I used an image plane as well as about 5-10 different photographs of AK-47s for my AK model and I'm really happy with how it turned out, can't wait to get it textured. Never could find a decent hi-res image of the iron-sights though, so there's a little bit of guess-work going on there.
It might be hard to imagine seeing me cut all of those corners in the vids but when I sit down to do a proper model which I intend to use for something productive I do use reference, I do clean the topology and I do take my time with the details. The speedmodels are just for a bit of fun

Martin.