I do use a F-1 Master Chrony. Could it be off a little, yes, but that is what it said, at least what I wrote down

There are a lot of people on the net who claim to push well over 4k fps, not sure I'd want to push mine much more than what I do. Wolf primers are known to be hard primers and I do get signs of just beginning flat primer, but no cupping or blow outs.
Nosler gives a max load of 23.5 grs of RL7 with their 40 gr varminter at just over 3.6k fps. Is it really that un-realistic to push that load another 400 fps? I don't think so.
Hornady lists there factor 223 Rem 35 gr NTX® Superformance at 4k fps at the muzzle and the 53 gr. at 3.5k fps. Does it really do that? Don't know but possible.
Maybe in your 40 years of experience you have not pushed the extremes with your rifle, I have a habit to do so. Dangerous? yes, very. I would not recommend it to most, it is something you have to decide for yourself.
Again back to the OP, I like to have both a 223 and 243 and even the 25-06. The .223 is nice to have when you can not have anything bigger in the field. just my
