Nov 30, 2019

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Mil Spec AR-15 Lower Parts Kits

The AR 15 Lower Parts Kit or as it’s better known acronym “LPK” is necessity when building your own AR from an 80% or stripped AR lower. The standard mil-spec Lower Parts Kit typically consists of 32 small parts. These parts make up the trigger, safety, magazine catch/release, pivot pin, bolt catch, pistol grip etc. Basically everything you need to finish the AR lower except for the buttstock and recoil system.

These LPK’s are great for getting your AR-15 up and running and as spare parts. It’s important to note that the triggers included in these kits are the same heavy pull triggers that ship with a majority of factory AR 15 rifles and are simply meant to get your rifle to go “bang”. The pistol grips are nothing special and the same grips that have been used for decades on the M16, M4 and AR-15.

You might find the more time you spend working on AR’s the more “extra” lower parts you end up with. My own experience has lead me to purchase a small Durham brand part# 107-95-IND compartmentalized storage box for the sole purpose of organizing lower parts. I am at the point where unless there’s a bargain I only the exact parts I need from Brownells and I maintain an inventory in my storage box. Tip it’s sometimes easiest to locate these parts by starting at Brownells schematic pages for Colt AR & Sporter and DPMS Rifles.

  • Front Pivot Pin
  • Front Pivot Pin Detent
  • Front Pivot Pin Spring
  • Rear Takedown Pin
  • Rear Takedown Pin Detent
  • Rear Takedown Pin Spring
  • Magazine Catch
  • Magazine Catch Button
  • Magazine Catch Spring
  • Safety
  • Safety Detent
  • Safety Detent Spring
  • Buffer Retainer
  • Buffer Retainer Spring
  • Trigger Guard
  • Trigger Guard Pin
  • A2 Pistol Grip
  • Pistol Grip Screw
  • Pistol Grip Lock Washer
  • Hammer
  • Hammer Spring
  • Hammer Pin
  • Trigger
  • Trigger Spring
  • Trigger Pin
  • Disconnector
  • Disconnector Spring
  • Bolt Catch
  • Bolt Catch Buffer
  • Bolt Catch Roll Pin
  • Bolt Catch Spring

Tools Needed to Build an AR 15 Lower Receiver

While it’s quite possible to Assemble an AR Lower Receiver with tools you have on hand, the experience can be frustrating with a less than desirable outcome. There are tools that absolutely make the task of assembling a mil spec lower much easier. Non mil spec lowers might lessen the need for special tools or require their own unique tools. Avoid buying import knock off tools. That will just create a whole new set of problems. In addition to tools it’s also advisable to have some grease on hand for lubricating pins and painters masking tape for protecting the lowers finish. Check out the Brownells AR Videos on the topic, they cover tools and  instruction. There are tool examples below. 

Mil Spec AR-15 Lower Parts Kit Examples

These are the kits discussed at the top of the page. I have bought a lot of LPK’s in my nearly 30 years of dealing with AR’s and while some of the parts seem to all come from the same factory I have seen quality differences of roll pins, detents and take-down pins. The higher quality roll pins are easier to install and fit better, the higher quality detents operate smoother. I have had take-down pins that are simply too tight.

Picture of a AR 15 Lower Parts Kit Mil Spec

Mil Spec AR-15 Lower Parts Kits

As stated above I have experienced quality differences among some lower parts kits. There was a time when Armalite was my go to brand but since the company changed hands I have not purchased a lower parts kit from them. Below is a list of a few that I recommend.

  • Palmetto State Armory – I don’t think any manufacturer has more LPK offerings than PSA.
  • Fulton Armory – I have bought many FA LPK’s over the years. I suspect these are the same as DPMS, don’t hold that against them. Fulton Armory is also a great source during times of shortage.
  • Aero Precision – As I write this I realize I pretty much stear shooters towards Aero Precision more than any other brand. Quality is consistent and they are priced well.
  • Stag Arms – comparable to the equivalent PSA and Aero Precision lower parts kits.

AR-15 Lower Parts Kit Less Trigger and Pistol Grip

If you are like me why pay for a pistol grip and trigger that is of no value. These AR 15 Lower Parts Kits omit the fire control group and pistol grip hardware.

Picture of a AR 15 Lower Parts Kit Minus FCG Pistol Grip

AR 15 Lower Parts Kit Minus FCG Pistol Grip

The AR 15 Lower Parts Kit Minus Fire Control Group and Pistol Grip is my prefered LPK. This allows me to save a few bucks and put it towards one of my prefered AR 15 Triggers and Pistol Grips. The same brands listed above would still be my preference in this category.

AR-15 Lower Parts Kit with Premium Trigger Upgrade

These AR 15 Lower Parts Kits feature an upgraded trigger and may or may not include the pistol grip. Armalite once dominated this area by including their respectable 2-stage trigger. There are better options available today.

AR-15 Lower Parts Kit Complete with Buttstock and Recoil Hardware

These AR-15 Lower Parts Kits are for the shooter who wants their LPK to include a buttstock, buffer tube, recoil spring, recoil buffer, castle nut and in some cases an upgraded pistol grip.