AR 15 Upgrades: Parts to Replace

AR-15s have quite a fan base and for good reason. They are versatile and incredibly customizable. Aftermarket part options are available for just about everything—okay, for everything—making AR 15 upgrades possible on many levels. Want to replace your trigger? There are drop-in or component kits for that. Interested in a specific brand and style of takedown pin? That exists, too. If you’re thinking about AR-15 upgrades, though, you might be wondering where to begin. You know your rifle needs a little something extra, but what? Don’t worry, we’re here to help.

AR 15 upgrades
Factory AR-15? Did you know you can do AR-15 upgrades to your heart’s content? (Photo credit: Kat Stevens)

AR-15 Upgrades to Consider (and Why)

If you’re truly unsure where to start with your AR 15 upgrades (not accessories like scopes and red dot sights), there are a few specific gun parts to focus on.

If you’re not clear on the basic parts of the AR-15, they can be broken down briefly as follows (this is not a complete parts list, it’s simply a rough breakdown of major components):

Upper Receiver

  • Barrel
  • Handguard
  • Upper receiver
  • Bolt Carrier Group
  • Charging Handle

Lower Receiver

  • Lower receiver
  • Trigger
  • Safety selector
  • Grip
  • Buffer tube
  • Stock

In its entirety, an AR-15 actually has an average of approximately 100 parts. That’s if you count every detent pin, spring, and castle nut. You can see why getting into each and every component takes time. From a general standpoint, it’s fine to focus on specific important parts when you’re looking for aftermarket AR 15 upgrades. What parts are those? We’re glad you asked.

Do I Need a New Bolt Carrier Group (BCG)?

This Noveske BCG is a great example of a high-quality component. (Photo credit: Noveske)

Your AR-15’s bolt carrier group is the heart of the rifle. Without a well-made, properly-functioning BCG, your gun won’t fire or cycle. Within the bolt carrier group are the following smaller parts:

  • Bolt carrier
  • Carrier/gas key
  • Firing pin retaining pin
  • Bolt cam pin
  • Firing pin
  • Bolt (with extractor and extractor spring)
  • Gas rings

The simplest way to handle AR 15 upgrades where the bolt carrier group is concerned is by replacing the entire assembly. It is possible to buy specific parts of the BCG but it’s typically a better idea to get a totally new one. With the right BCG, your AR-15 will cycle reliably, function dirty, and fire reliably. If it’s a lower quality BCG you could be experiencing failures to extract, failures to feed, and numerous other problems. The BCG is a great part to replace.

When replacing a BCG, check the following features:

  • Material made from
  • Finish, which affects cycling and longevity
  • Bolt face, the size must match what your AR-15 is chambered in
  • Solid or skeletonized based on personal preference and gas system
  • MPI and HPT tested

Consider BCGs with finishes like Diamond Like Coating (DLC) and nitride for superior cycling and resistance to wear. Some AR-15 owners also like nickel boron as an AR-15 upgrade option. The most common finish tends to be parkerized because it’s more affordable, but it also has some drawbacks for serious shooters. As for material, most BCGs are made from steel, so do your research regarding the type and grade of steel they’re made with. Titanium is also a possibility for AR-15 upgrades to your BCG, but it does spike the price.

Should I Replace My Trigger?

Timney Triggers Calvin Elite AR-15 trigger
The Timney Triggers Calvin Elite AR-15 trigger is an exceptionally well-designed trigger and comes with an assortment of interchangeable trigger shoes. (Photo credit: Timney Triggers)

In short, yes. Odds are the trigger your AR-15 shipped from the factory with is less than ideal. That doesn’t mean it’s a terrible trigger, only that there are probably better designs on the market. Most AR-15 rifles are sold with MIL-SPEC triggers, a phrase that makes some gun owners happy but that really isn’t exactly a compliment. Basically, it means it’s a very basic trigger that gets the job done with no bells and whistles, but it can also mean a gritty trigger that stacks or otherwise hinders your ability to shoot accurately.

