My BIL invited me to a team-match in February. He shoots competition precision rifle (.338 lapua) on the reg. This match is a 2 person team with one prescision shooter and one AR shooter. I will be the AR shooter.

Not new to the platform and this will be my first match.  I'm really looking forward to it. Estimated max range for the course of fire is 400 yds.

I have a couple guns I could take and am looking for input:

Colt with 16" pencil barrel and RDS or 1x4.

Ambush Arms (Daniel's Defense) 18" barrel with P223 3 x 9 and 45 degree offset BUIS.

10.3 SBR w/Rainier Arms match-grade .223 Wylde. RDS.

I know the obvious answer is whichever one I am most proficient with, which is hard to say. My plan is to pick one and practice with it between now and the match.

In addition to which gun to take any input on Ammo would be appreciated.

Thanks for the input.

At 400 yards against a shot timer, I'd want a magnified optic.  Personally, I'd do the 18" with the 3-9x and offset irons.