Case Head Thrust

[Lone Star]

There has been some contention (!) recently about how this value is calculated.  Some believe that it is the case head area times the chamber pressure, others maintain that it is the internal case area times that pressure.  Apparently few of the former posters have ever looked for definative sources on the matter.  I offer the following sources to support the latter case - that it is not the case head dimension which matters.

Dan Lilja, well-known barrel maker and gunsmith (with an engineering background) knows the correct method and uses it when he evaluates the strength of various rifle actions....read about it here:
http://www.riflebarrels.com/articles/custom_actions/bolt_lug_strength.htm

So does John Linebaugh (maker of mega-powerful revolvers), although because he deals with straight-walled cases he has to use the case mouth diameter in his calculations:
http://gunsandmoreguns.com/html/body_45coltmyth.html

Note that neither of the respected gentleman above mentions the case head size in their discussions.  This is because it doesn't matter.  If you don't want to believe me (an engineer who works with high pressure containment daily) then perhaps the credibility of the two gents above will convince you.  

[Duffy]

Bolt thrust is easy to calculate. Only two inputs are required. They are peak chamber pressure in PSI and as mentioned, the inside area of the case head that the gas pressure can work on. The formula then is:

THRUST=AREA*CPSI Where:

AREA=3.1416*(HS/2)^2

HS=the diameter of the inside of the case head.

[Questor]

Why is there a controversy? What application does this have to a handloader?  As a handloader, about the only thing I need to worry that relates to this is to not put lubricated cartridges in my chamber.