Rattle can woes - any advice please

What kind of model is it and are we talking flat or curved surfaces?

I too use rattle cans - no airbrush and no hope of ever getting one - and if your primer did what I think it did, best bet is to strip the paint off with something plastic safe, if that won't destroy any already installed detail work, or sand with a fine grit pad (600 or higher) to smooth things down. Otherwise, yep, you probably will end up with a gently rolling to bumpy finish.

Other considerations: Was it humid when you were spraying outside? (I hope you were outside!) If so, that can cause pebbling or other unwelcome results. Did you shake the can up thoroughly before and during the spraying? If you were using the semi-gloss Testors gray primer, heating the can up in a pan of warm (NOT hot) water before you start can give a smoother coat.

It sounds like several problems may be present. When an aerosol can stops suddenly, it usually means that there is a large particle of something stuck in the spray head, or that the can is well past its expiration date. Most rattle cans tell you to shake for two minutes—that is a minimum! In the paint lab, we shake for at least five minutes, varying the motion periodically. This is especially necessary for a can that has been sitting for a long time.

You can try to clean out the spray head. Gently pull it from the valve in the can. You will find a very fine slit in the down-tube. Run your finger through that, and inspect the inside for a clog. Washing it out with the appropriate thinner and a pipe cleaner may help. When clean, gently twist it back into the valve on the can, KEEPING THE SPRAY ORIFICE POINTED AWAY FROM YOU. Shake for five minutes (consider that this is good aerobic exercise). Then try it out on scrap.

As for the model, you can also sand the primer after it is thoroughly cured, rather than striping it completely. This is probably less work and less hazardous to you and the model. Since you want a very smooth, glossy finish, I would sand the primed model progressively from 800 to at least 1000 grit. Use a light touch.

 And heed the mfsob's advice on getting the best performance from an aerosol can.

Thanks for the advice,
sounds like I've got some work to do :-(

The model is the drone that came with the Revell SR-71 kit. I've only been modelling for about 2 years and there are some areas where I need to get some focussed practice and experience.
Seams and gloss paint were two areas that had been high on my list for a while - and after a quick look for something "easy" but requiring seam work and with a mix of flats and curves and very few detail pieces the drone looked to be a good choice. Then the primer problem - ah well I wouldn't be modelling if I didn't like a challenge from time to time!

Thanks for the advice on the rattle can handling - I'd been reading up (and have done some rattle work before) so I'd warmed and shaken before use (my normal routine is to shake while dead heading the plants in the garden, warm in water while drinking a coffee, then shake while de-slugging the salad beds) before heading into the garage (British garage - so think draughty wooden shed full of junk) to spray. The lumps definitely result from not getting sufficient paint down to allow it to fully cover the plastic as I had primied a Helo before switching to the drone when the rattle can gave out and the Helo looks fine. (oh and it was definitely a warm dry day as I don't go near the garden under any other conditions.)

The rattle can had been sitting for a while before I used it, it was about a year old from the store and about half full. But it was given a very good shake, there's still content in there so I guess there is something solidly lodged in the spray mechanism. Triarius, Thanks for the advice on trying to clear the blockage. I haven't been able to clear it, so the can is on its way to the dump.

mfsob, I'm trying to stay away from strong chemicals :-) so I'll go with trying to sand the primer clear - it'll help that the drone has no awkward areas for sanding. I wasn't sure if it was worth attempting or if there would be an inevitable bumpy finish, but I guess I could end up sanding right back to the plastic. I'm investing in some fine wet-n-dry and blocking a couple of days in my diary.

Thanks again for the advice