Two things:
a) you mentioned a m120 spring, did you work on the gearbox? because assuming a perfect air seal and no teeth removed from the sector, a M120 will give way above 1.13J of energy.
b) what's your field like? Woodland or indoor CQB?
If your answer to B is cqb, then you won't need to change anything, as long as the bb goes somewhat straight for 20 or so metres you're golden. Maybe swap the rubber out for a Prometheus Purple if you really want to change something.
If the answer is woodland, then you might want to consider a couple of things:
- 0.2s are not up to the task, yes they fly out of your barrel pretty fast, but due to their low weight (and inertia) they lose power and speed pretty quickly, limiting your range;
- For average woodland usage, most people go for 0.28, 0.30 and 0.32g bbs, they have a lower initial velocity but due to their increased mass (and inertia) they hold onto their energy for longer, are less affected by wind and generally speaking they sport higher range. Some people use heavier (0.40 and upwards) because they
sleep under a bridge can afford it, somehow.
To get the best from these heavier weights, you need a hop up system that can support them.
This means a hop unit that is as rigid as it gets, especially around the hop arm, to give the most consistent pressure possible and a hop rubber with a concave contact patch. Barrels are not as important as people may think, as long as they are straight and aren't overly tight/wide they're okay.
Speaking of your case, Specna Cores come with an okay hop up chamber, which isn't the best in terms of rigidity (mine definitely weren't) but they are workable.
Maple Leaf hop rubbers (specifically Macarons and Super Macarons) are a good upgrade that doesn't cost money or mental health (looking at you R-Hops), they require a dedicated concave tensioner (Maple Leaf Omega or similar). Alternatively a PDI W-Hold with its B type tensioner, a generic flat hop even though it's outdated and finnicky to make.
Barrels: the ZCI mentioned are really good for what they cost, just be aware that being tighter than the stock Specna barrels they'll increase the energy.
I have two Specna Core guns, both run on Maxx units, Maple Leaf rubbers (60° Super Macaron on the C-02, 70° Super Macaron on the C-08), ZCI barrels (260mm C-02 and 247mm C-08), both guns can deliver 0.3g bbs at 60 metres while being sub 1J in energy (both around 0.97/0.98J).
Now the Maxx chambers are expensive and require some fiddling with, but imo you can't beat them in terms of consistency (no, plastic ZCI units aren't just as good, stop lying to yourself). You may need a different nozzle because they only want certain lengths.
A few considerations on rubber hardness:
Most people recommend 50s or 60s, I found 50s to be way, way too soft, especially the feed lips which tend to deform and fold in full auto causing power drops and inconsistent hop.
Don't bother with R-Hops, they still wear out and it's a pain to replace patches.
As said, flat hops are a thing of the past, it was done to mimic the R-Hop but without the hassle of preparing and gluing a rubber patch on the barrel. Most hop units don't even have enough range of adjustment to make up for the lack of material (there is no contact patch) and when I did them years ago, I had to get creative and make my own tensioners.
Overall upgrading your hop up system is one of the things I consider mandatory in order to get the best performance out of your RIF, but only if you can really exploit its potential.
