Re: case trim length in 223
RW,
I use a Lyman trimmer and sometimes I have to rechuck the case and trim a little more; the more the trimming, the more the tries to get it right. My guess is your 1.742 length is what the trimmer is set for and the first one first one just didn't get down far enough.
I personally would set your trimmer a little long, trim a few until I was confident in the length and then tighten down a little at a time and then lock it down.
I trim every time to eliminate the long trims. Necessary or not, that's what I do. I do not load plinkers and really don't know what defines a plinking round. If you're going to take the time to reload, load for precision.
CT