The 455 has a tight bore. I use a .20 cal dewey rod and jag with a delrin bore guide. .20 and .22 nylon brushes seem to be ok. I use a bore snake after each use and clean every 300-500 rounds or when accuracy falls off...whichever comes first.
My budget build:
Remington 700 AAC-SD in .308
XLR element chassis with the folding option
XLR 20 moa base
TPS low rings
Krg bolt lift
Timney 510 trigger
Harris 6-9 with pod loc
Vortex viper pst 6-24 x 50