I don't have this gun with me anymore but it still kills me thinking about it and I really want to get this one back and get it sorted out at some point. This guy is awesome and has been one of my most appreciative and understanding clients and still comes to me for work. I recommended a set of parts for the guy and he threw it together himself or maybe had someone else do it since I was busy with other guns by the time he finally got all the parts together and he didn't want to bother me to rush it before his big game he had coming up. He used it for a day or two and brought it to me for an FPS bump the week before the game. He was getting 310 on .2g and wanted it as close to 350 as possible and based on the parts he got, I thought it was strange he wasn't getting at least 340. G&G ARP9 Full Lonex compression kit from Brill Armory Guarder 110 spring SHS full steel rack piston SHS 13:1 gears Prowin hop up unit (not my recommendation) Prometheus 128 mm inner barrel (recommended ZCI -- wasn't available) Rocket 22TPA motor (I recommended ZCI -- wasn't available) Maple leaf Omega Nub Maple leaf Super Macaron bucking 60 GATE TITAN Advanced A few parts were substituted for similar spec parts because he was in a rush to have it done. I wasn't consulted about the substitutes, but I think they're negligible to the end result and the ultimate problem that occurred. Upon opening the gearbox, I found that absolutely nothing was greased and his stock bushings were worn enough to let the axles wobble slightly. I also noticed the Lonex CH was the newer version with the padding on the front (not what was pictured in the listing on Brill), which I was a little skeptical about because of the reports about the padded Maxx heads shearing CH posts, but I hadn't heard anything about the Lonex ones being a problem so I left it in. I cleaned and lubricated everything and put in some fresh steel bushings. Swap the Rocket motor to a ZCI 22tpa I had in stock because the rocket sounded like **** and was drawing more amps than what I usually get with the ZCIs. Back together again and running smooth, lower amp draw, but it chronod high. I short stroked 2 teeth and it was bang on 350 fps on .2g BB. He goes to his big event and it gets through day 1 with no hiccups. Next day at the event it chronod like 250. ****. At least it wasn't misfeeding lmao. I get it back and go through it and find slight damage to the cylinder head posts as well as the mounting holes on the CH. FML. Airseal is still bang on, but I also find some odd damage to the hop rubber like the lips are hanging out of the chamber too far and the BBs are wearing a little ramp into the lip. I go pick up the stock barrel and chamber set from the guy and try every single combination of the 6 parts. No changes. I sand a spare confirmed good hop rubber ever so slightly one bit at a time and keep chroning after each bit of material removed and no changes until finally it chronos like 150 and it's not sealing. New rubber, and then sand a confirmed good nozzle by the same process and I get it up to 290FPS. I polish the piston and tappet tracks in the gearbox to ensure there are no hang ups anywhere and continue to inspect everything. No weird scoring on the nozzle. Everything seems to be aligned. I replaced the CH with an SHS one and it fit and sealed great and worked well with the nozzle. Tried replacing the piston o-ring and spring with confirmed good parts. No cracks in the body, BUT he's got a new 10" handguard on that's not fitting all the way against the receiver. Inner barrel was still the same and either the original outer barrel or the extension he put on wasn't allowing a longer barrel through. I take a look and the barrel nut is just too short to reach the receiver and the threads on the receiver have cracked off a chunk, still holds fine though and everything is centered. Just in case, I remove the rail and nut for further testing and brace the barrel assembly by hand, being sure the chamber is seated flat on the front of the gearbox and the nozzle is sealing to the rubber. No change. I figure the damage to the CH posts could be throwing off alignment ever so slightly to cause a problem so I rebuild and reshim the whole gearbox into an unused Lonex shell. I had to custom fit the Lonex shell to the ARP9 and it fit great in the end. Get it all together and I think I gained like 4-10 FPS on average. At this point I'm at my wits end and I try a Lonex tappet, Guarded tappet, SHS tappet and try it with and without tappet delayer to no avail. I had the intention of not charging the guy at all for the work since I figured I did something to **** it up. I ask that he give me $50 for the lonex shell and call it quits as I'd already been in a depressed state before this whole fiasco and the whole time I'm doing work on his gun, I'm only losing money in parts I can no longer sell as brand new, can't take on anymore jobs because I already have 2 customer jobs on deck, losing all confidence in myself as a tech, and I have 2 of my own replicas that I wanted to do some tests with, one being my first DSG build I had yet to tidy up and take to the field. What are the chances the body of his gun is just barely fucked up enough to not allow anything to work? Could the SHS cylinder head or something else be slightly messed up from the damaged posts in the original shell? I only put like 20 rounds through it with that CH and it looked totally fine. Could there be damage that's just not visible to the naked eye and could that really account for 50+ FPS loss? I'm so lost on this one but I really want to get this figured out. I'm generally quite good with machines and diagnosing issues and this is the first of about 30 guns I've worked on that has had such an elusive problem. The only things I didn't do were test it in another body or up the spring power but I didn't have any extra bodies laying around and I'm not keen on solving an obvious FPS issue with a stronger spring. The cylinder I used was over-volumed for the 128mm barrel with the intention he could use .2 or .25g BBs at 1.1j and joule creep closer to 1.49j with .3 or .32g BBs when he takes it outdoors. I tried chronoing with .3g and it hardly gained any energy. Did I miss something or this gun just cursed? Literally any suggestions are welcome. Thanks for reading if you made it this far. You're the real soldier.