Long time viewer first time poster

[customcutter]

I would rather have a tight upper like yours than one that is loose. But, your problem is wanting to disassemble. If/when you heat the upper, don't use anything hotter than a heat gun. No open flames our you could damage the heat treating on the upper. I could be wrong, but I think you'll find more thermal expansion by heating the upper, than shrinkage by cooling the barrel.

Edit:

You might want to measure the barrel extension and upper too make sure that both are within spec. It is possible to be in spec and be this tight, .0003" to be exact.