Had a huge POI shift on mine (~3 moa to the 6 o'clock). However once I had it on, there was no problem with accuracy (TRG-42). I put a witness mark on mine to ensure I ratcheted it to the same position every time.
So yes, 1:10 TRG-42 in .338. I am using a 250 Scenar over 90 gr. of 4831sc (max load according to the Sierra manual). Don't recall OAL off the top of my head, but it's 0.020 less than mag length. Gives me 3017 fps with a SD of 11.
Scary accurate. I've been meaning to try the Hornady 285's but life has been precluding me from developing a new load right now.