9mm AR upper question

[koxx.dta]

Not sure if this goes here pistol or rifle but anyway my question is, can I use a standard ar-15 stripped upper receiver to build a 9mm ar or do I have to use a 9mm stripped upper. Basically my question is how will the gas tube hole affect a 9mm upper as far as operation. Thanks in advance and for all the help in the past

 

[backbencher]

The gas tube hole doesn't affect anything if there's no tube in it.