You ordered an airsoft gun from outside of Canada?
You didnt look into anything befor hand did you?
I wish u luck in getting it.
The BB's you have are okay but .28's or .30's would be best for such a high power set up. even in the 375-400 range 28 or .30 work well, much beter then .20 that will be much less stable becaus ethey are so light and flyin so fast. you may even want to try some .36 if your rifle can provide enough hop up, if you get it.
The lighter bb's will be ok for targetr shoting at a short range but longer range youll notice a big diff in the heavier rounds ability to remain stable and keep your groupings tighter
Also BBBastards are prolly the best BB's around theese parts, and they are a Canadian company!!
Get Age verrified folks will be a lil more helpfull, tho i dunno with this importing on your own thing check out the FAQ's here