The pierce is a tough time on any pistol in the cold. I found using marker oil instead of the tippmann grease. After an hour or 2 of play the other day i reoiled it by dripping 3 or 4 drops into the pierce pin block. It reminded me pleasantly of the game Chutes Away! but with oil...that was at 2bags.
I also put a coat of oil on both sides of the bumper.
I hope that helps!
We play Pistol and we encourage the Few despite the discouragement of the Many.