I would highly recommend the push pin upgrade, hammer strut mod, and trigger mod. The hammer strut is a biggie. You don't want to crack your bolt this mod should prevent that and make cleaning a bit easier. But push pin first. You don't need to do hammer strut just yet. Go have some fun with it first. Warning you will see how dirty your gun gets just after a couple of rounds I promise. Hammer strut mod should help with that and much more go read hammer strut mod for more info. Also very picky on ammo I use cci stinger, cci blazer 525 bulk, remington viper, subsonic, yellow jacket, and aguliar super max. Others have gotten away with other ammo's but these are what work for me with very little or no fte or ftf. There are other internal mod that I did to my pk that you could find on this form and some I did myself to improve the gun if you like to know just let me know. But yeah the gsg5 isn't a gun that's perfect that needs improvement in areas but good gun I have no regrets.