.308 Headspace

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johnk
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.308 Headspace

#1 Postby johnk » Tue Sep 19, 2017 9:35 pm

If I understand the SAAMI diagram correctly, headspace is measured at a notional point on the shoulder where it is .400" diameter, the acceptable range at that point being 1.630-1.640". A matching case/cartridge should measure 1.627-1.634", eg:

http://forums.thecmp.org/showthread.php?t=146769

I wouldn't have any immediate interest in this issue except:

    Philip has had issues with primer strike/primer recently
    I have 400 or so virgin Lapua Palma cases I need to prep for use up to the Stawell Match Rifle events in November.
Now, scuttlebutt tells us that new brass is undersized, and for one who uses Wilson gear to bevel necks, I know that new brass fits the Wilson trim die a lot less snug than brass fired in my rifle. Diameter wise that is demonstrably the case. However, measured at .400" on the case shoulder with my Stoney Point gear using a Mitutoya dial verniers, new brass measures exactly the same as rounds I have fired.

As Peter Smith's contemporary was wont to say, "How can this be?" Is the new brass acceptably dimensioned for my chamber?

mike H
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Joined: Mon May 08, 2006 5:34 pm
Location: JUNEE NSW

Re: .308 Headspace

#2 Postby mike H » Tue Sep 19, 2017 11:15 pm

John,
I to have been troubled by this conflict of measurement.The first thing I will ask you,saying that you measured with a Stoney point device,is the thing actually 0.400"?,mine isn't and I get measurements more like 1.617"to 1.618"" depending on the barrel.The new Lapua blue box case I measured today are 1.615""mostly down to 1.613",so about 2 to 3 thou in most cases.I have fired nearly 400 new Lapua cases in my latest FTR rifle without any misfires or trouble.Primers being Federal GM 210 M and CCI Br-4's and Murom KVB small rifle magnum.
Today I loaded 50 new LR Lapua with CCI-200's for club use and to fire form,some pulled 185 grain Juggernaughts and modest loads.I do not expect any problems and I am sure you won't as well.Life was simpler before this obsession with measuring everything you can get your hands on.
Mike.

Gyro
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Location: New Zealand

Re: .308 Headspace

#3 Postby Gyro » Wed Sep 20, 2017 4:22 am

Johnk, the only number u mention that matters here is .400". Whether that measurement means ANYTHING is another story.

Headspace is for all intents and purposes just a NOMINAL measurement. The reloader manages that measurement. I could write a hell of a lot more here but my head still hurts after reading the other thread.

I do all my own machining for my rifles including lots of other wierd innovative stuff so I do understand headspace.

As with LOTS of information/theories in this game all ya can do is get your head PROPERLY around the concepts, the salient points .....

I say TAKE THE FIREFORMING STEP SERIOUSLY then ya can happily forget about that part of the prep and as long as you dont create headspace in your cases by forcing the case too far into the FLS die then all is well with the world and your mind will be free to pay attention to all the other stuff.

BTW I jam all my bullets and dont run an ejector so I don't have a separate fire forming step and bugger me cases straight out of the box with just a minimum scim off the case neck OD to uniform it shoot just fine !!!

Pommy Chris
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Re: .308 Headspace

#4 Postby Pommy Chris » Wed Sep 20, 2017 7:39 am

Simplest way to see if a case has headspace in a given chamber is make up a 2 thou shim and put it on the bolt face then clip the base of the unfired case onto the bolt and insert the case shim and bolt into the chamber. This is done like this so the shim does not fall off. If the bolt is firm to close then you have 2 thou or less headspace if it is easy to close then you have 2 thou or more. If more repeat with another shim added and another until bolt wont close or is stiff to close. I had one shooter who had issues ages ago and I had about 8 shims in there so clearly headspace was his issue. With shims in though dont pull the trigger or the firing pin buggers all your shims up. I usually have shims in my gun box just for this test. Another check you can do is ensure primer is seated enough ie all the way in the pocket. If not the firing pin looses strike energy pushing the primer forward the primer is not seated all the way in.
The shim test is rough and ready as cases have some spring, but if you have 4 though of shim and you just get resistance ie about 4 thou headspace rounds should be going off, more I would be starting to be blaming headspace as a possible issue. Most saami chambers with lapua brass (palma) are 2-4 thou that I have measured in this way.
If chamber is saami specs lapua brass should not give headspace issues ie prevent round going off.
Chris

