Re: making .260 lapua brass?? advise please
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Stiller</div><div class="ubbcode-body">
My point in this is that given a case head with the same dimensions for the web thickness, head thickness and alloy type and temper, the pressures that a small rifle primer allows should be similar to the large. </div></div>
I disagree.
While web thickness in the <span style="color: #FF0000"><span style="font-weight: bold">axial</span></span> direction is of primary importance in predicting the max pressure for pistol cartridges with feed ramp intrusion into the supported chamber, it is only of secondary importance in cartridges supported back to the web. Strong rifles support to the web, except possibly for CZ527 with 22 Hornet bolt face is chambered and over chamfered for the 19 Badger [30 carbine case head].
What is of primary importance in predicting the maximum pressure in Mauser case heads is the web thickness in the <span style="color: #FF0000"><span style="font-weight: bold">radial</span></span> direction at the weakest spot, where the extractor groove impinges from the outside and the primer pocket intrudes from the inside.
The reason that the Mauser case head with large primer is never SAAMI registered above 65kpsi is because of loose primer pockets e.g. 6mmRem and 270Win.
This cross sectional area is, from specifications, between 0.084 and 0.095 sq inches in the RP 260 brass and between 0.095 and 0.108 square inches in the Lapua small primer 308 brass.
There is not a random distribution of product thought the specified range, but rather a more predicable nominal of 0.095 sq in for the RP and 0.106 sq for the Lapua.
This 14% difference would suggest that if [the large primer pocket brass is registered at 65 kpsi, can get long brass life with handloads for individual rifles at 70 kpsi, and has one shot short brass life at 75kpsi], then [the small primer brass could be registered at 74 kpsi, have long brass life at 80kpsi, and get one shot short brass life at 85 kpsi]. But it is not perfectly linear, and 6mmBR brass will not get loose primer pockets before the primer pierces. I have a couple of these rifles and they pierce CCI450 magnum small rifle primers. Gre-tan offers a service to bush the firing pin hole to allow an increase in the pressure before piercing. There is no SAAMI registered pressure for 6mmBR.
Max pressure for brass case heads can be better calculated with von Mises calculations, which I do not do, but Scott Sweet does. I only have his calculation for the large primer:
"The Mauser case head nominal condition chamber pressure for the initiation of case head yielding with H06 C26000 brass is: 76,977 psi".