Just curious here, but what makes you believe that there is room for improvement based upon 6 grams per 2.5 ounces?

I am really not in to BHO, so I don't have much advice, but I strongly recommend vacuum oven purging. Yes, they are expensive, like $1,000 an up!

The air bubbles in shatter probably contain butane.

There is one thing that I can advise that may help improve your product. Put your butane cans and your prepared tubes in the freezer for 48 hours before conducting your extraction process.
GrowGoddess Reviewed by GrowGoddess on . MAKING BUTANE HASH COMPLETE WALK THROUGH PLEASE I've been making some butane hash for awhile now with power 5x butane in an extraction tube made out of glass and I feel like it's just not as good as it can be. This is the process I've been using and if anyone has any advice or pointers PLEASE do share! Our tube holds 2.5 oz that we grind up and stuff in leaving about 1/4 of an inch empty, we're using about 60% nugs and 40% trimming and it's probably B to B+ quality pot. We are using about 3 cans of butane which hold 5.5 oz of gas each. Rating: 5