have a look on the airgun BBS , venom kit will transform your hw77 alot,they reduce the lock time tremendously and come with a new piston seal/washers etc everything you need.Then you have a kit supplied by a member called BONNIE AND CLYDE they are half the price and good kits also, another good spring is a POK spring, yet again a member on the bbs known as POK.OX springs can be quite shite,had one snap in a rifle once now that was bad LOL if your going to upgrade spend the extra dosh and make your springer a goodun,