ares striker ast01

Edgi nemo kit would solve your problems, including the undervolumed matter. I don't really know any other good upgrade kit for striker series out there. Maybe try escw piston and spring guide, which is a standard size so you wouldn't have to replace the cylinder at the cost of still low air volume : Set Piston & Spring Guide For Ares Striker As-01 E.s.c.w. Fps

For the sear, isn't AST comes with 90° already? I couldn't find any sear upgrade other than from Airsoftpro. You might try it, but I couldn't find any review of it yet as for now.

Do an intro post mate, just FYI

The problem with the Nemo kit is that it's nearly £400.....but, it does cover all your needs and is of course of superb quality. There are a couple of CO2 kits out there (depending on how much you love/hate CO2) and I believe Bespoke Airsoft has a fairly good selection in stock. Jaeger Precision makes upgrade parts for the Striker and do triggers IIRC but then you are left with the under volumed cylinder, leading to bigger springs, leading to more wear....

Didn't Ares make a copy version of the NEMO kit at almost 1/4 the price or something?

They do, but I heard mainly bad review about it. Cylinder tail not welded properly, cracks in the weld, etc. It's also sold everywhere where I could find it. Wonder is Ares working on something to improve it or something else. Been a while since they made something for a bolt action springer.