Proper Headspace For My Garand

[baddarryl]

Hi everyone, I admittedly am going this a little backwards. Well maybe, maybe not:

I am following Glen Zedikers book Top Grade Ammo in which he recommends.004 set back from fired cases for safety in semi autos. So I have unfired cases at 4.060 and fired cases at an average of 4.065 if I use his recommendation I would set the shoulders at 4.061. To me that makes sense.

I have 3questions:
One is it accurate to take the fired case readings from a different brand of case? I don't have any unfired cases as I shot them all up before reading about this so I used to other brands of new cases and they actually were the same at 4.060

Two: I have once fired resized cases of a 3rd brand that measure 4.063, which is obviously .002 more than the .004 recommended at .001. Now he did say .002 or .003 could be ok in a clean chamber which mine is. Do I need to resize these again to get that .004? I also resized before reading about this using the die makers recommended method which is why they came out that way.

Three: And if so do I need to trim again?

Thanks

 

[44 AMP]

At the risk of arguing minutae, heaspace is the space in the rifle measured from one specified point (usually the bolt face) to another specified point in the chamber, and this is different for each different cartridge design. And there is a range of tolerance allowed within which the rifle is "in spec" and outside of which, it is not.

What you are talking about is how to "best" fit your reloads to the rifle's chamber.

Also remember that no matter what an expert says to do, you don't have their gun(s), and yours COULD be different enough to matter.

With the complicated systems of a semi auto rifle, there is more involved in getting the best possible accuracy than just case fit in the chamber.

Question One: not exactly sure what you are asking. Measurement of each fired shows what they are. There will be variances.

Question Two: do you need to resize again? I'd say only if the ammo doesn't chamber correctly. You may WANT to, to try and get the magic number you are looking for, but if it works as is, why would you need to?

Question Three: for the .30-06 max listed case length is 2.494". Recommended trim to length is 2.484". If you are less than the max length you are safe, if you're at the recommended trim to length, its convenient.

I am following Glen Zedikers book Top Grade Ammo in which he recommends.004 set back from fired cases for safety in semi autos. So I have unfired cases at 4.060 and fired cases at an average of 4.065 if I use his recommendation I would set the shoulders at 4.061. To me that makes sense.

Could you please provide some additional explanation of how you are measuring (from where to where?) because .30-06 length numbers beginning with "4" don't make sense to me.

 

[baddarryl]

At the risk of arguing minutae, heaspace is the space in the rifle measured from one specified point (usually the bolt face) to another specified point in the chamber, and this is different for each different cartridge design. And there is a range of tolerance allowed within which the rifle is "in spec" and outside of which, it is not.

What you are talking about is how to "best" fit your reloads to the rifle's chamber.

Also remember that no matter what an expert says to do, you don't have their gun(s), and yours COULD be different enough to matter.

With the complicated systems of a semi auto rifle, there is more involved in getting the best possible accuracy than just case fit in the chamber.

Question One: not exactly sure what you are asking. Measurement of each fired shows what they are. There will be variances.

I am asking if i set the shoulders back enough in relation to the fired cases. All my numbers are averages.

Question Two: do you need to resize again? I'd say only if the ammo doesn't chamber correctly. You may WANT to, to try and get the magic number you are looking for, but if it works as is, why would you need to?

Ok. I'll try that.

Question Three: for the .30-06 max listed case length is 2.494". Recommended trim to length is 2.484". If you are less than the max length you are safe, if you're at the recommended trim to length, its convenient.

I trimmed to 2.484 after initial re sizing.



Could you please provide some additional explanation of how you are measuring (from where to where?) because .30-06 length numbers beginning with "4" don't make sense to me.

Using Hornady Headspace gauge so the added length is from the gauge

Thank you!

 

[44 AMP]

Using Hornady Headspace gauge so the added length is from the gauge

Ok, that explains why the numbers are what they are. It does not, however provide any frame of reference for people who aren't using that gauge.

