headspace

blueprairiedog

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I have struggled with the .243 WSSM. I purchased three used Model 70s and had a gunsmith chamber a custom barrel to replace one of the factory barrels. I purchased full length sizing die from Forster. It would not size the cases enough to close in any of the chambers. I purchased a Redding Full length Bushing die and the same story. In despiration, I purchased a RCBS full length size die and it would not size cases to fit the chamber. In desperation, a friend tried a Redding full length size die in .300 Remington Ultra Mag. It was successful in sizing the base of the cartridge to fit the chamber. He used the Redding Ultra press. The .300 RUM die split under the pressure and I got a hundred cases to fit. Those cases would fit any of the chambers. My former friend would not risk the replacement die I purchased for any more cases. I had Whidden build a die to size cases and it works, but my RCBS Rock Chucker does not have enough leverage to close the die on the shell holder and I have to get someone else to size for me. My conclusion is that there is a disconnect between what the die makers and rifle makers believe are the specifications.
Commercially acceptable? I have not figured out what that truly means other than manufacturers think it’s okay
 

entoptics

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FWIW, In my experience, new brass is nearly useless as a headspace measuring tool relative to SAAMI. In my experience, it's almost always at the absolute bottom of SAAMI specs, if not below.

0.008" growth on first firing wouldn't even make me blink. I had 0.031" growth on my 264 WM with Remington brass. That's on a Savage prefit, set with a Go-gauge, and confirmed No-Go with a piece of scotch tape on the Go-gauge (i.e. ≤ 0.003 above SAAMI minimum). ADG 7mm Rem Mag brass, was >0.010" growth, on my other Savage with headspace set the same.

My buddy's 30-06 (Factory pre-64 M70) had the tightest factory headspace I've ever seen, and new vs once fired was still ~0.010" with Remington brass.

Factory new brass (either component or loaded ammo) is SHORT usually. Presumably they want it to reliably feed in the shortest chamber imaginable. They're only responsible for that first shot, so have no concern about us reloaders who want to get a few shots on a piece brass before it comes unglued at the web...(well, except for the Peterson "Long" offerings 👏 )
 

chav0_12

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I have struggled with the .243 WSSM. I purchased three used Model 70s and had a gunsmith chamber a custom barrel to replace one of the factory barrels. I purchased full length sizing die from Forster. It would not size the cases enough to close in any of the chambers. I purchased a Redding Full length Bushing die and the same story. In despiration, I purchased a RCBS full length size die and it would not size cases to fit the chamber. In desperation, a friend tried a Redding full length size die in .300 Remington Ultra Mag. It was successful in sizing the base of the cartridge to fit the chamber. He used the Redding Ultra press. The .300 RUM die split under the pressure and I got a hundred cases to fit. Those cases would fit any of the chambers. My former friend would not risk the replacement die I purchased for any more cases. I had Whidden build a die to size cases and it works, but my RCBS Rock Chucker does not have enough leverage to close the die on the shell holder and I have to get someone else to size for me. My conclusion is that there is a disconnect between what the die makers and rifle makers believe are the specifications.
Sounds like there’s some other problem there. I have a Redding FL die for my 243 WSSM Browning A-Bolt II and I’ve never had any issues like that.
 

chav0_12

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FWIW, In my experience, new brass is nearly useless as a headspace measuring tool relative to SAAMI. In my experience, it's almost always at the absolute bottom of SAAMI specs, if not below.

0.008" growth on first firing wouldn't even make me blink. I had 0.031" growth on my 264 WM with Remington brass. That's on a Savage prefit, set with a Go-gauge, and confirmed No-Go with a piece of scotch tape on the Go-gauge (i.e. ≤ 0.003 above SAAMI minimum). ADG 7mm Rem Mag brass, was >0.010" growth, on my other Savage with headspace set the same.

My buddy's 30-06 (Factory pre-64 M70) had the tightest factory headspace I've ever seen, and new vs once fired was still ~0.010" with Remington brass.

