450Bushmaster.net

Just tried trimming my new brass to length. Wondering if it has to be sized and expanded first, as my trimmer pilot won't begin to enter the case mouth.
I was also surprised to see that the case is actually tapered . Hoot mentioned in an article that the Hornady expander opens the case a little to much for good retention. What is the solution to that one? Thought aaaai should get answers before screwing up fifty rounds of new brass.

You should measure them before you trim them. Not a single one I got was the spec 1.70 length. They will shrink a little after each subsequent loading, so why make them any shorter before you even start? When I load a group of 5, I do try to use ones the same length. I sort them in Plano compartmental boxes by (number of times reloaded - resized length) in .002 jumps. IE 2X1.685/86, 3X1.687/88, 4X1.689/90, 5X1.691-92 etc. I had bought a Lee trim cutter set and had to chuck it in the drill press and turn it down a little with some 400 wet-or-dry until it fit in the mouths. I'm a proponent of not using the expander in the interest of maximum neck tension. I just guide the bullet in until it barely starts, then rotate them in 1/3 turns with two deepening additional seating plunges until it reach the stop point. Might be overkill, but for what it costs to reload this beast, I figure why not go the extra distance ensuring accuracy. I'm not into Blammo Ammo shooting.

Hoot

Hoot is correct. Do not trim your new brass. While they may not be all the "exact" same length, they are shorter than the 1.70" maximum length. I have a box of new brass and they are shorter.

The case mouths ID on the new brass measure .447". Fill 'em with powder, seat the bullets, and your good to go. No need to size and expand new brass -- needless step.

Also, I do the same as Hoot -- size only and do not expand. The sized cases measure .446" ID and using the expander, they measure .448" ID. The extra .002" is helpful for neck tension.