Re: 300 rum case trim length?
I trim mine to 2.830 each time, but my chamber appears to be shorter and 2.840 is too long for mine. I made a case to measure my chamber length and 2.835 is all I let mine get to.
If you have a dremmel with a cutoff wheel, or a hacksaw, cut a ring off the neck on a sized case about 3/16" long or so and split it and chamfer edges. Seat a bullet in this case, pinch and slip the ring over the bullet leaving it out long on the bullet so when you chamber it that it will hit the end of the chamber and be pushed back on the bullet so you can measure the chamber length. Measure from the base of the case to the front edge of the ring and use this number as your max chamber length. I keep my cases trimmed back from this point .010, and .005 from the chamber max is all the closer I ever allow them to get.
You just don't want to let the cases get too long and be forced up into the leade and pinch the neck around the bullet tight, as pressures can skyrocket.