[CSestp]

Okay got another stupid q up. How do I find the headspace on my M1A? Just use a set of calipers or is there a special tool? Please remember that pictures help cure stupid. Thanks guys

[Curator]

A quick and easy way to check the headspace on your M1A with factory ammunition is to use the automobile "plastigauge" material. This is a small plastic "wire" that is inserted betewwn the bolt face and the cartridge head beofre closing the action. Once the bolt is locked, the action is opened and the squished plastigauge wire is compared to a chart on the package to determine the clearance between bolt face and cartridge casehead.

http://i743.photobucket.com/albums/xx80/Dsouthall2/plastigauge.jpg

http://i743.photobucket.com/albums/xx80/Dsouthall2/plastigauge2.jpg

[CSestp]

You sir are a god among men.

After thought: So you just take the OL of your round and add what the plastigauge reads out??

[AK103K]

On cases that have a shoulder, headspace is measured from a point, usually at the mid line of the shoulder, to the base.

They have a set of caliber specific gauges that are made specifically to check headspace. This will give you an idea....

http://www.rifleshootermag.com/2010/09/23/gunsmithing_headspace_0612/


Curator's method is interesting, and I'll have to give it a try. Seems it would at least give you a quick idea as to whats going on.

[bergmen]

Okay got another stupid q up. How do I find the headspace on my M1A? Just use a set of calipers or is there a special tool? Please remember that pictures help cure stupid. Thanks guys

The factory should have a record of this. Mine came with a headspace specification card when I got my Walnut Scout Squad NIB.

Dan

[jr_roosa]

After thought: So you just take the OL of your round and add what the plastigauge reads out??

No. Headspace is completely different from OAL. OAL is measured from the base to tip of the bullet. Headspace is (sort of) measured from the base to a point around halfway up the shoulder. I say sort of because somebody else will chime in that headspace is actually the difference between the distance from base to mid-shoulder and the distance from the bolt face to the corresponding spot in the rifle chamber. The definition doesn't matter because the numbers you care about are:

-How long is the distance from the boltface to the shoulder of my chamber (chamber headspace)?
-Is my sizing die set up to make sure I have enough space between the chamber shoulder and case shoulder so that I get good accuracy, but am not over-stretching the brass when I shoot it?

Excess headspace (or anything that makes a big difference between chamber and case size) results in head separation, which will damage your chamber if you let it happen enough, split your stock and dirty your underwear if you have a really good blowout, and give you the fun experience of figuring out how to get a broken case out of the chamber. (They make a tool for this, called a broken shell extractor, they're cheap and you should have one in your M1A kit since it will save the day if you ever need it)

You need a gadget to measure the headspace of your cases at a minimum. Hornady makes one:

http://www.hornady.com/store/Headspace-Gauge-Bushings/

With a bolt action, all you do is fire a couple of rounds, take the cases, attach the above gauge bushing and adapter onto your calipers, and either take the average size or the maximum size and you now know about what the headspace of your chamber is, since fired brass should be fireformed to the chamber. In reality, you might want to check brass you've fired a couple of times to get it completely fire-formed.

The M1A and Garand won't let you do that. Fired brass out of my Garand is WAY too big to go back in the chamber.

Here is an article on using headspace gauges to check chamber headspace.

http://www.odcmp.org/0309/default.asp?page=M1HEADSPACE

You have to take off the oprod and remove the extractor and ejector from the bolt. I use the same technique with fired brass to measure the chamber. I take my sizing die, back it out a ways, measure the case with the headspace gauge, see if it fits the chamber, size it down a few thousandths, try it again, and repeat until the bolt just barely closes all the way. I repeat this a few times and write down the longest measurements that allow closing, and the shortest ones that don't, and my chamber headspace is somewhere in the middle.

Then I use that number to set up my sizing die so that I am sizing to about 0.002" shorter than the longest case that will allow bolt closure.

Here's another good article.

http://riflemansjournal.blogspot.com/2009/08/reloading-headspace.html

Good luck.

-J.

Postscript:

The plastigauge trick will only tell you the difference between a particular case and your chamber, which is not a very useful number. If you use it with an actual headspace gauge like the ones in the CMP article above, it will tell you your chamber's actual headspace if you add the number to the length of the gauge. The trouble with commercial ammo is that I find it has irregular lengths, and it tends to run short. This is because commercial ammo needs to fit every chamber out there, and they don't care as much about case-to-case consistency as a handloader does.

Match grade commercial ammo would be better, but you'd still want to repeat plastigauge measurement a couple of times and use three or four rounds to get a real number. Also, if you're not reloading, then knowing these numbers doesn't really matter much anyway since there's nothing you can do to change them. If you are checking to see if your chamber is out-of-spec, then you really just need to buy or borrow the .308 Win version of the "GO" and "NO-GO" gauges and use the same procedure as in the Garand article.

[TexasPatriot.308]

if you bought yours new, that info should be on the paperwork provided by Springfield Armory anyway.