Shorten 16" Carbine Barrel?

[robrob]

I'm probably going to remove the barrel of my Model1Sales 16" Carbine upper and ream it to 300 BLK. While I have it off it would be easy for me to throw it on the lathe and shorten it to around 14" (I have several registered SBR lowers). The gas port is in the carbine position and I always use a suppressor.

Does anyone know if removing 2 inches will greatly affect the gas system? Currently the rifle is feeding fine with 220gr bullets and I have to close up the adjustable gas tube to slow the cycling speed. I was denting the mouth of my brass upon ejection until I reduced the gas.

Thanks in advance,

Rob