My preferred drawn 6060 aluminium tube, 12.7mm OD, 9.85mm ID, is only 748 grams for a 5.5m length, making a 3ft blowgun weigh in at around 136 grams, a 5ft approx 163 grams, not much more than PVC at all.
I like my blowguns at 5 foot and pvc sags.....ive tried the sliding over technique but I could not get the 3/4 to slide far enough down the 1/2.....BUT I have found the cure!!!!!! lubricate the outside of the 1/2 with petroleum jelly. do NOT lub the inside of the 3/4 of it will catch fire when heating!!!!!!! hope this helps