You'll have to check reality in at the door when watching a superhero movie. We'll have to assume that the grade and thickness of the heat treated hardened steel Tony used for the suit will in fact stop everything they threw at him from 7.62mm to .50 caliber, which in reality would work. Then we have to assume that all of those bullets were standard ball munitions and not sabot rounds with armor piercing capability (typically tungsten or steel core bullets). To simplify, the inherent properties of the hardened steel, the terminal velocity of the bullets, and the make up of the core bullet material are all significant factors in the suit's ability to provide adequate protection. If Tony were using 1 inch thick cast iron steel, then poor Tony would be hamburger meat under all the perforated armor. .50 caliber would've certainly severed limbs and essentially ripped his body apart very violently. So for argument sake, let's assume that Tony's suit, which was made from salvaged material from his own weapons and munitions, was of superior grade steel or some other super hardened metal alloy and could effectively give him Superman-like man-of-steel protection. The mobility of such a suit then becomes a significant factor, as it would probably weigh at least a 1/4 ton. We're also assuming that the suit's mechanical drive system powered by the arc reactor had enough juice to move all that heavy metal around with relative ease. All in all, very plausible if something like an arc reactor was reality rather than fiction. But I'm not sure what was protecting the arc reactor itself. Ballistic glass perhaps? Looking at the Hot Toys Mark I, the gaps in the armor aren't as apparent as those on the maquette, which is another reason why I'll probably be more than content with the 1/6 scale poseable figure. As much as Tony got shot up, you'd think at least 1 round would have found a way in.
From the images shown here, the Sideshow maquette does seem to have a bit of excessive leg exposure. Perhaps if it were more like the concept images...