kasaran

room temp and shaken well, the missus (having a history with spray cans) did the base coat and found them to be bad.  oddly enough, the brown one was better, the khaki/tan one was the trouble maker.

As with any paint job, the result is only as good as the prep work you put in.

Ask any paint shop tech, they spend most of their time in prep of the piece to then spend a fraction of the actual time a job takes to put the top coat on.

Also the surface you are applying the paint to, even with self primers, unless the proper primer coat is used to bond with the substance you are painting, then any job you do will likely be looking like your underwear after a blow out with the lads and that curry resurfaced rather prompt like...

Do you know what you are painting? Some metals do not take a paint job well unless they have been properly painted with a base primer that is able o etch in and give a bonding layer. Some polymers will not take certain types of paints. That will not be down to any polymer, it could be that manufacturers blend or that batch may have a different blend of chemicals. 

Many reasons exist for a paint job to not come out well, including operator error and how that operator applies that paint.

Judging from your comments, my main points address what you are likely having a problem with... its not likely the paint and if you say you did the job right then its not you, leaving the only thing left... the piece you are working on.

Have you thought about asking the manufacturer about paints that will bond?

Surprised to see people defending nuprol paints...  the criticism being that having used TTCombat and more often Tamiya spray paints (which are worth the extra bob), the Nuprol stuff comes out inconsistantly, thick and very watery.  It is sold as suitable for metals and plastics and being Nuprol it will be aimed at the airsoft market whereas the others target model builders.

oddly enough though, the finish i got was actually pretty good, and it was certainly the tan/khaki can that was the worst culprit.  But for ease of use? spend the extra few £.