- drilling and tapping for 8-32 stainless bolts and replacing all the crappy quality factory screws
- swapping the forend for an aluminum tube, the charger handle tube with an aluminum tube bonded to it with JB Weld steel filled epoxy
- dismantling and polishing all the magazine sliding surfaces such that failures to feed are eliminated
- polishing the chamber
- making a stronger charging handle out of drill rod
- making takedown for cleaning the bolt tool-free while adding a UHMW block to retain the bolt stop block
- swapping out the Chicago screws for HK push pins
- cleaning up friction interfaces in the FCG
- swapping out the recoil springs for a lighter pair which allow reliable cycling of subsonic ammunition and ONLY shooting CCI SV...
...this stuff and probably a few things I'm forgetting have made my GSG-16 fun to maintain, fun to shoot, and far less likely to fail. If I want to shoot hyper-velocity ammunition I'll use my 10/22 or Little Badger, but frankly if I want more power (and inevitably a bit less accuracy, as subsonic .22lr is superior for printing small groups at distance) I'll go to my 9mm PCC or 6.5CM Sig Cross. With .22lr I just don't see the point of going supersonic, with the inevitably increased potential for damage to rather delicately made guns like the 10/22 and GSG-16.
Not everybody has the skills, or the patience, or the motivation, to bother with stuff like this. I get it, most shooters want their full expectations met out of the box without tinkering in the workshop or paying a gunsmith to do such things. Fine, if that's you, an adjustment in expections-for-money are in order. You're not getting an out of the box $1,500 gun for $500. Period. The closest I've seen to such a shockingly good bargain is the Sig Cross. It's amazingly well made for what I regard to be a bargain price. And even then it's close to $2,500 after taxes. My Pardini K12 air pistol shoots incredibly well, essentially a perfect air pistol - and I paid $2,250 for it, so I expect it to perform more or less perfectly for that price. Even so I've had to replace all the seals after 8 years, because even a perfect airgun can't stay sealed forever. But that's not a fly in the ointment, it's maintenance. I wouldn't expect the same pinpoint accuracy from a Crosman 2240 at 1/20th the price, but I have rebuilt my 2240 into a precision PCP carbine with remarkable accuracy... at considerable cost in money and time, sort of like the GSG-16. Different approaches. Not a lot of overlap. Paying $1,500 for an out of the box rugged GSG-16 doesn't interest me, as the format makes it more of a range toy than a precision rifle, a fun plinker more than a serious 'weapon.' The GSG-16 is like the 2240 of .22lr - lots of room for modification/improvement with a low entry price.