Quoted:
I asked something like this. From reading other threads and what I was told from members here follows––-Get the stamp first to be safe. You can legally buy a barrel under 16" but if you have a lower that does not have a stamp then you can be charged just the same as having a complete rifle. Now if you have a pistol lower this is diff. Again you can buy the barrel and let somebody who doesn't own an AR or somebody that has an SBR already hold the barrel until yu get your stamp. I had an upper awaiting my stamp thinking as long as I never had it on an lower I was GTG. I was clearly told this was not so and I no longer have that upper in my control. I want to buy a 2nd SBR upper but will now wait until I get my lower's stamp until buying it.

And just to add...the upper I had bought but no longer have was bought as a whole upper that I did not build and was never mated to a lower. Just want to be clear I was not tyring to build an illegal rifle. Just had the procedure wrong that was corrected already.