Headspace conundrum

[MagnumManiac]

Are you checking with virgin brass?
7RM and .300WM are WAY short on headspace with virgin brass. Like .014-.018" short.

What absolute rubbish!
Yeah, the shoulder is short because it plays NO ROLE IN HEADSPACE.The case doesn't stretch in the web either…because it can't, only the shoulder blows forward and fills the void.

Cheers.

 

[59FLH]

Agreed. Only reason I asked was a quarter turn of a typical threaded Savage barrel (20tpi) would represent about 0.025 inch. That seems excessive. Am I incorrect in thinking the gage headspaces off the belt?

Actually 90 deg is .0125"................. just say'in.

Head space on Belted Mags is .22"(min) +.007"

Edit: Spelling and one to many zeros.

 

[lancetkenyon]

Agreed. Only reason I asked was a quarter turn of a typical threaded Savage barrel (20tpi) would represent about 0.025 inch. That seems excessive. Am I incorrect in thinking the gage headspaces off the belt?

Should

 

[lancetkenyon]

What absolute rubbish!
Yeah, the shoulder is short because it plays NO ROLE IN HEADSPACE.The case doesn't stretch in the web either…because it can't, only the shoulder blows forward and fills the void.

Cheers.

I disagree to some of this.
Yes, a belted magnum is supposed to headspace off the belt. But it still has play. Some brass much more than others. There are still big variations from base to top of belt in some brass.

But the case can and will most definitely stretch above the web. Both initially and upon subsequent firings if you are bumping the shoulders too far back. I bump shoulders like any other cartridge after they fully grow. .002-.003".

Have you never had a piece of belted magnum brass eventually have case head separation? I did on firing #10 on 1 piece of 7RM.

Why do you think Peterson .300WM Long brass is so popular?

 

[cajun]

I dont normally believe in coincidence but it could be just that. When I set up a savage I have it so the nogo is a hard nogo as in bolt wont break over but closes on the go. Did you try starting to thread the barrel in while indexing the lettering out 90 or 180 and see if it lines up?

 

[quigley257]

I love the Peterson long 300 WM brass. Even though we run match grade minimum size chamber reamers in our shop, most brass is WAY too short as it comes from the factory. The Peterson long brass prevents the initial .010 to .015 stretch that happens on the first firing of most factory brass. As far as headspace on a belted magnum, yes, they headspace solely off the belt. You need to have faith(or don't) that your reamer manufacturer made everything forward of the belt to a minimum spec or you can end up with a ton of case stretch on the first firing.

 

[Tiny Tim]

Actually 90 deg is .0125"................. just say'in.

Head space on Belted Mags is .22"(min) +.007"

Edit: Spelling and one to many zeros.

Yup. Your right. My miscalculation.

 

[MagnumManiac]

Why do you think Peterson .300WM Long brass is so popular?

The reason is because of statements made by people like you.
I have NEVER had a case head separation in belted brass because I understand the fundamentals and use chambers (A191) that control shoulder position…but I also use SAAMI match grade chambers and I NEVER bump more than .002" which when measured, due to spring back, is always around .0015".
I also have measured many belted cases from base to top of belt, I have a gauge for this, not once have I seen brass have a discrepancy as large as what you claim, biggest I've seen was Federal, it was .003" and I don't use that junk anyway.
Your statement stating that the brass stretches at the web on the first firing is the biggest bunch of crap I have ever herd.
Please EXPLAIN and show me PROOF that belted cases stretch at the web on the first firing…I so look forward to your foot being deeper in your mouth.
If a case STRETCHED the amount you imply on the first firing, it would fail on the second firing without a single question…it doesn't happen.
The number one cause of ANY head separation is excessive headspace, regardless of case type. The number one cause of this is reloaded induced excessive headspace…has NOTHING to do with case design.
Only case I have ever had head separations with is 6.5x55 Swede, the cases as new had .010" excessive headspace because the PMC company had sized them that way.

Cheers.

 

[Longtine88]

This was from some I measured a couple of years ago pondering it incase you wonder how much difference there is in the Long brass vs short.

