I suggest that you hardly ever scale your models to real life. Remember that Blockheads are short and stumpy so the models should be too. If your making a long model, like a sniper rifle, the long barrel really shouldn't be any longer than the length of the blockhead. Also, when it comes to cylinders, try to limit yourself to octagonal or hexagonal ones. And avoid smooth shading.
Don't take the criticism too hard. My first models were awful.