Re: 338 Lapua and lug sheer
Jerry,
First, this is an excellent thread as it deals with a something so often lacking: FACTS.
Bravo sir!
Now for questions from Chad's little mind.
1. A gent you may know named Justin also works for Ratheon out in Tuscon, AZ. He too is an engineer (ME) and over dinner one evening years ago at nationals he was describing a gun as nothing more than a pressure vessel. Pressure reacts to whatever surface it contacts with at a right angle.
So, this has lead to my squeaky wheels turning a bit. If this is indeed the case then how does one go about configuring exactly how much pressure is exerted on the bolt face and consequently transmitted to the lugs? I realize the thin walled case isn't going to resist the pressures in a cartridge all that much, but it is a viable component to determining this kind of stuff. (Isn't it? I wonder. . .)
I base this on a little experiment I did once upon a time. I shot my 1022 with my thumb holding the charging handle closed. With sufficient force I was able to prevent the bolt from moving to the rear. According to a chart I have (click link below) the lowly 22LR is rated to 24K psi. If this is indeed correct then was I able to overcome 24Kpsi with nothing more elaborate than my "manly" thumb? (my ego's at stake here, be gentle
)
Common sense suggests to me that no I'm not because I can still dislocate my right thumb by looking at it funny due to a H/S football mishap.
Does it then become a function of surface area? The 22LR rim measures a bit over a quarter inch in diameter. Equating to around .055" square inches. It would stand to reason that if we bumped that up to say a whole square inch then there's a bit more "traction" for the case head to push stuff around.
The 338LM rim measures .585" and has .266" of surface area. If memory serves me correct it runs around 64Kpsi (CUP) I don't know the conversions between CUP and PSI.
So we have a cartridge developing 2.6 times the pressure as the 22 LR with 4.8 times the case head surface area.
How many "thumbs" is that?
Your thoughts are encouraged and I appreciate your time.
All the best,
C
http://www.lasc.us/SAAMIMaxPressure.htm