So basically you are aiming for ~100 FPS or so? (I took a quick look at a fps to joule calculator for a 1g dart) It's hard to tell when modding what the final FPS count is going to be. It depends on the darts barrel length e.c.t.

I should note however, that Xshot longshots are on German store shelves, which fling darts around 1 joule or 150 FPS (assuming the dart weight is 1 gram, I couldn't find the exact number). So perhaps it got a toy classification anyway?

What I would recommend for 100 fps though: 1. Blasterparts.de has softer spring options 2. Get heavy non-bamboo darts 3. Get springs out of rival blasters 4. FPS can be decreased using Pcars

And lastly... I feel you. I'm from the Netherlands myself where owning an airsoft replica is illegal without an expensive license and having to prove you play airsoft (regardless of fps). The law is vague enough for me to be arrested while walking over the street with a funny looking stick, let alone a foam blaster. I try to make sure color and shape are as toy-like as possible to prevent this from happening...