Understanding SAAMI cartridge specs in regard to FL Sizing

[freid]

Just looking for a bit of guidance and to check my understanding.

The below is the SAAMI spec for the .270W cartridge.



Am I correct in reading the that min and max headspaces are:
Min = 2.046 (2.053-0.007)
Max =2.053

And as such, should I expect my FL Sizing Die, when bottoming out on the shell holder, would in theory resize to 2.046 (appreciate different dies and shell holders could mean there are small variables, but that is the theory correct?).

I'll measure some cases, but just wanted to check the theory too.

 

[freid]

Anyone?!

 

[Stumpy2]

In theory, yes. But there are a lot of variables involved, which is why there are minimum and maximum measurements.

 

[Ronin]

No

Headspace - Saami and CIp spec are taken from a point (datum) somewhere along the line of the shoulder

Unless your measurement tool uses the exact same point of reference along that line of the shoulder - you will get an “incorrect” reading leading to confusion thinking something is wrong

You are better - if you are setting up uour die set

To remove firing pin assembly from bolt then incrementally size a piece of fired brass down to a point the bolt will close under gentle finger pressure (not to a point it drops under its own weight)

Set die locking ring and forget

 

[freid]

No

Headspace - Saami and CIp spec are taken from a point (datum) somewhere along the line of the shoulder

Unless your measurement tool uses the exact same point of reference along that line of the shoulder - you will get an “incorrect” reading leading to confusion thinking something is wrong

You are better - if you are setting up uour die set

To remove firing pin assembly from bolt then incrementally size a piece of fired brass down to a point the bolt will close under gentle finger pressure (not to a point it drops under its own weight)

Set die locking ring and forget

Ronin,

Thank you that’s is helpful and makes sense. I had considered doing this, but read that you also needed to remove the extractor. I can remove the firing pin easily enough (Sako 75 and A1) but I don’t have suitable tool to remove the extractor.

Can I just use your method with the extractor still in but firing pin out?!

 

[Ronin]

No need to remove extractor at all

 

[Edinburgh Rifles]

your chamber and die may bear no resemblance to the SAMMI spec…

Size brass to YOUR rifle as above
Your size 12 shoes may not be the same as my size 12 feet

Ignore the specifications at the design level and work with what you have to make aure your brass is the best size for your chamber.

I defy anyone to reliable measure angular surfaces and datum points with cheap tools with huge accuracy tolerances

 

[freid]

Ronin, Ed,

Makes perfect sense. Thank you both.

 

[jthyttin]

For completeness sake, you get most consistent results by removing everything that forces the case. I.e. extractor if it puts sideways pressure to case, and plunger / ejector if it's located in bolt head (I think your Sakos have fixed ejector i.e. slot cut to bolt head and corresponding blade inside action). Removal of firing pin assembly removes the cocking function i.e. enables you to feel the bolt movement with no distractions.

Personally I go for the bolt dropping on it's own, and even then add the tiniest bit for clearance. Or in some cases use cartridge gauge.

You should also have sturdy press that flexes consistently under load. Otherwise you need a set of graduated shell holders and instead of adjusting the die you change holders until the desired level of sizing is achieved.

 

[deeangeo]

Personally, I set my F/L sizing die to 'Fired case' headspace dimensions. I simply use the Hornady headspace comparator to determine the dimension & find the benefit of somewhat extended cartridge life by this method. Naturally doing this ensures I'm not resizing to SAAMI/CIP dimensions. Resizing to SAAMI/CIP ensures the cartridge may be fired in ANY rifle rather than being tuned to your own rifle. (Also annealing cases after each 3 firings) Just my personal take though, but I find it works for me.

 

[Dalua]

Ronin,

Thank you that’s is helpful and makes sense. I had considered doing this, but read that you also needed to remove the extractor. I can remove the firing pin easily enough (Sako 75 and A1) but I don’t have suitable tool to remove the extractor.

Can I just use your method with the extractor still in but firing pin out?!

I wonder whether you're thinking, rather than the extractor, of the spring-loaded ejector found in the bolt-face of some rifles?

That certainly would need to come out, but fortunately SAKO A1 and 75 don't have one.

 

[kenbro]

The ejector definitely needs out with my Remington.
Kb.

 

[Mr Tree]

When I first started FL resizing, I set the die to touch shell holder, it was a long way shorter than my rifle chamber, the advice given here by Ronin & Edinburgh Rifles is spot on. Wish I knew that then, I now have many cases still after firing that are still too short, & vary in length, my .222 does not stretch the case that much. Your .270 probably will.

 

[trickie]

I follow the @Ronin method, remove the firing pin and measure for slight pressure to close/open

 

[scotch_egg]

A great video on the subject