80 Lower Receivers

Modulus Arms 80 Lowers Features

Modulus Arms’ 80 lower receivers are distinctly noticeable for their curved design in the magwell. This was an intentional design aimed at reducing weight but still able to reliably seat and load in magazines with the flared magwell.

Our 80% lower receivers have full mil-spec parts compatibility with classic fire/safe markings engraved. These lowers are incredibly tough as they’re made out of aerospace grade aluminum. The color options include a mil-spec Type III hard anodized black and a raw finish for those who prefer to Cerakote, DuraCoat, or spray paint their own colors and designs themselves.

Why is it called an 80 percent lower?

Curious about the term "80% lower"? Let's break it down:

Unlike a complete firearm, an 80% lower is 80% finished, with the remaining 20% to be accomplished by its purchaser. This often means precise machining of specific parts to make it fully operational.

Constructed from sturdy materials like aluminum or polymer, 80% lowers start as solid blocks. Using tools like the router jig extreme, enthusiasts can seamlessly complete the remaining portion. Once essential elements, such as the trigger or safety mechanisms, are integrated, it transitions from an 80% lower status to a legally recognized complete firearm.

In essence, the "80% lower" phrase signifies its state of readiness, offering builders an opportunity to remove the remaining 20% of the lower. For more details and insights, contact us!


 In the firearm landscape, the 80% lower has emerged as a powerful representation of self-reliance, customization, and practical know-how. Here's a look at why you should consider building your own, especially in today's times: 

  • Full Control: When you build from an 80% lower, you're in the driver's seat. Every part, every detail, is under your command, ensuring you get exactly what you want.
  • Mechanical Insight: Get to know your firearm inside and out. Building from the ground up deepens your understanding of its mechanics, which can be crucial in critical situations.
  • Tailored Customization: Why settle? Constructing your own allows for unique modifications suited precisely to your preferences.
  • Regulation and Privacy: One of the compelling reasons many choose to complete an 80% lower is the privacy it offers. Since 80% lowers are not considered firearms until they're completed, they don't require an FFL (Federal Firearms License), provided all federal and local laws are adhered to.
  • Skill Acquisition: It's a straightforward task with an 80% lower, but the skills you pick up—precision drilling, milling, and finishing—can be applied elsewhere.
  • Be Ahead of the Curve: With shifting regulations and market uncertainties, there's no telling where the future of firearms is headed. Secure your capability to build and customize by diving into 80% lowers now.

Simply put, if you've ever considered building your own firearm, there's no better time than the present. Equip yourself with the skills and knowledge, and ensure you aren't left wishing you'd acted sooner.

What are the laws for 80% lowers?

Although 80 lowers are still not defined as firearms on the federal level and by the ATF, state laws all vary. The degree to which they are deemed legal and illegal is a wide spectrum with some states even banning parts or related tools. If any of our products have shipping restrictions you’ll see the list of states that we can’t ship to in the product description. 

Do you have to put a serial number on an 80% lower?

It depends on the state that you reside in. Some states will completely ban the legal possession, ownership or act of manufacturing your own firearm so that’s moot there. However, states that do not restrict this right will typically have some legal verbiage that states something along the lines of — as long as you make this item for personal use and not for sale or distribution, it can be legally permissible.

There are also states that do not completely ban the activity of making your own guns but if you do choose to do so, you must remain compliant by applying for a unique serial number with your state’s DOJ and get it engraved onto your 80 lower within a set timeframe. 

Can 80 lowers be a pistol?

80 lowers exist in the form of AR lower receivers and pistol frames as well. Once you build them out they certainly could be a pistol. Whether it’s an AR pistol, Glock-style, Sig-style or 1911 style there are many types of 80 lowers available for builders today.

Lifetime Guarantee

Modulus Arms offers a lifetime replacement warranty for all of its 80% lower receivers so you have a product guaranteed for life.

Legal Disclaimer

Please understand that we are not lawyers and the information here is not presented as legal advice nor should it be construed as such. The content of this page is strictly meant to inform. If you need legal advice please consult an attorney. Laws change constantly and we make no promises that the information below is or will remain accurate. To protect your freedom, you must do your own research.