That is weird... Too much pressure on brass cased ammo, but not enough on steel cased ammo. I read that the failure with the steel cased ammo you are experiencing is most likey because the steel cases don't expand in the chamber as brass does, thereby "sealing" the case in the chamber and not allowing excess gas to exit rearward, where the steel case doesn't expand, allowing the gas to escape towards the chamber, causing failure to cycle.
Then, with your brass ammo, it seems you are overpressured. For this, I would recommend looking into either a heavier buffer and/or a Wolff or Tubbs xtra power buffer spring to slow down the cycling and ease the extraction.
But, seeings how you are low on time, I would just recommend calling Remington. Read the owners manual first, because some companies will void your warranty if you shoot any type of ammo they don't recommend you fire, such as steel cased ammo or anything other than "match grade". Good luck!
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