My "match" rifle is an M5 Mausingfield, for which I have a 6BRA and 6.5 Creedmoor barrels. It's one of my favorite actions, if not my absolute favorite action. When timed with a trigger, the bolt lift and bolt close is exceptionally light. The action runs like a sewing machine, and has no issues at all in really adverse conditions with high wind and debris. Never had an issue with extraction, or any other action related reliability issues with the Mausingfield.
My .300NM is built on a Defiance, with polished rails and DLC surface treatment. Silky smooth, haven't had any reliability issues, but haven't really shot it for extended periods in adverse conditions. I haven't had any issues with it, but my rifle does run into pressure earlier then other .300NM's. In other threads, I've heard mention/reference to pressure being encountered early in large caliber systems in actions that have "smaller" lugs. The Defiance does have small(ish) lugs for a lapua bolt faced cartridge, or so I am told. I've talked to a few different people about whether that should cause early pressure issues or not, with no real consensus on that subject.
Lot's of good actions out there these days. Lone Peak makes a great action with their Fuzions, so that's also worth a look. A Surgeon 1581XL is a great candidate, but you are limited on stocks and chassis that have that footprint, and the tennon requires barrels with a larger tennon OD (1.35" I believe), which limits your barrel options and drives up price a bit.
