Headspace - how much is too much ?

E

exomax

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I apologize if this has been asked before, but could not find any info here....

Rifle Headspace : 1.625" (308Win, bolt action)

Reloads : Shoulder pushed back to appx. 1.610" (let's say 13/1000" too far back) (IVI Brass,1F)

I am wondering if the brass can take it without separating ? I normally try to push the shoulder 2-3/1000 back, but these ones were bought and when I measured Headspace, approx. 35% were right around the 1.610" mark, while the rest was basically 2-5/1000" back.

Don't want to run the risk of damaging anything due to separation ? ... is it safe to fire ??

Thx:)
 
exomax said:
I apologize if this has been asked before, but could not find any info here....

Rifle Headspace : 1.625" (308Win, bolt action)

Reloads : Shoulder pushed back to appx. 1.610" (let's say 13/1000" too far back) (IVI Brass,1F)

I am wondering if the brass can take it without separating ? I normally try to push the shoulder 2-3/1000 back, but these ones were bought and when I measured Headspace, approx. 35% were right around the 1.610" mark, while the rest was basically 2-5/1000" back.

Don't want to run the risk of damaging anything due to separation ? ... is it safe to fire ??

Thx:)
Click to expand...

You should be fine. 15 thou, while a little loose, is not likely to cause a case head separation. There is an interesting chapter in Hatcher's Notebook on headspace, where a rifle in 30-06 (likely a 1903 Springfield) had the chamber progressively cut back from 1.9395" (nominal minimum of 1.940" for proper headspace), to 2.0050", a whopping 65 thou, essentially leaving the cartridge to be held against the bolt face only by the extractor. Aside from a decrease in velocity, they had no case head separations reported (from what I can remember).

That aside, the max headspace on a .308 is 1.640" (with min being listed at 1.630"), and the cartridge is listed at 1.634"-0.007", giving a maximum allowable 13 thou between your loosest chamber and your smallest cartridge. 2 thou outside of this won't hurt anything.
 
The problem is the case will stretch to meet the bolt face and cause the case to fail early.

The SAAMI lists headspace as min and max with .010 in between and between the GO and NO-GO gauge is .003 for setting up a new barrel.

If the OP wants the cases to last then the trick is to not let them stretch on the first firing and resize them with minimum shoulder bump.

Meaning .012 to .013 head clearance is beyond the elastic limits of the brass and the case will stretch and thin.

HK76WCp.jpg


sHgqVJR.gif
 
bigedp51 said:
The problem is the case will stretch to meet the bolt face and cause the case to fail early.

The SAAMI lists headspace as min and max with .010 in between and between the GO and NO-GO gauge is .003 for setting up a new barrel.

If the OP wants the cases to last then the trick is to not let them stretch on the first firing and resize them with minimum shoulder bump.

Meaning .012 to .013 head clearance is beyond the elastic limits of the brass and the case will stretch and thin.

{images omitted}
Click to expand...

BigEd, you have an awesome array of drawings, images and animations in you library of knowledge, always much appreciated!

I agree with Ed, A false shoulder is the best solution for the OP. If this were a 303 LE, I would be using an O-ring for the first firing. It's a pity that there is no equivalent "quick fix" for rimless bottlenecks :(
 
bigedp51 said:
The problem is the case will stretch to meet the bolt face and cause the case to fail early.

The SAAMI lists headspace as min and max with .010 in between and between the GO and NO-GO gauge is .003 for setting up a new barrel.

If the OP wants the cases to last then the trick is to not let them stretch on the first firing and resize them with minimum shoulder bump.

Meaning .012 to .013 head clearance is beyond the elastic limits of the brass and the case will stretch and thin.

HK76WCp.jpg


sHgqVJR.gif
Click to expand...

Of course it's harder on the brass, but that's not what the OP asked. He asked if they were safe to fire. The answer to this is yes it is most likely safe and not going to cause any ill effects as the brass is only slightly undersized.

13 thou head clearance is the acceptable maximum for the largest SAAMI spec chamber and the smallest spec brass casing.
 
Thanks guys, learned something !
I wrote headspace, but head clearance is what I meant. 13/1000" is beyond elastic limits and stretching & thinnng will occur. In the end a little loose but within safe limits.....kinda like my old-school grandmother buying shoes for me when I was little....
 
exomax said:
Thanks guys, learned something !
I wrote headspace, but head clearance is what I meant. 13/1000" is beyond elastic limits and stretching & thinnng will occur. In the end a little loose but within safe limits.....kinda like my old-school grandmother buying shoes for me when I was little....
Click to expand...

I have fired .303 British cases in a Enfield rifle with .020 head clearance and nothing happened, "BUT" the cases were tossed in the trash due to stretching and thinning and would have separated on the next firing.

And since you asked the question in the reloading forum and measured the cases I assumed you wanted to reload these short cases.

I have a RCBS case mastering gauge that measures thinning in one thousandths of an inch and why I recommended fire forming your cases if you want to save them for reloading.

jDCS39v.jpg


The sectioned case below is a once fired factory loaded Winchester .303 British case that stretched .009 with the headspace set at .067.

