First of all, are these guns all exactly the same?
They look exactly alike but with different finishes.
Second, if they are different, how and which one is the best?
And third, I know that the barrel on the Raider cannot be removed, but what about the other guns? and are there any other upgrades for them?
Yep, they are all alike with different finishes. Pretty much makes them all equal. And I'm fairly certain all of those 4 particular models have non-removable barrels.
They "different name for each color" thing was quite common with Brass Eagle and Viewloader. The black VL Revelation was nearly identical to the blue VL Triton 1, which was identical to the red BE Avenger. The red BE Avenger 2 was identical to the grey VL Vertex. And on and on and on.
No upgrades made specifically for those guns you listed, but if you're creative and handy with some tools you can come up with a few things.
There's even a 5th one, the marauder 2. This is the only one to have a removable barrel. I think it's kinda rare as far as BE's go. As far as upgrades, get the BE vertical adapter for an expansion chamber. Helps a bit.
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