different upper configurations?

[chaz]

I was curious the benefits of having multiple uppers is other then "looks"?

[EOD Steve]

Any number of things, depending on who you ask.

Tactical - different uppers allow for different configurations of lighting/peripheral packages (ie: white light vs. IR; different grip = stance configurations); different optics choices without having to re-zero the sight
Performance - different uppers allow for different outer/inner barrel lengths or possibly the user of a suppressor. Depending on barrel length, you can go +/- 50-60fps, yielding an indoor and outdoor setup with the same lower receiver, sacrificing obviously some volumetric efficiency in one of the setups; Beyond just and FPS differential, users may opt to have a CQB upper and a "DMR" or even a support upper with a precision barrel group being applied in the case of the DMR role.

So the idea of hot-swappable uppers goes far beyond just aesthetics, although most people just run multiple guns due to the scarcity of spare upper receivers.

[Cobrajr122]

I have a 20" upper and a 10" upper for my P* M4.

20" is for outdoor games and 10" is for indoor games / games that have indoor elements.

[ThunderCactus]

I have two complete guns that swap uppers
One is a 10.5" MK18
it has the exact same range and accuracy as
The other, a 16" SR15 (that has a 14.5" barrel)

I still use the SR15 in CQB, just because it's my favs.
The only real difference between the two is the length for maneuverability.
For swapping NV/visible light options or optics, I used to have QD mount light packages and have a QD mount optic, so everything is easily transferable between the two.
Really the only reason I swap uppers is if a lower or upper is acting up lol