Practice drawing some modern weapons like the G36 and the P90 first. Weapons that are made of plastic are usually easier to draw then the old-style WWII type guns. I know you don't know a lot about guns or projectile weapons in general, but since I'm gonna be a regular cilent you might wanna do some research before really diving into those types of projects. Practice using a ruler to draw harsh angles and fine details of firearms. You may have organics down but I notice you lack skill with drawing machinery. You have to approach drawing machines in a different way; they aren't flowing, curvy, and (well) organic. They have sharp angles, turns, stamped parts, and are difficult to draw without a straight edge. I found it hard to transistion to drawing organics when all my life I drew tanks, guns, and fighter jets. Remember: Organisms=Curvy, Flowing. Machines=Angular, Harsh Directions.