I recommend just reading all the threads you can find. It will maybe take a few weeks to understand a full grasp of a lot, but it's worth it. It's somewhat of a short-term commitment.
Through my experience and reading on the inter-webs, here's a brief summary of what I learned to upgrade.
- Hop up bucking
- Barrel (with barrel spacers)
- (Optional) Hop up chamber (Action Army chamber is awesome)
- Hop up arm (Dangerwerx) or nub (Firefly Namazu)
- Teflon tape mods for compression.
- Upgraded Cylinder head (if you're having leaking or high fps variations)
- Upgraded 45 degree trigger sears or 90 degree trigger (main difference is that 90 has a really smooth bolt cycle. Works well with 500+ fps)
- Spring guide stopper
- Spring guide
- Upgraded Cylinder head
- Cylinder (Always last for springers because it's mainly cosmetic)
Since you have an AGM, not all the VSR upgrade parts will fit perfectly; therfore, you might have to modify some parts of your rifle.
If you're on a budget, I recommend just upgrading the accuracy portion and maybe throw in a m130 spring. This will provide good range, accuracy, and fps (410-450).
Also, read all of 1tonne's threads located in his sig. Super helpful.
I could be wrong on some things because I typed this up before sleeping and I have not research a ton on AGM VSR. Just throwing out what I learned through VSR and BAR threads and experience.
Edit: One thing to note: In AEG, the piston is being cycled and the cylinder is stationary (I think you would know that). In Springers, the piston and cylinder is moved together. Once the piston catches, the cylinder moves forward and locks.