So just measured some cases above the belt as follows:

ADG Saami Unfired: 0.5050"
ADGSaami Fired: 0.5090"

Peterson Long Unfired: 0.5080"
Peterson Long Fired: 0.5090"

To Mid Shoulder measurement:
ADG Saami unfired: 2.2615"
ADG Saami Fired: 2.2785"
Peterson Long unfired: 2.2750"
Peterson Long Fired: 2.2785"

 

[cdherman]

There's lots of variation between base to shoulder measurements out there. I once headspaced a Savage with a new 7mm SAUM barrel off of unfired brass using the "tried and true" scotch tape method. I had measured about 10 virgin cases base to shoulder and used the LONG one.

Well, after firing my break in rounds, I found I could not bump the shoulders back at all with my Redding dies. Why? Well the unfired factory brass was so short that I basically created a short headspace gun. I turned the barrel out a bit. Proper headspace gauges would have been better.

This is an anecdote, not attempt at a new controversy. It is fact. Factory unfired brass is often REALLY short.

Usually base to shoulder gets "fixed" in a given gun on first or second firing (not all loads finish the process on first firing, especially if starting some new load work up with new brass etc) As long as you don't resize the shoulder too far back, web separation, and excessive neck growth should not occur.

Belted magnums headspace off the belt only ONCE, if you want it that way. If you are careful and do not over re-size, keeping the shoulder only 1-2 thou under then the cartridge will headspace off of the shoulder like a regular non-belted bottle nose cartridge. There are guns with VERY generous belt cuts. They will destroy brass, if you FL resize. Think about it. If the firing pin drives a "loose: belted case forward, and then it stretches back on firing, you will get eventual separation. But in a gun with a loose belt, if you switch to headspacing off the shoulder, the location of the belt becomes moot.

Several other posters understand this as well. I just wanted to re-iterate it in different words, I guess.

 

[Longtine88]

There's lots of variation between base to shoulder measurements out there. I once headspaced a Savage with a new 7mm SAUM barrel off of unfired brass using the "tried and true" scotch tape method. I had measured about 10 virgin cases base to shoulder and used the LONG one.

Well, after firing my break in rounds, I found I could not bump the shoulders back at all with my Redding dies. Why? Well the unfired factory brass was so short that I basically created a short headspace gun. I turned the barrel out a bit. Proper headspace gauges would have been better.

This is an anecdote, not attempt at a new controversy. It is fact. Factory unfired brass is often REALLY short.

Usually base to shoulder gets "fixed" in a given gun on first or second firing (not all loads finish the process on first firing, especially if starting some new load work up with new brass etc) As long as you don't resize the shoulder too far back, web separation, and excessive neck growth should not occur.

Belted magnums headspace off the belt only ONCE, if you want it that way. If you are careful and do not over re-size, keeping the shoulder only 1-2 thou under then the cartridge will headspace off of the shoulder like a regular non-belted bottle nose cartridge. There are guns with VERY generous belt cuts. They will destroy brass, if you FL resize. Think about it. If the firing pin drives a "loose: belted case forward, and then it stretches back on firing, you will get eventual separation. But in a gun with a loose belt, if you switch to headspacing off the shoulder, the location of the belt becomes moot.

Several other posters understand this as well. I just wanted to re-iterate it in different words, I guess.

Yep I just wanted to show them on paper

 

[Cheezie]

Yep I just wanted to show them on paper

Very interesting! Makes total sense. So, using brass fired at least once in a particular rifle, and head spacing off the shoulder, is the best way to build accurate hunting loads in my 300 Winmags? And, for new brass, it should be fireformed before building hunting loads? And…(for barrel nut users) headspace to the belt should always be set very tight to prevent any base stretch?

 

[Carey Farmer]

Every piece of .264 Win Mag and 7mm Rem Mag brass I ever bought (from Nosler, Norma, ADG, or Peterson) was 0.013" to 0.017" short (at the shoulder datum) of the minimum SAAMI chamber dimension

Not exactly sure why, but that's how SAAMI set up chamber & cartridge dimensions for those (belted) cartridges: the case is supposed to be .011" to .028" shorter than the chamber at the shoulder datum. Never could figure out why, and it always bothered me, so I had my .264 Win Mag reamer made up with the belt-to-shoulder dimension 0.010" shorter than SAAMI. Problem solved.

 

[kfreeze]

This is just what you will have with savage. If the lettering always lined up, you would be able to buy shouldered prefit barrels for the actions. You are only seeing the difference in tolerance of the parts made. I would bet that if you had 100 actions made at all differnet times over 30+ years that you would see more different places of the stampings. And I would guess that newer actions are more consistant than older actions for where the stampings line up.