I'm curious about the Cometa Fennix 400 and really just wanted to know how it compares to Diana, German Beeman and Even Gamo Bone Collector? See what I'm looking at for next purchase. 

I'd like a springer or gas ram that is accurate to 50 yards and has some power and is of decent quality. Currently have a Swarm Magnum Gen 2 and it shoots 4" in one direction and then 4" in the other direction on the next shot and that's at 20 yards. Must be defective since my Maxxim can stack at that distance.Cometas blow Gamos out of the water. If there was justice in this world, Cometa would be the household name in Spanish airguns.
That being said, comparisons always need the qualifier of what you are looking for in a gun. There is NO springer that fitted everyone, and preferences vary widely. So, tell us what you want in your next gun and we'll go from there.
To me, Dianas are way better guns than Weihrauchs - more accurate in .22 cal, actually shooting up to spec, covering more range in the upper power zone, easier to tear down, just as durable & dependable etc.
Cometa 400 is excellent for the money they used to be, best trigger in the price bracket, very handy dimensions etc., but too lively and aggressive in factory form (due to low mass, loose guides and relatively high power), and the mainsprings are really short-lived due to being under-sized (ID) and overstressed. They are a mid-power gun.
When you need accurate, dependable 24 fpe, Diana is the only game in town these days, unless you fancy an over-pressurised HW90 which costs some 50% more and is a burden to cock.
But each shooter has different needs / wants.
The Swarm mechanism is probably clipping pellets. Try removing it and loading the pellets manually. I did that with my gen3 and it improved performance significantly. I'm not familiar with the gen2, but they were infamous for that.I'd like a springer or gas ram that is accurate to 50 yards and has some power and is of decent quality. Currently have a Swarm Magnum Gen 2 and it shoots 4" in one direction and then 4" in the other direction on the next shot and that's at 20 yards. Must be defective since my Maxxim can stack at that distance.