Gyro
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Re: .308 Headspace

#5 Postby Gyro » Wed Sep 20, 2017 8:30 am

U must have lots more patience than me Chris : I don't carry shims, I just have a big stick to wack the shooter for not properly attending to the basics !

Pommy Chris
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Re: .308 Headspace

#6 Postby Pommy Chris » Wed Sep 20, 2017 8:36 am

Gyro wrote:U must have lots more patience than me Chris : I don't carry shims, I just have a big stick to wack the shooter for not properly attending to the basics !

:lol: That works too :D
Chris

GSells
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Re: .308 Headspace

#7 Postby GSells » Wed Sep 20, 2017 7:27 pm

Pommy Chris wrote:Simplest way to see if a case has headspace in a given chamber is make up a 2 thou shim and put it on the bolt face then clip the base of the unfired case onto the bolt and insert the case shim and bolt into the chamber. This is done like this so the shim does not fall off. If the bolt is firm to close then you have 2 thou or less headspace if it is easy to close then you have 2 thou or more. If more repeat with another shim added and another until bolt wont close or is stiff to close. I had one shooter who had issues ages ago and I had about 8 shims in there so clearly headspace was his issue. With shims in though dont pull the trigger or the firing pin buggers all your shims up. I usually have shims in my gun box just for this test. Another check you can do is ensure primer is seated enough ie all the way in the pocket. If not the firing pin looses strike energy pushing the primer forward the primer is not seated all the way in.
The shim test is rough and ready as cases have some spring, but if you have 4 though of shim and you just get resistance ie about 4 thou headspace rounds should be going off, more I would be starting to be blaming headspace as a possible issue. Most saami chambers with lapua brass (palma) are 2-4 thou that I have measured in this way.
If chamber is saami specs lapua brass should not give headspace issues ie prevent round going off.
Chris

The shim idea is a good one ! But if one doesn't have access to shims , one could use a piece of celo tape , which is approximately 2 thou .

I still haven't figured why I've had troubles with the 280 ackley with correct head space ! Starting out with 30-06 brass and not knowing what to do , was the main cause of the problem .
But I had an odd one not go off and when I got home , checked the head space with the firing pin out and was correct but still that case didn't fire !!??
I've put the 280 Ai on the back burner for now , but suspect something is going on with the primer pocket not being square . I'm using Cci primers and in the .284 or 7-08 Ai no miss fires !!???

Pommy Chris
Posts: 441
Joined: Tue Oct 21, 2014 12:05 pm

Re: .308 Headspace

#8 Postby Pommy Chris » Thu Sep 21, 2017 5:42 am

GSells wrote:
Pommy Chris wrote:Simplest way to see if a case has headspace in a given chamber is make up a 2 thou shim and put it on the bolt face then clip the base of the unfired case onto the bolt and insert the case shim and bolt into the chamber. This is done like this so the shim does not fall off. If the bolt is firm to close then you have 2 thou or less headspace if it is easy to close then you have 2 thou or more. If more repeat with another shim added and another until bolt wont close or is stiff to close. I had one shooter who had issues ages ago and I had about 8 shims in there so clearly headspace was his issue. With shims in though dont pull the trigger or the firing pin buggers all your shims up. I usually have shims in my gun box just for this test. Another check you can do is ensure primer is seated enough ie all the way in the pocket. If not the firing pin looses strike energy pushing the primer forward the primer is not seated all the way in.
The shim test is rough and ready as cases have some spring, but if you have 4 though of shim and you just get resistance ie about 4 thou headspace rounds should be going off, more I would be starting to be blaming headspace as a possible issue. Most saami chambers with lapua brass (palma) are 2-4 thou that I have measured in this way.
If chamber is saami specs lapua brass should not give headspace issues ie prevent round going off.
Chris

The shim idea is a good one ! But if one doesn't have access to shims , one could use a piece of celo tape , which is approximately 2 thou .

