My son just got a gen 1 avenger in .177 for a pretty big discount, so far he has shot 7.9gr premier crosman hollow points and those are shooting really well, he also shot the RWS R10 match 7.0gr pellets and those have not done as well as the premiers, but still aint bad. He bought some 8.5gr gold flights but weather hasnt been nice enough to try those yet, and supply of JSB and H&N 177's has been limited to us, so we are just trying different pellets here and there as we can get them, but for the price the premiers are 25yd tack drivers producing dime sized groups which for the price is completely acceptable in my mind. I am sure one of the JSB or H&N variants will be the most accurate, I wish we could get our hands on some for decent normal price right now, my guess is the JSB 8.4's you already have will be some of the better pellets for it, from what I have seen on the youtube videos we have watched they seem to prefer heavier pellets in the 8-9gr area.