You're asking questions about very small things and if they matter, and in order to give the best answers I can, I need to understand what you are doing, rather precisely. There are a lot of details that, if misunderstood will result in incorrect advice.

I haven't read the book your reference so no idea what he said, or why, Though from the title he has a specific goal and point of view.

This, in particular, intrigued me...

he recommends.004 set back from fired cases for safety in semi autos.

What it says is obvious enough, but what does it actually mean, as in where does it apply and how?

What is the shoulder set back from FL resizing, compared to his recommendation of .004"?

and just what does he mean by "safety"?? is he talking about preventing a slam fire?? Failure to lock up? something else? did you get any of that from what you read??

The M1 Garand has a floating firing pin, it is supposed to bounce LIGHTLY off the primer when the bolt closes. Cases are not fed up under the extractor (like a Mauser bolt action's or the 1911A1 pistol.) Cases come out of the clip and are pushed into the chamber until they stop, then the last bit of bolt forward movement locks the action shut and snaps the extractor over the case rim at the same time.

Cases too short (case base to shoulder datum point) could go too deeply into the chamber. Cases too long could prevent full proper lock up, and cases extremely too long could keep the action from locking up at all.

With the rifle in proper working order and things still in spec, the design prevents the firing pin from hitting the primer until the bolt is fully shut.

However, there are very few new Garands, and its not impossible that the older WWII/Korea guns might be worn to the point where they work properly when the ammo is in spec, but might not provide the designed safety factor when something is not.

Out of battery firing should not happen, but since it has, then obviously, it can.

if I can confuse things further, don't be afraid to ask!

 

[HiBC]

I think this conversation is about "Head Clearance" Headspace is about the gun. Head clearance is about how the ammo fits the gun.When the case is forward, stopped against the shoulder, its the space between the breech face and the case head. "Head Clearance".

Both Mr Z and Precision Shooting's Guide for reloading for Competition stress M-1 and M-14 rifles ammo should have a specified "Head Clearance" when loaded.

The OP says Mr Z recommended .004. I'll take his word for it.

With bolt action rifles we like .002 head clearance. It makes brass last longer and the hand on the bolt handle assures full battery lockup.

The M-1 and M-14 rely on the op rod spring for full battery lockup.

The .004 clearance facilitates reliable full lockup. With the right tolerance stackup these guns can fire in a "Not quite full battery " condition.

You do have to be careful assuming your fired brass represents baseline zero head clearance. Sometimes they stretch. I suppose if you have the tool and are confident in your ability to strip and reassemble the bolt without losing flying plunger parts you could check your fired brass.
When you have a brass you are satisfied is base line zero head clearance fired brass, save it in your die box.

Using that piece of brass zero your Hornady tool or RCBS Precision Mic or whatever comparator system you have to that brass. Then setup your sizing die in the press to show .004 shorter,or"head clearance" after sizing a different piece of brass.. You are measuring the change from sizing.

Your rifle will remain consistent ,pretty much.

Brand to brand,or how work hardened it is, brass may vary in "springback"

Monitor and adjust as necessary. For example,Lake City,WW and Federal may vary in head clearance after sizing. Sorting can be helpful.

Thats one perfectly acceptable method.

A variation I use is with a Wilson bushing type case gage. The gauge stays the same. Its a lot like a chamber. It has a step ground in it for min/max to size to SAAMI spec length. That tells you the ammo is pass/fail. Instead , Once you determine your base line zero head clearance length, you can just drop your brass in the bushing guage and measure over the case in the guage,assembled. The gauge itself plus the number you write inside your diebox, (which would be the measurement that gives you .004 head clearance) becomes your standard.Set your sizing die to that.