I still haven't figured why I've had troubles with the 280 ackley with correct head space ! Starting out with 30-06 brass and not knowing what to do , was the main cause of the problem .
But I had an odd one not go off and when I got home , checked the head space with the firing pin out and was correct but still that case didn't fire !!??
I've put the 280 Ai on the back burner for now , but suspect something is going on with the primer pocket not being square . I'm using Cci primers and in the .284 or 7-08 Ai no miss fires !!???

Supercheap and similar with sell packets of bronze shim sheets with various sizes inside. Using scissors I cut the 2 thou sheets to fit the bolt face.
Chris

pjifl
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Location: Innisfail, Far North QLD.

Re: .308 Headspace

#9 Postby pjifl » Thu Sep 21, 2017 12:12 pm

There are a whole pile of common items you cam make shims from.

Scissors and Soft drink cans are always available whose wall is about 4 - 5 thou thick. Check with micrometer.

Plain paper is about 3 thou thick.

These are more for emergency use and are fiddly but are quite successful.
Best held with a dab of grease on boltface with a cartridge clipped under the extractor before inserting bolt.

Beware these can sometimes get 'lost' inside the locking lug space and become a real problem to clear.
Another potential problem. You do not want creases in the shim material.

The most useful thing is a small 'gauge' made using your chamber reamer to be used with Calipers so comparing fired and sized cases. The chamber reamer is only used deep enough to produce a funnel shape matching your shoulder. Very quick to use to check a select number of resized cases. Usually best to use a slightly oversized drill to open out the neck part of the gauge so there is never a chance of jamming. Also, never take the reamer in far enough that the shoulder is recessed in the gauge. All of this can be dome in a slowly turning drill press - you do not need a lathe although that is the best.

Peter Smith.

Barry Davies
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Joined: Tue Aug 24, 2010 12:11 pm

Re: .308 Headspace

#10 Postby Barry Davies » Thu Sep 21, 2017 3:42 pm

Check " Davies Triggers " web site ---" Gauges "
Barrry

BATattack
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Joined: Mon Dec 29, 2008 10:29 pm

Re: .308 Headspace

#11 Postby BATattack » Fri Sep 22, 2017 1:46 pm

if you want a basic idea get a piece or pieces of sticky tape and stick to the back of the case. use a razor blade to cut the tape to the exact size of the case head. keep layering until it becomes firm and then be a sure base to shoulder.

Best way is to do moderate load with a hard jam so the case is hard against the bolt face before firing. fire and measure using a gage like Pete has suggested.

Bigtravoz
Posts: 293
Joined: Sat Apr 22, 2017 7:43 pm

Re: .308 Headspace

#12 Postby Bigtravoz » Tue Sep 26, 2017 8:27 pm

Wouldn't a set of go no go gauges tell you what you need to know at the rifle end? As far as cases go fireformed twice to the chamber should have them perfectly matched to the chamber. New cases will always be formed to minimum case specs and those such as Winchester will be less than that (more than 6thou under minimum spec in the head with the current nraa hbc stuff and far from concentric.)

johnk
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Location: Brisbane

Re: .308 Headspace

#13 Postby johnk » Tue Sep 26, 2017 8:37 pm

Bigtravoz wrote:Wouldn't a set of go no go gauges tell you what you need to know at the rifle end?

No, I wanted to be comfortable that virgin brass could be fired in my precision chamber without the need to jam. It's a pain in the arse fireforming if the load isn't functionally useful (accurate) too & I have never found a jammed load that worked in my match rifle.

I was trying to find how others had found Stoney Point comparitors for that purpose.

As it turned out, it was all good. The new brass fits as snug as fired brass.


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