Question that's been bugging me the manufactures directions just states a urethane adhesive when I go to titebond or bona website they have the big pails to use a trowel with I am going to nail down and would like to use a chalking gun to spread adhesive but everywhere I look I only seethe big buckets for trowel or the messy sausage tubes why don't they sell flooring adhesive in the normal tubes while on the topic why can't I use regular construction or subfloor adhesive... I'm using 9 in wide plank engineered flooring... Thanks in advance

Regular construction adhesive holds very well, but wood floor adhesive needs to be able to hold and still flex with seasonal movement without braking the bond. I use sub-floor adhesive when I get close to the walls so I can finish with minimal top-nailing when too close to the wall for blind nails.
The sausage guns are practical and relatively cheap. This style of gun is bigger than the tubes for a regular caulking gun. You can get wood floor adhesive in the sausage type tubes. Sausage tubes aren't messy, in my experience.