There are two general options for AR-15 upgrades to your trigger: the drop-in cassette style and a parts kit that must be assembled. One is clearly simpler than the other but both have benefits. When you’re choosing an aftermarket trigger for your AR-15, consider:

  • Trigger pull weight
  • Adjustability
  • Trigger reach
  • Trigger blade or shoe style
  • Interchangeable shoes, if it’s an option
  • Color
  • Texturing on trigger blade or shoe face

Generally, replacing an AR-15 trigger means the shooter is trying to get a lighter, smoother pull. Having a quality trigger means greater accuracy and precision; there’s a significant difference between trying to get precise shots with a MIL-SPEC factory trigger and a crisp, clean aftermarket trigger. Companies that make fantastic aftermarket triggers for AR-15 upgrades include Timney Triggers, Elftmann Tactical, CMC Triggers, Geissele, and TriggerTech. Swapping triggers is a relatively simple process, so it’s a minor investment of time for a major payoff in results.

Should I Replace My AR-15 Stock?

Magpul CTR Carbine Stoc
The Magpul CTR Carbine Stock is a good example of a nice adjustable stock with a great angle on its upper surface for a solid cheek weld. (Photo credit: Magpul Industries)

It can be easy to discount the importance of what stock is on your AR-15. You might have a design that works well for your purposes, or you might discover changing the stock makes all the difference. If your AR-15 came with a fixed stock or one that has extremely limited adjustability it might benefit you to consider it as one of your AR 15 upgrades. What features can be great to have on an AR-15 stock?

  • Adjustable length of pull (telescoping)
  • Cheek risers
  • Cant adjustable
  • Height adjustable
  • Removable spacers (inserts)
  • Angle and overall shape (too narrow or bulky affect cheek weld)
  • Lighter weight (or heavier)

Everyone has a different body type. Your length of pull and how you get a good cheek weld won’t be identical to what your best friend needs. If your existing AR-15 stock works for you, fantastic; if your AR-15 upgrades need to include getting rid of an ill-fitting stock, do it. There are some situations where a fixed stock works but those tend to be the exception rather than the rule because they so severely limit good fit. Another pro of an aftermarket stock is that it makes it easier for other shooters to run your gun well. With just a few clicks, the gun will suddenly fit them better.

Stock fit matters. If it’s too short, too long, or at an awkward angle, it hinders accuracy (not to mention comfort). For your initial AR-15 upgrades consider getting rid of your factory stock.

Should I Build an AR-15?

Aero Precision AR 15 parts
Thinking about building an AR-15? Aero Precision is a popular manufacturer of parts. (Photo credit: Aero Precision)

Building AR-15 rifles isn’t for everyone but if you’re willing to try it, it can be fun. As we mentioned before there are around 100 parts in an AR-15. If you’re going to build an AR-15 it’s a good idea to learn about the various parts before buying them. It’s better to take longer to get your AR-15 built than to do it cheap and fast. Be warned, once you build an AR-15, you’ll want to keep building them. And just think, if you build an AR-15, those AR 15 upgrades you would’ve made to a factory rifle will be in place from the start.

The options are endless. Focusing on specific parts before getting into the smaller components is a good way to get the greatest possible results right away. What are some of your favorite AR-15 upgrades? Tell us the details in the comments section.

Kat Ainsworth Stevens is a long-time outdoor writer, official OGC (Original Gun Cognoscenti), and author of Handgun Hunting: a Comprehensive Guide to Choosing and Using the Right Firearms for Big and Small Game. Der Teufel Katze has written for a number of industry publications (print and online) and edited some of the others, so chances are you've seen or read her work before, somewhere. A woman of eclectic background and habits, Kat has been carrying concealed for over two decades, used to be a farrier, and worked for a long time in emergency veterinary medicine. She prefers big bores, enjoys K9 Search & Rescue, and has a Master's Degree in Pitiless Snarkastic Delivery.


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