Posted by on 3/4/2022 to
An 80% lower is a lower receiver blank, in the shape of the lower receiver without certain holes and a serial number. An un-finished 80% lower cannot accept a trigger, hammer, or safety so it cannot be used as a firearm until the modifications are made. Maybe calling these 80% lower receivers is a misnomer since they actually have more material than they should. Perhaps we should call these 110% lowers where you drill out the extra 10% of material to create a 100% functional lower receiver. It was decided however that it made more sense to call the 80% since they are 80% of the way to being a 100% fully functional lower receiver.
80% lowers are made in every major style of firearms, they can be as varied as any full lower receiver out there. In fact everything that applies to lower receivers also applies to 80% lower receivers. Rifles and pistols, AR-9s. LR-308s, and of course AR-15s. With pistols, there are Glock compatible and Sig Sauer compatible 80% lowers. These lowers tend to be made with the material you would expect from the typical lower. Many of the pistol 80% lowers are polymer though there are aluminum versions. Conversely, the rifle 80% lowers is mostly aluminum with some polymer versions. The aluminum versions will either be raw, unadorned aluminum, or anodized, a process that strengthens the metal as well as gives it color.
Once you get your 80% lower you need to make the changes necessary to get it working. Many of them are sold with a jig that fits over your piece and has holes of the correct size and in the correct place. With the jig in place just drill with the appropriate sized bits and you're done, nice and easy. Some kits will even give you the right drill bits to make it even easier. If you plan on doing a lot of 80% lowers you can get an adjustable jig that will work across multiple platforms.
Since 80% lower receivers are simply unfinished everything that applies to lower receivers applies to 80% receivers. Is it polymer or aluminum? Forged or billet? 6061 or 7075? All the same choices, the strengths and weaknesses you might find in a finished lower receiver you can also find with 80% lower receivers.
So why is an 80% lower receiver a good choice for you? If you want a fun project that produces a firearm then 80% might be the right choice. It is often cheaper due to it being unfinished so it may be worthwhile for you to put in your labor for a lower price. It will give you more knowledge on how your firearm works, which can also help if you need to repair it. Buying and working on an 80% build can be a fun project that will teach you more about your trusty firearm.