Are all AR15 lowers the same?
The short answer is yes. All AR15 lowers house the necessary components to, once married to the remaining AR15 parts and loaded, deliver rounds down range. But, that is kind of like saying “are all watches the same?”. They tell the time, don’t they?
The first thing to consider for price and function is Billet vs. Forged receivers. The material that most AR15 receivers are made from is an aluminum alloy called 7075 T6. It has similar qualities whether formed into a billet and cut or forged into a receiver shape and finished; the only difference is how it is processed. Billet receivers start as a forged rectangle of aluminum which is milled into its final shape. Forged receivers come out of the forging process looking more or less like the finished product. Generally speaking, billet receivers are more expensive, stronger (specifically where you want strength) and more custom (how it looks). You can also buy billet receivers that have been "matched" to a billet upper for the ultimate fit. Having said that, modern manufacturing processes have created very tough and good looking receivers with little to no increase in cost.
Now that you have your lower how much assembly do you want to do? Most companies sell their lower receivers “Stripped” without any controls, pins, springs, etc. This is generally the cheapest way to buy a lower and allows for selecting components based on cost, function, or some other criteria. Alternatively, many receivers can be purchased as “Partial” or “Complete” lowers with all the parts installed. Complete lowers may have inexpensive “mil-spec” parts in them or ship with all the “bells and whistles” like ambidextrous controls, short throw safeties, oversized bolt catches/releases, oversized mag releases, fancy stocks and top of the line triggers. It is very possible that the parts package is more valuable than the receiver itself. A fact that greatly impacts the cost.
One last consideration is brand. While it may have nothing to do with function and reliability, the brand does impact the value of an AR15 receiver for sale and resale. Whether the increased cost is warranted or not, the brand value can’t be dismissed.
So, are all AR15 Lowers the same? Look at your wrist… Are you wearing a Timex, an Apple Watch or a Rolex? They all tell the time, don’t they?