When you are assembling your AR-15, one of the last things you want to find out is that you made a mistake with the assembly and your AR-15 doesn't operate the way you intended it to or not at all.
Sight Your Rifle
Always make sure to sight your rifle regardless of whether you use a 25-yard zero or a 50-yard zero. If your rifle is not properly sighted and you miss and hit a bystander while acting in self-defense, you may face liability issues.
Leave the Ejection Port Closed
Do not open the ejection port. Some AR-15 owners will open up the ejection port to create more room for loading and unloading the rifle. The problem is that the individual opening the port often removes the riding surface and will jeopardize the accuracy of your rifle.
Use the Right Buffer
Do not install the wrong buffer. You have many aftermarket buffers to choose from, but if you do not use the right buffer, the bolt carrier will cycle back too much and the carrier gas key will become the stop for the carrier. In some cases, the gas key will even snap off and render the rifle inoperable. Even if this doesn't happen, the wrong buffer will affect the accuracy of your AR-15.
Don't Keep Your Rifle Dry
Always remember to lubricate your rifle. Dry rifles are rarely competitive and can also be less effective in a self-defense situation. When shooting about 30 rounds, your AR-15 may function perfectly fine. But the more you use your rifle, the more likely that it will malfunction.
Understand Your Objectives
Build your AR-15 based on the goals you have in mind. There are some parts that are more well-suited for one purpose than for another. Do you need your AR-15 for self-defense, or is your primary objective to go hunting? Regardless of the purpose, do not purchase cheap parts, but you should instead focus on purchasing the best parts for the purpose you will use the AR-15 for, regardless of the cost.
Buy the Best Parts
Always use high-quality parts, such as the Mil Spec Nickel Bolt Carrier Group. Rifles always need to be manufactured to very strict specifications to be able to function properly. By purchasing your replacement parts from a respected vendor, you'll feel more confident regardless of whether you engage in competitive shooting or are using an AR-15 for self-defense.