Changing buttstock on Norinco 311

[spartan1980]

trying to change the buttstock on my 311. I unscrewed the old stock and pulled it off. there is a long pipe which is attached to the lower receiver (and ran through the old buttstock). my question is, should this come off too? I tried pulling on it but it wont budge. without removing it, I cannot put the new carbine stock on?

anyone tell me what i am doing wrong?

 

[Striker]

That is the buffer tube. It's screwed into the lower receiver.