Obtaining a golden skin for your favorite gun in Modern Warfare will require you to complete a variety of different tasks, although most players find that landing longshot kills can be the most tedious. Luckily, there's a fairly simple way to rack up over 100 of them in less than a few hours.
First, you'll want to make sure that hardcore mode is turned on, ensuring that enemies only take one shot to take down. Then, select a multiplayer playlist that gives you the best chance of playing on the map, Shoot House. This is easiest when the Shoot House 24/7 playlist is live, although any playlist that features small maps can work.
The rest is fairly simple. Head to either end of the elongated middle section of the map. You may often see snipers camping here in order to kill players that wander into this section. Simply sit here and try to take down every player that crosses your sights. Given that you're in hardcore mode, you'll have a fair chance at taking out snipers on the other end of the map as well.
Although this method might not be the best for your K/D, doing this for a handful of matches will easily rack up longshot kills. Before you know it, you'll have that golden skin to let everyone know that you're a force to be reckoned with.