If you’re gearing up to build your own AR-15 or AR-10, one of the first decisions you’ll face is whether to go with an 80 percent lower or a fully assembled lower receiver. Each option has its own perks and drawbacks, and your choice will depend on your goals, skill level, and preferences.
In this guide, we’ll break down the pros and cons of 80% lowers versus fully assembled lower receivers so you can make an informed decision and start building your dream firearm.
What’s the Difference Between an 80 Percent Lower and a Fully Assembled Lower Receiver?
Let’s start with the basics.
- 80 Percent Lower: A partially machined lower receiver that’s not legally classified as a firearm. You’ll need to finish machining it (drilling, milling, etc.) before it can function in a firearm.
- Fully Assembled Lower Receiver: A completed lower receiver that comes with all the components installed and ready to use. This option is considered a firearm and requires an FFL transfer for purchase.
Now that we’re clear on what these terms mean, let’s dive into the pros and cons of each option.
Why Choose an 80 Percent Lower?
The Pros:
1. Customization Freedom
With an 80 percent lower, you’re starting with a blank canvas. You can choose every component, from the trigger to the buffer system, to match your needs. Want a competition-grade trigger? Prefer a specific stock for hunting? The choice is all yours.
2. Cost Savings
Purchasing an 80% lower receiver is often cheaper than buying a fully assembled lower. Plus, you can prioritize your spending on high-quality parts where it matters most.
3. Privacy
Here’s the kicker: an 80 percent lower isn’t classified as a firearm until you complete it. That means, in many states, you can purchase one without going through an FFL transfer, background check, or registration.
4. Hands-On Learning
Finishing an 80% lower is a great way to learn more about how firearms work. If you’re the type who loves DIY projects, this is a rewarding experience that teaches valuable skills.
The Cons:
1. Time and Effort
Completing an 80 percent lower takes time, patience, and the right tools. If you’re not comfortable with milling or drilling, it can be a bit intimidating for beginners.
2. Specialized Tools Required
To complete an 80% lower, you’ll need tools like a jig kit, drill press, and possibly a router. If you don’t already have these, the initial investment might feel steep.
3. Legal Considerations
While 80 percent lowers are legal in many states, some areas have restrictions or additional requirements. Be sure to research the laws in your state before purchasing or completing one.
Why Choose a Fully Assembled Lower Receiver?
The Pros:
1. Convenience
The biggest advantage of a fully assembled lower receiver? It’s ready to go out of the box. No machining, no tools, no fuss. If you’re short on time or don’t want to deal with the DIY process, this is the way to go.
2. No Special Tools Needed
Unlike an 80% lower, a fully assembled lower doesn’t require any drilling or milling. All you need to do is attach it to the upper receiver, and you’re good to go.
3. Guaranteed Functionality
Fully assembled lowers are built by manufacturers to exact specifications, so you can trust they’ll function properly right from the start. This is especially appealing if you’re new to firearms or want peace of mind.
The Cons:
1. Less Customization
When you buy a fully assembled lower, you’re stuck with the manufacturer’s choices for things like the trigger, stock, and other components. Sure, you can swap out parts later, but that adds extra cost and effort.
2. Higher Upfront Cost
Fully assembled lowers tend to cost more than 80 percent lowers, especially if they come with premium components. You’re paying for the convenience of having the work done for you.
3. FFL Requirements
Since a fully assembled lower is legally classified as a firearm, you’ll need to go through an FFL transfer, including paperwork and background checks. For some, this adds extra hassle.
Comparing the Two: Which Is Right for You?
Here’s a quick side-by-side comparison to help you decide:
| Feature | 80 Percent Lower | Fully Assembled Lower |
| Customization | Full control over every component | Limited to manufacturer’s choices |
| Cost | Generally more affordable | Higher upfront cost |
| Skill Level Required | Requires machining and assembly | Minimal assembly required |
| Tools Needed | Yes (jig kit, drill press, etc.) | No |
| Privacy | No FFL transfer required (in most states) | Requires FFL transfer |
| Convenience | Time and effort required | Ready to use out of the box |
So, Which Should You Pick?
It depends on your priorities.
- Choose an 80 Percent Lower if…
- You want maximum customization.
- You enjoy DIY projects and don’t mind investing time and effort.
- Privacy and independence are important to you.
- Choose a Fully Assembled Lower if…
- You’re short on time or prefer convenience.
- You’re new to firearms and want a functional product with minimal effort.
- You don’t mind paying extra for a ready-to-use solution.
Final Thoughts
Both 80 percent lowers and fully assembled lower receivers have their place in the firearm world. If you’re the hands-on type who loves a good project, an 80% lower gives you the freedom to build your dream firearm from the ground up. On the other hand, if you value convenience and just want something that works right out of the box, a fully assembled lower might be the better choice.
No matter what you decide, Thunder Tactical has you covered. From 80 percent lowers to complete build kits, we offer everything you need to bring your vision to life. Check out our selection today and start building the firearm that’s perfect for you!