You will get some case stretch. Monitor for "stretch rings" with the paper clip trick. See what you get,but I would not expect many more than 4 reloadings
Unless you have Lapua brass

 

[mehavey]

1. You want guaranteed full lockup w/ a Garand. The consequences of less than that are "very unpleasant" -- particularly w/ that action

2. Brass is cheap. Eyes and hands are not.

3. Unfired/commercial rounds are your best "Fail-Safe" measure of minimum cartridge headspace dimension to ensure full lock-up

4. Hornady headspace comparator will give you a benchmark datapoint for that dimension

5. Size to that dimension -- checking w/ the comparator as you go.

6. Periodically paper-clip test case batches as you reload.

7. Remember #2

 

[akinswi]

baddarryl,

If your using a LE wilson gauge. I found my M1 actually both my M1s shoot the most accurate at the bottom step.

And I tried several different methods and hundreds of groups and How I came to this is I found that new cases usually sit at this bottom step. Even after running them thru a resizing die.

So I carbon copied that . Measure a new case see where it lands on your shoulder bump, then measure your fired case. Then adjust your die to match the new case.

If your annealing after firing, you may want to readjust your die because it will set the shoulder back farther than you may want.

One thing I did was stop using different brands of brass it was maddening trying to figure out shoulder bumps powder charges etc

Stick with 1 brand of brass I promise you it will make it easier. I finally bit the bullet and bought 1000 cases of the same brand .

Another thing Bart B and Unclenick, HiBC all the highpower shooters, will mention is that New brass will give you the best accuracy. Practice with your fired cases and new brass for matches if your doing that.

Bottom line is your M1 may like something different but size it to to the bottom step and you should be good to go.

As far as too trimming, just measure the cases and see if they need trimming. I trim 2.485 because thats what sierra recommends but its not set in stone

 

[baddarryl]

Thanks everyone. I think after reading all of this I am going to resize the same brass to get that .004 just to be safe. I feel confident in my calculations. If I have to re trim oh well.

As far as using the same brass my first batch was Greek HXP and the second S&B. I have done the work we are talking about on the S&B. Seeing as how that is more available than the the XHP I am think I will standardize with that.

This still begs the question, are all commercial brass set to the same datum line per Sammi specs when new? For that matter was the old surplus stuff?

 

[akinswi]

The M1 chews up brass pretty good, so once your thru with the HXP brass start stocking up on your favorite commercial brass. Just work up a load for your new lot of brass.

 

[mehavey]

...going to resize the same brass to get that .004 just to be safe.

What are you using for reference point to subtract the 0.004" from?

Unlike a bolt action, Garand extracts under pressure.
The fired case may/may-not represent the chamber.
(Unless you fire w/o the gas plug and then manually extract.)

Even if so, I suggest 5-8 cases w/ a comparator and average the Headspace dimension

 

[baddarryl]

I'll up load pics of what I read in a moment.

 

[HiBC]

Unlike a bolt action, Garand extracts under pressure.
The fired case may/may-not represent the chamber.
(Unless you fire w/o the gas plug and then manually extract.)

That is something to be aware of.

If the bolt will go to full battery without resistance on a piece of fired brass,the brass is not stretched over length. I'd go for the .004.

But to do that gently enough to not distort the brass, I'd strip the bolt. I have experience and confidence stripping and assembling the bolt.

For a newbie,there is the spring loaded extractor detent plunger and the spring loaded ejector to be concerned with. They fly far and are not easy to find.

But with the stripped bolt ,you can have some "feel"

 

[44 AMP]

am not sure about the GI cleaning kits for the M1, but I know the kit for the M14 has the tool for stripping the bolt. Its the funny looking "handle" for the cleaning rods. That handle is a combination tool for several jobs.

One end is made to fit the bolt face, and it compresses the ejector (so you can drive out the pin) and when you twist the tool the right way, it will lift up the extractor so its no longer under spring tension and can be removed.

Only takes three or four hands to do it , and you do need to be sure small parts don't get launched, but generations of GIs and civilian owners have been doing it, so its not impossible, once you learn the tricks.

 

[Unclenick]

To get a measurement off the Garand case that is close to your actual chamber size, remove the gas cylinder plug. The gun will still load normally, but it won't cycle when you fire it because the gas coming out of the gas port just blows out forward. This lets the chamber pressure come down to atmospheric pressure with the case still in place. Then you extract and eject the fired case onto a soft towel or similar surface manually to cool. It prevents the stretching due to chamber grip by residual pressure during extraction. It also prevents the extractor from tending to bend the rim out a little if the load is at all warm. It prevents denting from impact with the gun or the ground upon ejection.