Factory new brass (either component or loaded ammo) is SHORT usually. Presumably they want it to reliably feed in the shortest chamber imaginable. They're only responsible for that first shot, so have no concern about us reloaders who want to get a few shots on a piece brass before it comes unglued at the web...(well, except for the Peterson "Long" offerings 👏 )
I think you’re also comparing belted cases to rimless cases which headspace differently. I’ve noticed in a couple different 300 Win Mags some early case failures which I could only assume to be due to over sizing. The most recent is on a buddy’s CA Mesa, he’s having a lot of case head separations thankfully none have been catastrophic. Initially when I taught him how to size I showed him how to do a complete FL size, now I can’t get him to just bump the shoulder which I would assume would save some case life.
 

blueprairiedog

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At the end of the day I like what ontarget7 said 0.002 if I have 0.003 that’s the max I can live with and I usually start looking for a barrel even on old military rifles. I am waiting on a 30-06 reamer from ptg for the new barrel I put on the 03A3 but the gun shot fine with the old barrel I just think it would be better in the long run as far as buying brass if it wasn’t so long in the chamber
 

entoptics

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Look at the SAAMI drawings and there'd be little discussion. Max cartridge and min chamber on the same page. Max cartridge is always smaller than min chamber, so a factory cartridge or new piece of brass will tell you nothing about headspace, even with tape stuck to it.
https://saami.org/wp-content/upload...99.4-CFR-Approved-2015-12-14-Posting-Copy.pdf
Click Here for a link to a PDF with all the current SAAMI drawings...

Here's 243 WSSM
Screen Shot 2021-10-17 at 5.15.21 PM.png

As @shortgrass and I (and others) mentioned, unfired brass isn't all that helpful in headspace calculations, other than to get an idea of how hard the first firing might be on the brass. All subsequent firings should be bumped 0.002" back anyway from your chamber dimension, so it's only the initial growth that maters for head separation potential if you're doing things right.

For 243 WSSM, a "shortest" scenario is minimum chamber headspace @ 1.2403" and maximum brass size of 1.2434", which would result in a 0.003" crush on the brass (i.e. might not even chamber).

The "longest" scenario is 1.2503" + 0.015 Tolerance for a total headspace of 1.2653" headspace and a minimum brass size of 1.2434" - 0.007" or 1.2364" brass. This will result in 0.0289" of brass growth on firing.

In my experience, brass makers NEVER make their stuff near max, and usually near minimum or less. So, with a properly setup rifle using Go and No-Go gauges, the headspace would be a little above minimum, say 0.004" (1.2443), to accommodate the worst case scenario maximum length brass (1.2434"). Take a piece of minimum SAAMI length brass (1.2364") and fire it in that perfectly head spaced chamber, and she'll grow 0.007".

Even if the OP's new brass started at Maximum SAAMI length (unlikely), then grew 0.008" on firing, the chamber would still be at or below the SAAMI max allowed.
 

ontarget7

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Yeah, using brass to set headspace is a very bad idea. I am a gunsmith and just the liability of that is scary. Also there is a difference between bolt nose clearance and headspace.
Could you explain ?

It’s quite easy to measure your fired brass and your loaded rounds to get proper headspace for your particular chamber.

From there you can identify if your bumping the shoulder to much, not enough or right where you desire for your specific load.
 

RuninL8

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Could you explain ?

It’s quite easy to measure your fired brass and your loaded rounds to get proper headspace for your particular chamber.

From there you can identify if your bumping the shoulder to much, not enough or right where you desire for your specific load.
I'm talking about using a piece of brass to chamber a new barrel or to set the the headspace on a pre-chambered barrel.
 

RuninL8

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I guess when I read headspace, I immediately thought someone was talking about setting a chamber. I read the thread with that in mind not realizing they were just talking about bumbing brass. I saw .006 on headspace and got a little worried. Lol I'll learn to read one day.
 

ontarget7

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I guess when I read headspace, I immediately thought someone was talking about setting a chamber. I read the thread with that in mind not realizing they were just talking about bumbing brass. I saw .006 on headspace and got a little worried. Lol I'll learn to read one day.
All good, brother !
I feel the two have been used throughout this thread and the reason I wanted to clarify.
Thank You !
 

shortgrass

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In my mind, headspace is gauging the length of the chamber from datum to bolt face. Thanks to the internet "headspace" now means 2 different things, one of which is not correct. Cartridge fit is not headspace. Only the distance from datum to bolt face is. Brass is not made to the same tolerances that hardened steel gauges are. Brass is malleable, it can be shaped easily. Upon firing the brass 'swells' to me the chamber walls and when pressure drops, it contracts. Any material that can move that much is not a "gauge".
 
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