UKARA is proof that the holder is an airsofter. If the venue you go would give him a membership for turning up 3 times in not less than 2 months, and they are on the UKARA scheme, then your dad would get that proof and could buy a RIF that he could gift to you.
Harsh truth is that you can keep shovelling money into it or you can give it to an airsoft tech who understands the details of how things work and will fix it for you.
Plus we are usually far away from normal people using PMR frequencies, so even with higher power, we don't interfere with anything. Probably that's why no one cares.
For extreme lightweight you might try this: https://www.printables.com/model/164853-mosquito-airsoft-kit-open-beta?fbclid=IwAR21DHG2pd7Kju6MgZVn7h4Kkvx4XfUIRZzD0Q9G0cs0X9ANVLV_JZd9CWc
V3 gb and AK hop. Mags are mp5 mags though.
For super-extreme, you can even try it with a plastic gearbox.
As a bush, I say the rules apply to all. If I can wear it on my ankle, the non bushes can too. If I can hide it with my gear, they can too. Then it's a personal choice with its consequences.
I never wear it on my ankle, I'd get friendly fired too much, but I do prefer blue over red.
I do see...
Without knowing the exact parts you have, could be the spring guide is too long. This cylinder might not have enough space to allow it to be pulled back enough.
Or the cylinder doesn't have enough space for this spring and it's fully compressed before it's pulled back enough.
Try if it locks...
If it's not that two diameter cylinder, like the edgi, then there's nowhere near enough air volume for a 0.48g BB and an 550 barrel.
70 hardness rubber is too hard for that weight. The recommended hardnesses are for the measured FPS on the weight you use, not the FPS it would be on 0.20g.