Headspace issue

adamsgt

adamsgt

Jerry Adams
Fired my Palma rifle for the first time since I started benchrest, about ten years ago. I was checking the fired brass and noticed that headspace was about .0085 longer than the loaded rounds. I ws shooting both my previous reloads and Federal GM .308. The headspace on my reloads and the Federal GM were the same. Back when I was shooting Palma I didn't know near what I've learned in benchrest and am concerned about this difference. I know I can set my die to compensate for this but is this something to be concerned about? Not sure what the difference between the go and nogo gauges are for .308. Comments anyone?
 
about .003
if you are shooting a reasonable load and
all else is good, it looks like the bbl needs to be set back..just a few thou.
you need to look at all the numbers, not just headspace.
resizing that much every time is going to lead to quick case separation.
just my opinion.
or
maybe you are over sizing your cases.
look at the cartridge specs and see where your ammo is.
factory ammo is typically on the short side, your reloads should not.
 
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adamsgt said:
Fired my Palma rifle for the first time since I started benchrest, about ten years ago. I was checking the fired brass and noticed that headspace was about .0085 longer than the loaded rounds. I ws shooting both my previous reloads and Federal GM .308. The headspace on my reloads and the Federal GM were the same. Back when I was shooting Palma I didn't know near what I've learned in benchrest and am concerned about this difference. I know I can set my die to compensate for this but is this something to be concerned about? Not sure what the difference between the go and nogo gauges are for .308. Comments anyone?
Click to expand...

New brass is generally a few thousandths shorter at the shoulder than SAAMI minimum chamber headspace. You add that to the difference between minimum and maximum headspace and you could come up with the number that you mentioned, depending on the manufacturer. One thing is for sure, back then you had no idea as to how to properly set a FL die :) If you are concerned, buy a no go gauge.
 
Boyd Allen said:
New brass is generally a few thousandths shorter at the shoulder than SAAMI minimum chamber headspace. You add that to the difference between minimum and maximum headspace and you could come up with the number that you mentioned, depending on the manufacturer. One thing is for sure, back then you had no idea as to how to properly set a FL die :) If you are concerned, buy a no go gauge.
Click to expand...

I bought the rifle from Sinclair Intl in 2003. It's a Millennium action. Sinclair had Dwight Scott do the barrel work on all the guns they sold. At some point, for some reason, I decided I needed a new barrel on it. Being ignorant at the time, I had never measured the brass the way I've learned in benchrest. So, I bought a mew barrel and had a friend who does good work, put the new barrel on the gun. However, I never measured the headspace, so I don't know if he might have chambered it a little long. I still have the original barrel that Dwight did and If I can find it I'll try to see what I can glean from it. It could possibly still be a good barrel. Back then I might have blamed the barrel for my failures. Anyway, it was just a bit shocking to see that much difference in the brass since I've learned to turn my 6PPC brass to the tenth and size my brass likewise.
 
Went out to my reloading shed and found a .308 no-go gauge. I didn't strip the bolt but I inserted the gauge and the bolt closed easily. Don't have a field gauge but I'm not going to try that one. So, I guess that barrel needs to come off. It wasn't shooting all that good at 100 yds, about a 2 inch group. I was mainly trying to zero in a Nightforce 15-55 that I'd mounted on the gun. Back to the drawing boards.
 
This is so common in Palma that I'd bet if you asked some old timers they'd remember setting around BS'ing and setting their empties on the table and comparing slant, how much the wobbled.... I swear these guys thing 6-8 thou long is normal!

I stole this image from Laurie's magazine

primers popped up.jpg
 
you can cheat a bit with the go gauge.
add one layer of thin scotch tape to the base,
measure end to end, and try it,
then layer 2 and layer three
it will not be perfect but it will give you an idea
 
