First game help
 

The field I'm playing on has a fps limit of 420. And my gun is shooting 415 to 435. Would it still be allowed to play?

Entirely up to the venue staff, I would probably say no because its a safety hazard, since it has a much higher upper range than lower range and insurance is expensive so business may err on the cautious side.

Likely no, 420 is probably their hard cap. It doesn't matter, if your gun is over and/or that inconsistent, then it'll need a change regardless at some point. Get it to a gun doc and get a spring swap so you can play (many stores have docs and springs), or make arrangements to borrow/rent a different gun for now.

Or you could put a velocity reducer on the barrel as a short term solution

just assume no, 420 is already pretty high. Not that kind of high but velocity type of high. you better modify your gun before you go to the range. I do not know your type of gun but I assume that if you want to avoid opening your gearbox, getting a shorter inner barrel should do the trick for you.

Normally fields will give 5 - 10 fps variance max. That being said most 420 fields have that as a hard cap with 400 ish being the actual limit.
That being said, the easiest/cheapest way to reduce your fps would likely be to swap the inner barrel. Aside from that even just taking it apart (the hop up and barrel) and cleaning it and reassemble should help your consistency issues. After that actually using it for a few thousand rounds should settle the spring but maybe not by ~20fps that you need to be safe.
Edit: if you have the tools. Either a lathe or pipe cutting tools, you can just cut your own barrel. If you have "cnc" stuff you can port the barrel. Technically you can just cut it with a hack saw (gently and slowly) and then use a reamer on the end or even just some sand paper to finnish off the crown a bit in case of any edges.

Why don't you ask the field, instead of asking people to guess.