HS. It's very simple and takes about 10 seconds to do.

[kalidro]

Thanks 1006587 :)
that really gave me a better pic of what HS is about
i have always been curious about thing and most people
i ask things about never give me such indepth answer
i like this forum :)

[Packrat]

To add some more on the theory, If your headspace is too short the bolt won't close and lock on a cartridge. Most actions are built so that if the bolt doesn't lock, the firearm won't fire, but there are some that will. This is "firing out of battery", and is dangerous--it can damage or destroy the firearm and/or the shooter. The tighter the headspace (as long as it will chamber a cartridge) the more accurate a firearm is (usually), but also the more likely you are to have a problem, especially with dirty or corroded ammunition. This is important for military weapons, especially those used under harsh conditions. On the other end, if the headspace is too great the pressure in the cartridge when it fires will try to shoot the entire upper part of the cartridge out like the bullet. The front of the chamber will stop it, but maybe not in time. This is called a case separation, and again, can damage the firearm and/or the shooter when the case rips apart and the propellant gasses shoot out around the head of the case and the bolt.

AKs are designed to use loose tolerances, because they are intended to be used in combat under harsh conditions. In addition, they were designed to use steel-cased ammunition, which is stronger than the brass-cased ammunition most firearms are designed to use. Unfortunately, this tends to make them less accurate. Since the AK was designed for combat, 95% of the shots in combat are at 200 yds or less, and any AK can hit a man-sized target at 200 yds, this was not a consideration for the designer and most of the users of the AK, including a lot of US soldiers who have faced the AK and then were given a chance to use captured weapons.

The AK is the only firearm I have felt comfortable using a cartridge to set headspacing for. And that's only after working with firearms most of my life, and AKs for the last 10 years.

[kalidro]

so if the HS is a no go what would you have to do?
press the barrel out?(on a ak)
generally you would not have to HS on the AMD 63 right?
or any parts kit

[CAMPYBOB]

if the headspace is too short, the bolt lugs can be fitted by means of material removal...usually a lapping (removing .001" or less) or grinding operations.

the bolt face can also be ground.

the method chosen is usually dictated by the equipment/tooling available.

[Packrat]

And if you don't have the equipment to work on the bolt, yes, you can press the barrel out slightly, and maybe have to press it in again. If you can't get it by then, give up and have someone else do it.