YoV80b4.jpg
 
It's loaded ammo I bought. Loose in a box. Just for fun at the range with the intention to keep the brass and reload.
So far, out of appx 300 tested rounds, 75 are appx 13/1000" "shorter". They are consistently around the 13/1000 mark, so I assume it might be an adjustment issue somewhere in the manufacturing process. The rest of the rounds is within 5/1000". I can live with that. Very few are even up to 2/1000" too long. Might not be able to close the bolt, but that's fine, can work with that. I use a rcbs precision mic to test them.

Looking at the visible thinning with the 9/1000" stretch, I will just toss the cases in question after firing and forget about it. I'll keep my eyes open for one of theses RCBS case mastering gauges. Want one now. :)

I've seen case head separation live and in color at the bench beside me. It was a savage bolt, nothing serious happened, but certainly looked interesting. Don't want to do this to my rifle.

Also, I was wondering if you run a higher risk of the primer pocket leaking with cases that stretch a lot ? Don't want to etch/burn the bolt face.

I don't have semis but wondered what could happen if you would run the cases in question in a 7.62x51 semi. I was told they might have loose chambers and max headspace is different from 308Win.
 
I think your IVI brass is military 7.62x51 and if made like our American Lake City 7.62 brass is harder and thicker in the base. Meaning it was made to be fired in military chambers longer in headspace and larger in diameter. Do your cases have the NATO symbol stamped on the base?

The big question is this factory loaded ammo or did someone reload it?
 
Fired a few today. Nothing happened. Brass looked the same on the outside after firing, only primers backed out a little bit, but did not leak. Accuracy was *&^#&$^%
Precision mic says almost no stretching. Some cases showed cracks in the necks. I assume it is harder and thicker brass. Doesn't matter anymore, it ended up where it belongs...the garbage can. Lesson learned. ....... Hope some poor guy doesn't dig it out again.
 
exomax said:
Fired a few today. Nothing happened. Brass looked the same on the outside after firing, only primers backed out a little bit, but did not leak. Accuracy was *&^#&$^%
Precision mic says almost no stretching. Some cases showed cracks in the necks. I assume it is harder and thicker brass. Doesn't matter anymore, it ended up where it belongs...the garbage can. Lesson learned. ....... Hope some poor guy doesn't dig it out again.
Click to expand...

When the primers back out of the primer pockets it means the chamber pressure was not great enough to push the case to the rear and contact the bolt face.

Example my fired 30-30 cases always have the primer protruding from the base of the case at 38,000 cup or 42,000 psi.

Below a cartridge case firing and showing the primer backing out and then the case stretching to meet the bolt face at higher chamber pressures. The red and yellow areas are the high stress areas with stretching.

This is why .001 to .002 shoulder bump is recommended in a bolt action as this does not exceed the elastic limits of the brass.

Cne2IGF.gif
 
So when I set my re-sizing die so my cases close in the chamber and there is no play and therefore very little head space if any, is this a dangerous thing to do ? If my Federal cases stretch on the average .004-5" per firing, does it mean this is how much head space I must maintain for safety reasons ? I've noticed improved accuracy and consistency when my cases have no play in the chamber but safety first.
 
1-2/1000 shoulder bump is what I aim for when I resize. I only full length resize. 10x fired and it is taken out of circulation. Assuming it is new brass, the same rifle every firing and the shoulder gets pushed back 2/1000" max per full length resizing for a total of 20/1000" over 10 firings, does this mean the web does not thin because the 2/1000" shoulder push back per full length resizing does not exceed the elastic limit of the brass ? (apart from hardening and primer pocket loosening) .....Or is it a more "even" thinning compared to one big strech, lets say 15/1000" in one firing ?

Never seen a protruding primer before. Funny thing ist that a guy at the range I showed some cases said it was overpressure....exactly the opposite :) Not enough pressure to stretch the case enough to push the primer back in. The bolt face also showed brass residue only around the firing pin hole, not where the rim sits.

Well, thanks to the explanations and graphics I learned something new when trying to "read" a case after firing. Thanks to all and especially bigedp51 !

@IMR4320: The way I see and understand it, the less play the better. Less play (Head clearance) translates into better accuracy and longer case life (less stretch).
 
IMR4320 said:
So when I set my re-sizing die so my cases close in the chamber and there is no play and therefore very little head space if any, is this a dangerous thing to do ? If my Federal cases stretch on the average .004-5" per firing, does it mean this is how much head space I must maintain for safety reasons ? I've noticed improved accuracy and consistency when my cases have no play in the chamber but safety first.
Click to expand...

I use a Hornady cartridge case headspace gauge below, I measure the "fired" case and set the die for .001 to .002 shoulder bump for a bolt action and .003 bump for my AR15s.

H0SXHH8.jpg
 
@IMR4320: The way I see and understand it, the less play the better. Less play (Head clearance) translates into better accuracy and longer case life (less stretch).

This is what I kind of thought. Thank you.
 
bigedp51 said:
I use a Hornady cartridge case headspace gauge below, I measure the "fired" case and set the die for .001 to .002 shoulder bump for a bolt action and .003 bump for my AR15s.

H0SXHH8.jpg
Click to expand...

Ok, so basically you set your headspace .001-2" which ensures reliable bolt closure but the case is reasonably firm in the chamber and I understand why AR needs slightly more.
 
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