Once you have that measurement recorded, you can figure your case will have sprung back a little. It will probably be no more than a couple of thousandths, but it can vary that much from case to case, so it is best to go the next mile and figure out how much it sprang back. To find out, start as HiBC suggested and strip the bolt. Cut some roughly head-diameter (or slightly smaller) discs of 0.001" shim stock and see how many layers you need to stack up before there is interference. Use slow, gentle rotation of the bolt with your thumb on the op-rod's lug extension to just detect the case shoulder making contact with the chamber shoulder. The locking lug's helical engagement gives you a lot of mechanical advantage, so feeling that contact without jamming and compressing the case to expand outward takes a delicate touch.

 

[Bart B.]

I knew Springfield Armory used a Fastax camera in the 1950's taking high-speed movies of semiauto rifles timing their functions. Took a while, but I found it. Test bullets' distance from the muzzle when the op rod dwell time (no movement) ended and it started moving back were a bit over 4 feet with the M1; a bit over 6 feet with the M14.

Here's the meat of it......

The unlocking cycle of the M1 Garand and M14 rifles was tested in 1957 by Springfield Armory. The purpose of the test was to determine the average time (in milliseconds) from firing pin contact to:

a. Bullet passing the gas port
b. Bullet exit
c. Initiation of operating rod recoil
d. End of operating rod dwell
e. Completion of bolt unlocking
f. Position of bullet at initiation of operating rod recoil
g. Position of bullet at end of operating rod dwell
h. Position of bullet at completion of bolt unlocking

Three single rounds were fired from each of three M1 and three M14 (T44E4) rifles. The ammunition used was M2 AP for the M1 rifles and armor piercing (T93E1 or T93E2) cartridges for the M14 rifles. Each rifle was fully loaded for each series of three shots. High speed motion picture cameras (operating at 6,000 to 7,000 frames per second; about 1 frame every .015 millisecond) and flash strobes were used to record hammer fall, bullet exit, operating rod movement and bolt unlocking during each firing sequence. Lumiline screens were used to record average bullet velocity at a distance of 53 feet forward of the muzzle. The film was analyzed to obtain the data below. Average values were computed from the high speed film as follows:

Data Item ..........................................................M1 Rifle ..............................M14 Rifle
Type of gas system .............................................gas impingement ...................gas cut-off and expansion
Location of gas port from muzzle ..........................1.5 “ .....................................8.0 “
Gas port diameter ...............................................0.0793 “ ................................0.0768 “
Barrel length ......................................................24 “ ......................................22 “
End of hammer fall ..............................................0 milliseconds ........................0 milliseconds
Bullet passes gas port .......................................1.31 milliseconds ...................1.01 milliseconds
Bullet clears muzzle ...........................................1.36 milliseconds ...................1.25 milliseconds
Initiation of operating rod recoil ...........................1.58 milliseconds ...................1.53 milliseconds
End of operating rod dwell ...................................2.89 milliseconds ..................3.57 milliseconds
Completion of bolt unlocking ...............................4.07 milliseconds ..................5.00 milliseconds
Amount of bullet travel at start of op rod recoil ......7.2 “ past the muzzle .............9.2 “ past the muzzle
Position of bullet at end of op rod dwell .............50.2 “ past the muzzle ..........76.1 “ past the muzzle
Position of bullet at completion of bolt unlocking .....88.9 “ past the muzzle ...........123.0 “ past the muzzle
Average bullet velocity ........................................2735 feet per second .............2733 feet per second

Reference: Springfield Armory Technical Note SA-TN11-1094 dated 16 Dec 1957

 

[akinswi]

Bart B,

Is there a link to the actual video out there ? Be interesting to watch

 

[Jim Watson]

Has that test been done with M16?