A quality barrel is the most crucial component. If your upper is complete, the quality of the components used will determine how reliable and accurate it will be. Reliability and wide compatibility make a desirable combination. Others work best with lowers from the same company. Compatibility is a major concern when choosing one some models are calibrated to work with the widest variety of lowers, but still require verification. The particular alloy of aluminum used to manufacture the receiver is less crucial with a 9mm upper than with standard ARs thanks to the lower pressures. Even specific models can be more proven and esteemed than others. The first thing to look for is an product made by a reputable, well-established company. To some degree, the best 9mm AR upper will depend on your preferences. The complete variety, on the other hand, are ready to drop into your lower immediately-cock, lock, and rock and roll. The stripped variety gives you the opportunity to customize all the components you use to build your firearm. However, the main distinction among 9mm AR upper receivers is that between complete uppers and stripped ones. This can be more rigid and accurate, and also looks a lot cooler. This means that the handrail integrates seamlessly with the upper. Some are monolithic or mimic the monolithic style. However, machined receivers are CNC cut from billets of aluminum alloy that were originally forged anyway.

There is an idea that forged receivers are stronger because the forging process slams the molecules of the aluminum alloy into alignment. Upper receivers come either forged or machined. These features are less useful with the 9mm, anyway. Smooth side receivers are lower profile than standard and lack the protrusions common on ARs like a shell deflector and forward assist. This is why building such a firearm can be so rewarding. There are a wide variety of customization possibilities when selecting a 9mm AR upper receiver. Gas block front sights are less common than on standard ARs. Rear sights are usually not included, while front sights are hit and miss. Forward assists are less common on 9mm uppers than they are on standard AR receivers.Ī dust cover is also an optional item. Charging handles come in a number of varieties, including classic M4 and non-reciprocating. Inside, there will be a bolt carrier group. First, there will be a barrel with a gas system and handguard.

9mm ar upper receiver stripped