Well this is turning into an education

The info on my Forster go gauge shows 1.63 and the no-go shows 1.634. So there is only .004 difference between them. I went to the SAAMI web site and downloaded pdf files of their cartridge specs. They show the Max headspace for .308 as 1.64 and the Min as 1.63. Now it gets interesting. I measured the factory Fed GM .308 and it was 1.62 The fired Fed GM was 1.63. My reloaded Lapua brass .308 is 1.621 and the fired Lapua was .1631. As this reloaded Lapua is about 10 years old (550 rnds) I'm guessing I used the loaded Fed GM to set my sizing die. As both the fired Fed GM and my fired Lapua show about 1.63 there should be no issue with the chamber. So, I guess I can still shoot the old loaded Lapua although not for matches. I'll start working up loads for this rifle with new brass like I've learned to do in benchrest. Also, I measured unfired Lapua .308 brass and the headspace was 1.62 as well. Not sure why the new ammo and brass is set at 1.62. So, with my headspace being at 1.63, how far back should I go on resizing, .003/4 or should I do like 6ppc and do .001/2?
 
leaving out numeric places is not correct.
saami gives both chamber and cartridge numbers.
the intent is that the largest cartridge will always fit in the smallest chamber.
( this is not always true..look at 30'06, or even this...0.004 interference fit at max cartridge and min chamber)
but
the headspace is 1.630 min to 1.640 max.technically this is not the same as 1.63
the largest cartridge is 1.634 down to 1.627( 1.634-.007). again you have the numbers wrong.
separate drawings for chamber and cartridge
what really maters is that you size for YOUR CHAMBER.
it sounds like you sized too small.
decap the fired cases and turn the sizing die up,
turn it down and size brass till you get the fit you want
 
If the ammo shoots without breaking (anything) it probably will shoot as accurately as anything else.
 
retired said:
leaving out numeric places is not correct.
saami gives both chamber and cartridge numbers.
the intent is that the largest cartridge will always fit in the smallest chamber.
( this is not always true..look at 30'06, or even this...0.004 interference fit at max cartridge and min chamber)
but
the headspace is 1.630 min to 1.640 max.technically this is not the same as 1.63
the largest cartridge is 1.634 down to 1.627( 1.634-.007). again you have the numbers wrong.
separate drawings for chamber and cartridge
what really maters is that you size for YOUR CHAMBER.
it sounds like you sized too small.
decap the fired cases and turn the sizing die up,
turn it down and size brass till you get the fit you want
Click to expand...

OK, OK, I freely admit that I am woefully ignorant when it comes to reading these SAAMI diagrams. I am trying to educate myself in this area so I can better understand what was going on in this case. I feel I have a better grasp now but still have much to learn. However I am still curious why Lapua would make their .308 brass with 1.62000 headspace. I guess that's because someone might have a chamber that short.
 
It is not just lapua, essentially everyone does.
They want to ensure it fits, if it is smaller it will always fit a SPEC chamber.
and to get on a soap box, chambers have headspace , brass has
head clearance.

adamsgt said:
OK, OK, I freely admit that I am woefully ignorant when it comes to reading these SAAMI diagrams. I am trying to educate myself in this area so I can better understand what was going on in this case. I feel I have a better grasp now but still have much to learn. However I am still curious why Lapua would make their .308 brass with 1.62000 headspace. I guess that's because someone might have a chamber that short.
Click to expand...
 
retired said:
It is not just lapua, essentially everyone does.
They want to ensure it fits, if it is smaller it will always fit a SPEC chamber.
and to get on a soap box, chambers have headspace , brass has
head clearance.
Click to expand...

Do you ever get a little lonely up on that soap box?
 
.308 vs 7.62 NATO comparisons

This is the comparison chart we did of .308 vs 7.62mm NATO headspace differences. The one thing to notice is that even though the .SAAMI chambr MIN is 1.630", the manufacturing GO is 1.632".
 

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  • 7.62mm-.308 HS Comparison.docx
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what "manufacturing" go gauge ?
not mine.

MilGunsmith said:
This is the comparison chart we did of .308 vs 7.62mm NATO headspace differences. The one thing to notice is that even though the .SAAMI chambr MIN is 1.630", the manufacturing GO is 1.632".
Click to expand...
 
MilGunsmith said:
This is the comparison chart we did of .308 vs 7.62mm NATO headspace differences. The one thing to notice is that even though the .SAAMI chambr MIN is 1.630", the manufacturing GO is 1.632".
Click to expand...

Thanks for the chart. Saved it for reference.
 
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