Ysterhout Dot Net
I took the results back to the machinist, who suggested opening the flash hole in the bushing slightly. I also suggested cutting the pocket a few thou deeper so I could seat the primers below flush.
Gen 2 of the bushings included the Winchester Large Rifle Magnum primers, and a test of the White River Large Rifle Magnum primers.
To avoid hang fires and misfires, I decided to put a fast burning pistol powder at the bottom of the case, then top it up with the BMG powder. I used a start load of BMG powder, and 4.5% by weight of that is the priming charge.
Conceptually, putting a fine ball powder underneath a coarse extruded powder would facilitate the finer power to migrate through the stack of coarse extruded powder, and that may affect ignition, so I figured some paper between the two layers would do.
I searched for chemicals to impregnate paper and make it burn quicker, and came across a ready made version called magician's paper. I bought several sheets, and a 20mm diameter hole punch.
I punched a circle of paper, inserted it into the case above the pistol powder, and topped up with Somchem B12.7 . Two grains of dacron held the powder column in place under the seated bullet, so nothing in the case could move around.
I also did some checking on the relative mass of primer compound present in various Large Rifle Magnum primers compared to the CCI 35. A large Rifle magnum primer provides the same energy to the load as several grains of rifle powder. A CCI 35 contains roughly 3x the quantity of primer compound than a large rifle magnum primer. 3 x 3 is nine, as a rough basis for the quantity of pistol powder that would be needed to compensate for the lower weight of priming compound in large rifle primers compared to CCI 35's.
I tested four rounds with CCI 35 primers with a charge of B12.7, and four rounds with each of Winchester and White River large rifle mangum primer using a duplex load of S121 plus the same charge of B12.7 as in the CCI35 primed cases. The duplex load is a small quantity of pistol powder in the bottom of the case, seperated from the main powder by a disc of nitrate paper. 2 grains of dacron are needed before seating the bullet to keep the powder column in place so the powder cannot move around.
