Case web expansion

[acooper1983]

I've got a question about case web expansion in my 708ai I cut a new piece of Papua 308 brass from which I'm sizing and fire forming so I know that the web is roughly .206 from that case head I'm running rather hot loads which is [email protected] gr primers are just slightly flattening case head exp measure .0005 .001 at the extreme. The web is measuring .467 avg for new brass and .473 for fired I realize I'm on the edge probably but is this safe ? Velocity avg from 26" barrel was 2800 @ 15 degrees Fahrenheit also did not have any sticky bolt issues or anything of that nature

 

[acooper1983]

case head on new brass avg is .4695 and goes to .470-.4705 after fireing. it seems from what im finding this is inspec and most brass doesnt measure exactly what its supposed to. is this correct?

 

[acooper1983]

a random 10% pull of my fire formed lapua brass

 

[Bill Johnson]

It seems, to me at least, that you are measuring the pressure ring rather then the web. I call it case head measuring and do it just forward of the extractor groove. Expansion runs in the .0001s range and is difficult to interpret for pressure indications but as a rule of thumb, I use .0003 as a maximum.

 

[MagnumManiac]

Sorry to burst your bubble, but measuring case head expansion is meaningless in the real world, it's about as accurate as measuring primer appearance as an indicator of pressure.
Also, it sounds like you're not measuring correctly, the expansion line is even less accurate because no case has even wall thickness all the way round it's circumference and thinner brass expands easier than thicker brass and may give false measurements depending on where you measure the case. It's a futile exercise trying to determine pressure measuring case head expansion.
Sticky extraction, ejector marks and scuffing of the case head if none of the others are present, is a sure sign of excessive pressure.
I have discovered excessive pressure closely follows these signs as it is increased, ejector marks are first, then hard bolt lift, then hard bolt lift AND sticky extraction, then all the above plus blown primers, then swollen case head and rupture, mallet required to open bolt and rifle damage in most cases. The range of pressure this occurrs in can be as little as a spread of 20, 000psi over maximum SAAMI pressure.
Plenty of folk load to 70, 000psl without knowing it because modern brass is stronger due to better alloying and smelter techniques, but once you get past this point, things go downhill quickly.

Cheers.
gun)

 

[Bill Johnson]

Sorry to burst your bubble, but measuring case head expansion is meaningless in the real world, it's about as accurate as measuring primer appearance as an indicator of pressure.
Also, it sounds like you're not measuring correctly, the expansion line is even less accurate because no case has even wall thickness all the way round it's circumference and thinner brass expands easier than thicker brass and may give false measurements depending on where you measure the case. It's a futile exercise trying to determine pressure measuring case head expansion.
Sticky extraction, ejector marks and scuffing of the case head if none of the others are present, is a sure sign of excessive pressure.
I have discovered excessive pressure closely follows these signs as it is increased, ejector marks are first, then hard bolt lift, then hard bolt lift AND sticky extraction, then all the above plus blown primers, then swollen case head and rupture, mallet required to open bolt and rifle damage in most cases. The range of pressure this occurrs in can be as little as a spread of 20, 000psi over maximum SAAMI pressure.
Plenty of folk load to 70, 000psl without knowing it because modern brass is stronger due to better alloying and smelter techniques, but once you get past this point, things go downhill quickly.

Cheers.
gun)

While the majority of your post is absolutely true, your first statement is off base. You may not be able to utilize case head expansion but there is definitely a corelation between pressure and head expansion.
Try this for a good read on the subject to start:

FEA Analysis of a Remington Model 7 action in 243 Winchester Caliber