Re: Question about pressure
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tbshltn</div><div class="ubbcode-body">Also what is safe pressure. </div></div>
Steel has a certain property that below 1/2 of its maximum stress level, the barrel can absorb an essentially unlimited number of pressure cycles. Above this level, the steel is slowly (and literally) comming apart at the seams. Many barrel steels have this one shot maximal pressure level very near 100K PSI, whereas mild steel with perfect grain structure has 80K PSI max for a single firing. This is wy 'proof' loads are in the 75K-80K range. If the barrel is going to blow up at SAMMI pressures within the life of a normal barrel it will blow up on the proof firing.
Thus, in a pendanic sense, everything over 50K PSI is wearing out the barrel at the grain boundary level.
However, it is generally considered that anything under 58K PSI is safe in a barrel of modern vintage and action of modern metalurgy, this is the pressure at which brass changes from being a solid into being a putty-like substance and where brass begins to flow. Older guns such as WW-II Mausers are not supposed to be taken over 52K PSI. Winchester 92, 94s should not be taken over 42K PSI.
Now, if you happen to count the rounds through the gun, maintain the gun meticulously, and monitor the brass comming out of the gun, and change barrels when they start to wear out; pressures in modern gun metalurgies can be 'safely' taken up to 62K PSI knowing that you are slowly wearing out the barrel, bolt, and action. This is the pressure range of the 5.56*45 cartrige in AR15/M16s... Bolts are routinly changed out between 5K-10K rounds, with wear on various other critical and semi-critical parts {Barrels, cam key, BCG carrier rails, and importantly the barrel breech.}
Almost anything over 62K PSI is dangerous in terms of hundreds of rounds, years of use, temperature extremes. Once or twice, you can get away with it, however, a steady diet is going to get you in trouble; someday.
Be safe.
