??? Headspace measurment ???

[sappnasty]

Hello again fellas, I have another question. As I get closer and closer to reloading for my rifle, I am trying to get as much information as I possibly can before I seat that first bullet. When I received my rifle, it came with a large tag (pictured below) with a head space measurement. It states that my specific rifle has been headspaced to 1.632. Now when I was reading my Speer #13 manual it clearly defines headspace as "The distance from that surface of the barrel or chamber that prevents the cartridge from moving farther foward into the chamber to the face of the breech with the action fully closed and locked." Now I understood that as the total measurement of a cartridge right? Problem is, when I measured my .308 Hornady brass with my caliper is measures 2.021??? I looked at the illustration of the cartrige in my manual and it does not display what part of the cartridge is considered in headspace mesurement. I have tried my best to understand this by reading and researching, but I am lost. Can some one please tell me what part of the cartrige is considered in headspacing...or what the total length of my .308 brass should be to fit correctly in my rifle? I have included a picture of the tag sent with my rifle.

 

[243winxb]

Read this http://www.thehighroad.org/showthread.php?t=561001

 

[hdbiker1]

The headspace is measured from the closed bolt face to the datum point, which is a point on the shoulder that is .400 in diameter. Btw, your brass needs trimmed. New brass should be 2.015" for .308. Trim length is 2.005".

 

[USSR]

Yep, sappnasty, you're measuring the total case length, not the headspace length.

Don

 

[MEHavey]

For the M1A, I (and many others) recommend that you not try to finesse headspace at all.

- Stick to a complete full-length resizing to ensure effortless chambering
- Trim after every firing (The M1A ejection cycle really stretches brass.)
- Toss the brass (really, dump it/crush the necks w/ pliers) after 4 loadings.

Cheap insurance.

 

[snuffy]

Here's one way to accurately measure exactly what your rifles headspace is. At least as far as the brass you're using goes.

http://www.midwayusa.com/viewproduct/?productnumber=574297



Or get the Hornady set-up, then you can measure just about any caliber.

http://www.midwayusa.com/viewProduct/default.aspx?productNumber=479704

Another thing, I hope you caliper is zeroed, if so, that brass is stretched a lot. Was it fired in your SA rifle? Brass should only grow a couple thousandths per firing. That's why getting a gauge, then controlling headspace of your loads.

 

[MEHavey]

Snuffy is right-on with bolt actions. The M1A, however, really thrashes its brass. The shoulder is blown forward during high-pressure extraction several (many) thousandths, and stretched to boot. Don't even think about sizing based on fired M1A brass.

Case-in-point:

Today I loaded up 20 rounds of my relative mild "standard" SA M1A load: 168SMK/IMR4895/42.5gr/WWCase/BR2Primer

Headspace meas before firing: 1.629"-1.630" (Stoney Point gauge)
Headspace meas after firing..: 1.333"-1.634"

Sized/Trimmed Length before firing: 2.005"
(Resized) Length after firing.........: 2.008"

Bottom Line: Fully-Resize, Trim, Toss after 4.
(Sleep Well)

 

[MEHavey]

Speaking of headspace implications... be sure to use 'hard' and/or milspec primers able to withstand the "Garand Type" firing pin striking (and dimpling) it on even normal bolt closure.

(Think CCI.)

Also, consider getting/using a primer pocket uniformer to ensure the bottom edges of the pocket are square, and will allow correct--sub-flush--seating each/every time.

(Another "must" with Garand-type actions.)

 

[sappnasty]

Thank you for the info gentlemen. I have finally found a sketch of headspace....so hed space as measured by S/A is from the bolt face to the datum point...correct? My question is, how do you determine case length and bullet depth based on the headspace measurement. What are your steps from a once fired peice of brass to shooting at the range. How are you accurately and safely loading for your M1A? I'm sorry for being such a dunce, sometime I basically have to have it spelled out to undestand it...lol

 

[MEHavey]

My question is, how do you determine case length and bullet depth based on the headspace . . .?

You don't.

FORGET trying to tailor your resized headspace/measurement for the M1A.
Full Length Resize and go from there.

Bullet depth will be that which gives you an Overall Cartridge Length of 2.800" or magazine length -- whichever is shorter.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

What are your steps from a once fired piece of brass to shooting at the range...?

FORGET any measurement from a once-fired piece of M1A brass. Any hope of getting tailored case
dimensions from it to use in reloading is essentially zero because of the extraction effects.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

BEFORE YOU DO ANYTHING:
Step A: Read this manual's Basic Reloading Section(s) five (5) times:
http://www.amazon.com/Lyman-Reloading-Handbook-49th-Edition/dp/B001FBFW6U
STEP B: Read this article five (5) times.
http://www.zediker.com/downloads/14_loading.pdf


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THEN CONSIDER:
Step 1: Lube the case and Full Length resize it.
Step 2: (Optional, but recommend) Clean up the primer pocket with a 'uniformer'
http://www.opticsplanet.net/lyman-primer-pocket-uniformer.html
Step 3: Trim case to ~2.005"/chamfer the mouth
Step 4: Prime case (Using CCI Large Rifle at at this stage)
Step 5: Measure out the recommended amount of (IMR4895 at this stage) powder for the bullet weight being used.
(I also suggest a 150gr Full Metal Jacket or 168 Sierra Match at this stage)
Step 6: Seat bullet

 

[Walkalong]

FORGET trying to tailor your resized headspace/measurement for the M1A.
Full Length Resize and go from there.

Good advise. Buy a Wilson case gauge and set up your sizer to make the brass fit the gauge. Continue to check sized brass each time around to make sure it still fits the gauge. As cases age (get work hardened) they spring back more when sized than new soft brass.

 

[243winxb]

I have finally found a sketch of headspace

All you had to do was click the link in post #2 But i quess thats to much to ask of a "Dunce"

 

[kperk]

Can someone tell me why after firing a cartridge in my M1A and measuring the cartridge for headspace using a hornady headspace gauge, the headspace measures shorter on the cartridge after firing than before firing?
I have the headspace dimensions of 1.632" from Springfield for my rifle.
I'm sizing them to 1.628". After firing, they measure 1.625"
What the heck?

 

[243winxb]

kperk, the cartridge body right behind the shoulder expands outward, pulling the neck/shoulder back. When you full length resize, shoulder/neck move forward. A light loading may do this, maybe not a maximum loading.

 

[kperk]

beautiful. Thanks.
I'm loading 41.5 grains of IMR 4895 and putting a 168 grain Hornady on top of that.
I keep seeing where the shoulder pushes forward, therefore increasing headspace measurements on the cartridge. That's why I'm a little worried about setting up the dies to size to a 1.628" spacing if the actualy chamber is shorter. I can't imagine an M1A chamber being that short, though.
Thanks for you help

 

[Walkalong]

Not unusual. The brass is expanding along the body to fill the chamber as the shoulder is getting moved forward as well. The brass springs back a little which is critical to allowing it to be extracted. (One of the qualities brass has that makes it viable to make cases with)

When you size the brass you squeeze the body down moving the shoulder forward until the die shoulder starts moving it back. Once that happens the body is still being squeezed down while the shoulder is pushed back which causes the O.A.L. of the brass start getting longer. Push it one way it has to go in another.

Welcome to THR

 

[kperk]

I worded that incorrectly. I keep reading where the shoulder should push forward and increase the headspace measurement on the cartridge. All of my measurements have given me shorter headspace readings.
Thanks again