Would cutting a barrel down 6" effect the cycling on an AR?

The gun is a factory 22" rifle length gas system

If i cut the barrel to 16" will it still function properly with a rifle length gas system?

Or

Will it function poorly?

Can't go 16" on rifle length gas without making some other mods for it to cycle. 18" shouldn't be a problem.

^^yup

Why not just trade off the 22" upper for a 16" one? Then it should work just fine.

cutting one down, when there are thousands at the length you want?

sell what you have, buy what you want

don't cut it down

DPMS used to sell a rifle gas 16" It worked quite well, but I think gas port was probably opened up. It should work fine, but will likely need a bit more gas.