I just stumbled on to this thread and there is a lot to answer here.
1) Its not a head space issue
2) The reamers we use were based off of 140 Bergers. Now that being said we have been doing them for a while and not being SAMI specked lots of people have different reamers. The HSM ammo is a couple thou too long for my reamer it puts them right up in to the lands. The Nosler ammo is usually spot on
3) I have had this issue with a couple boxes of the 130s over the last year. I called Nosler on them with the lot number and both boxes were running reloader 19, dumped my loads and they were right at max. Took them down 1 grain and they were money.
4) Did it by chance happen after you cleaned the barrel? I have seen that occasionally as well on the 6.5x284s shooting the nosler ammo. It is right on the edge of hot and the increased resistance caused pressure.
5) If you are going to load give me a holler I can give you the load for the 140 bergers. If you are loading the 130s from nos. (what I would do) or get the preloaded 129 LR
I run the same case to ogive measurement on the 130s but run a more stable powder or less grains of the 19.
6) Hows the gun shooting??