04-17-2020, 09:30 AM
A. Sierra has pressure-measuring equipment; they are speaking to the entire range of bullet jumps, from one boundary - deep in the base, to the other boundary - touching lands. With some kind of convex curve in between.
B. Don't know if Vaughn has pressure-measuring equipment. He is speaking about 1/2 of the range - going from the lands back to about 0.060 jump. With a decrease going from lands back to 0.060.
Changing bullet jump also affects the timing of the arrival of the bullet at the muzzle, not just peak pressure; such a timing change can affect accuracy (OBT theory) even if exit MV is not affected.
Neither quote-source specifically mentions MV in their discussion, that I can see anyway.
Remember it's not the pmax per se, but the integral of pressure-over-distance, that gives you the exit MV.
There are probably a couple other variables at work in all of this, too, that we haven't thought of.
The only study I read that showed a difference was that seating the bullet further out sometimes allowed more powder to be added of a desired type (IIRC 0.1 or 0.2gr), which in turn would give him a bit more MV.
B. Don't know if Vaughn has pressure-measuring equipment. He is speaking about 1/2 of the range - going from the lands back to about 0.060 jump. With a decrease going from lands back to 0.060.
Changing bullet jump also affects the timing of the arrival of the bullet at the muzzle, not just peak pressure; such a timing change can affect accuracy (OBT theory) even if exit MV is not affected.
Neither quote-source specifically mentions MV in their discussion, that I can see anyway.
Remember it's not the pmax per se, but the integral of pressure-over-distance, that gives you the exit MV.
There are probably a couple other variables at work in all of this, too, that we haven't thought of.
The only study I read that showed a difference was that seating the bullet further out sometimes allowed more powder to be added of a desired type (IIRC 0.1 or 0.2gr), which in turn would give him a bit more MV.
"Down the floor, out the door, Go Brandon Go!!!!!"