3M PPS Accuspray System
When I was priming during my -14 wing build I tried several methods.
1st thing I would say is to prep the material well - it must be clean, clean, clean.
Acetone, soctch-bright pad, Prekote, scotch-bright pad, rinse, use gloves, and make sure everything is dry. If you do this your 90% of the way there.
PPS have several different size cups, all disposable, and self measuring. The tips are clear so you can see when it's clean without taking it apart. I like mixing up just enough for the job, it's usually just a few small parts at a time, so the 6 oz cup works great. I have a few disposable syringes from my Pharmicy that I use to measure the product since tipping a gallon can to pour is hard for me and I end up with more product on the bench than in the gum.
I used a regular spray gun with the quart jar, it works fine, but cleaning is just a pain.
There have been several threads about Accuspray PPS, with links, check them out. That's how I found out about it and highly recommend.