There are many styles of Barrel contours, or profiles, and a lot of them can appear similar. It's also not always clear why certain profiles or contours are designed the way they are. Sometimes the answer to the latter question is as simple as quote: the barrels were bending when soldiers were using them to pry open crates, so we made them thicker on the end. Seriously. That's the reason behind the extra material at the muzzle end of a M16A2 rifle barrel according to Eric Kincel of Bravo Company USA. When it comes to selecting which barrel profile is right for you, consider the performance demands you'll be putting on your rifle. A heavy barrel, sometimes denoted as an HBAR barrel, will lack the various changes in thickness along the length. Most will have two different thickness radii, with one transition point somewhere in between them. These will be the heaviest to carry, but also will heat the slowest, keeping your accuracy truer for longer. The vast majority of AR owners will never shoot enough ammunition fast enough to need a heavy barrel in the entire time they own the firearm. Lighter weight barrels with contour types such as government, gunner, tapered, M4, SOCOM, and Pencil, will be perfect. You can find some of our best here. Some manufacturers will even have proprietary profiles that are engineered to combine some great characteristics of many different contour types. The biggest advantage to these lighter barrels is the decreased weight, which can be crucial if this is a rifle you'll be carrying for long periods of time. Common features found on many barrels today are processes used to reduce weight through fluting or dimpling. These barrels will have long, shallow sections of removed material, or small circular pieces of material removed from the surface of the barrel. As cool as this looks, these are not merely stylistic features. These processes allow for weight to be reduced on heavier barrels, and increase overall surface area allowing for better cooling.