Little more complicated then that. I was out of personal transfers so would have had to use a dealer anyway and I needed to fund another project prior to 1/20/21.
My point is this classifieds isn't a good litmus test of fair market pricing.
I had my M&P .40 for sale here for a long time and got no bites for a good price of $500. So I took it to Gun Parlor and got $400 for it.
They sold it to some fu cking sucker for $700 in 24 hours.
The classifieds here are limited penetration with ma gun owners
Sounds like your gas tube is misaligned and jamming up the charging handle.
With all due respect building an upper is stupid easy. Not sure why you didn't YouTube it and go about it on your own. Pm me if you want to chat. I've built many uppers and they all run 100%