There’s quite a lot of misinformation floating around about how 80% lowers and finished lower receivers are made. Let’s clear some of that up with a nice breakdown and comparison of the three primary methods of construction: Billet, cast, and forged.
There are pros and cons to each method, and when it comes to finishing your own 80% lower, these differences may matter a bit more – but we’ll start off with saying that none of the three methods is dramatically different than the others. Let’s get into how each is made, first.
How a Forged Lower is Made
A forged AR 15 lower is made by hammering two roughly shaped halves of a receiver together, forming one whole unit. Once forged, the whole unit is deburred and cleaned up to ensure no inconsistencies are present in the finished lower. This forging process is considered “mil-spec” – it’s what the U.S. Military requires of its manufacturers when they buy new rifles. Forged lowers are generally said to be more durable and rugged. The forging process creates a denser aluminum alloy and it orients the metal grain structure.
Our 80% Forged Lower is one of the most well-built, popular lowers available currently, featuring a rugged 7075 T6 construction
How a Billet Lower is Made
Billet lowers are cut as one, solid receiver from a big chunk of aluminum alloy. First, the lower blank is very roughly cut from a large block, and a CNC machine, input with specific data and cutting measurements, goes to work – usually for a few hours – cutting out every single angle and hole the receiver needs to be finished.
Our Premium Billet 80% Lower is the easiest lower to finish, a great choice for first-time builders! A flared mag well and threaded bolt catch and rear takedown pin holes make building and operation simple.
Billet lowers allow for more fancy designs and variations in their finished dimensions. All those skeletonized lowers and flared mag well lowers are made from billet manufacturing.
How a Cast Lower is Made
Okay, so this is the only time we will give a strongly worded opinion on anything related to rifle building: Do. Not. Buy. A Cast. Lower. Ever. They should be avoided like the plague. There are no inherent benefits in building an AR 15 using a cast lower, though there are plenty of inherent deficiencies: Cast lowers are less dense, less precisely manufactured, and are weaker than billet or forged lowers.
They super-cheap, and when it comes to guns, you get what you pay for. You should never approach any rifle with the mindset of trying to spend the least amount of money possible, sacrificing quality and safety. Cast lowers have literally exploded in their owners’ faces. You don’t want an exploding AR 15.
So, Which Lower is Best?
In truth, neither. What matters most is the aluminum alloy each receiver is made of. There are two popular alloys used in receiver making: 6061 and 7075. The former uses less zinc and is generally more machinable. If you’re a first-time 80% lower builder, we recommend sticking with this alloy for your first go at it.
7075 aluminum is a tad harder and less machinable. It provides a slightly more rugged lower that might be less prone to small dents and dings. Today, both alloys are so precisely created and 80% lowers are so well crafted, that it makes little measurable difference in truth. Both will last a lifetime, both will stand up to the rigors of the field, and both will handle tens of thousands of rounds. Now you know!