Best AR-15 Mods & Upgrades

Posted by Modulus Arms on 1st Feb 2023

Best AR-15 Mods & Upgrades

The AR-15 is one of the most modular and enhanceable weapons of all time. Technological advances have allowed its performance to grow substantially and they’re still growing today. Whether it’s the latest weapon mounted light (WML), or the clearest optic, upgrading certain parts can have great performance benefits. At the end of the day, it’s the shooter and not the tool, but having better tools can help some.

AR 15 Upgrade List

Below we've compiled a complete list of AR15 parts that you can consider upgrading to take your rifle to the next level! 


Geissele Trigger

Triggers can be an exceptionally important part of the weapon, but it is also often misunderstood. Triggers should match the purpose of the weapon, not just be chosen based on the look or how light the trigger pull is. Generally speaking, while there are exceptions, cassette triggers in the AR-15 is usually not a good idea. They should also not be chosen based on the price alone. This is afterall, the thing that makes the gun go off. A poorly made trigger can be very dangerous, especially if the gun is dropped. No one ever plans to drop their gun, but no one ever plans to drop their phone either. Better safe than sorry.

There are a plethora of great brands and models out there to upgrade a firearm, but to keep it simple only two models; the Geissele SSA and G2S. The  G2S and related ALG triggers have become akin to an industry standard for budget, but solid and good triggers. There is a difference between these and the nicer triggers like the SSA, but it is only a noticeable upgrade to those with more time behind the gun.

The SSA was included because it is the only enhanced trigger that has passed NSW Crane testing, which includes a 5 foot drop onto a steel plate with the safety off; if it goes off, it fails. There are likely other high end trigger models that could pass the test, but Crane has only tested the SSA that we are aware of. More specifically, the full auto variant of the SSA, the SSF, passed the testing, but there is no difference between the engagements other than the lack of FA capability.

Charging Handle

Raptor Charging Handle

Charging handles are one of, if not the least consequential upgrade to the AR-15, however for competition and for suppressed shooters, it can make a noticeable difference. Competition shooters generally just want a large handle with which to pull the bolt back. This isn’t that it's necessary so much as they want to reduce any chance of failure to have the lowest time possible. For suppressed shooters, having a higher lip can really help keep some of the gas from escaping around the charging handle and therefore keeping the particulates out of their eyes. 


Optics are known for their complexity and breadth of options all over the market. Ranging from less than $100 into several thousands of dollars. What’s best? Well, like most things in life it depends, but you often get what you pay for. Purpose and budget will be deciding factors. Cheaper optics will often have worse glass clarity and worse parallax issues. The glass clarity is usually not too noticeable in the store, but it is very noticeable when the shooter needs visual information downrange through photonic barrier(s). 

Cheaper optics are made to look hyper clear in storefronts and can be deceptive about their real world performance. Parallax is the effect of reticle “moving” in the optic when the shooter’s head and eye moves to the side of the tube. While impossible to completely eliminate, this is much more pronounced in cheaper optics. If a shooter expects to be doing positional shooting or simply cannot afford to miss in case of competition or hunting, then spending more is good insurance. It is still on the shooter to be good enough to make the hit, but spending more will remove equipment variables hindering his/her chances of success.

Purpose will decide whether a red dot or magnified optic is the route a shooter should take. There are other options like reflex sights, but to keep it simpler for this long article we will treat it the same as red dots. These are for lighter wight weapons designed for shorter engagement distances of 300 meters and in. With production and fielding of these for decades now, the industry produces incredibly reliable and very long battery lasting optics. They are often much more durable than any iron sights also. Alternatively, fixed or low powered variable optic, LPVO, are an option. 

These will allow a shooter to have better positive identification, PID, of their target and just be able to aim better at distance. Whether it’s a retro build of the early GWOT with a Fixed 4X carry handle optic or it’s the latest and shiniest LPVO, having the ability to see further usually makes shooters more confident. Whether a it’s a red dot, LPVO or other form of advanced optic, it will outperform irons. For reasons other than budget, there is no reason to be using irons nowadays. 

Even then, there can be excellent red dot optics for those very budget minded like those from Holoson. As a final word or warning, do not use miniature red dots, MRDS, as primary sighting systems. While some want to do this because of how lightweight they are, MRDS have far more parallax than standard optics. Some even consider them too much liability as a primary sighting system.

Back-Up Sights

AR15 with back up canted sights

Presently an occasionally unpopular opinion: The back-up sighting system should be an optic. For all the reasons covered above, the back up should also be using more advanced technology than just precisely manufactured metal or polymer. The only exception for this is price. Iron sights are significantly cheaper and therefore do deserve a space for when builders are balling on a budget. Unless offset irons, which are available at a higher price, shooter’s will often have to remove their primary optic to use

Having a top mounted or angled optic is the preferable option. Understand that using a MRDS will result in parallax issues that are greater than standard RDS choices like the Aimpoint T2. Some find this acceptable to reduce the weight and the bulk of the back up optic. The chances of the primary optic going down is low, but it’s never zero. Others prefer to use a more solid optic like the T2.

For those on a budget though, it is difficult to argue with the Holosun options, like the 403C. Some want the reduced bulk and weight of an MRDS, especially given it’s unlikely to even be necessary. This does come at the cost of increased parallax however. A lot of discussion and debate continues on what angle is best, but it will depend on what clearances the weapon needs to be usable and the shooter's preference.


Magpul MOE Stock

Again, purpose and preference will play a larger factor in stock selection. We’ve provided some great and very widely liked examples below, but there are an enormous amount of options on the market. Some things to keep in mind: Durability, storage, cheek weld, weight and balance.

Magpul stocks are stringently drop and cold weather tested(low temperatures make polymer prone to breaking), so anything from them will be exceptionally durable. Some people like storage within their stock, but others don't. In the past it was common to store batteries, but shooter’s quickly learned that as they are used the remaining batteries bounce and make noise. Nowadays, cleaning kits, fire starting material and similar are what is often stored.

Moving on to more personal preferences with cheek welds, weight and balance, having storage generally means a wider cheek weld which will generally be more repeatable and comfortable; particularly in the prone. However, this all comes at the cost of extra weight and some bulk. Others prefer the lightest stock they can possibly find, however this often leads to weapons that are far too front heavy and therefore a poorly designed weapon. Those stocks are often made of less dense polymer and can be less durable. Unless the build is specifically a lightweight build, don’t let that be the deciding factor.


An AR-15 barrel

Barrels, barrels, barrels! A weapon’s barrel is the heart of the weapon. It will determine the purpose of the weapon and the majority of the build’s design. Before deciding anything else about a build, a builder should decide the purpose and then the barrel to meet that purpose. A builder will need to consider weight, accuracy, range and desired velocity at different ranges in order to decide what caliber, profile and other amenities they could consider. We’re going to leave caliber out of this article for now given that is an article in and of itself.

For barrel profiles, generally speaking, most shooters will want a gradually tapering profile to keep the weight balance better. This is the opposite of a mil-spec barrel, but given that most shooters are not attaching underbarrel grenade launchers(and neither is the U.S. Military, now often preferring to keep it detached) there is little point for this profile. A lot can be said about barrels and there’s an enormous amount to know that we simply can’t cover here.

Some generally well liked barrels are Rosco’s and Faxon’s. Those that want a hyper light build beyond even fluting, it doesn’t get lighter than Proof Research’s Carbon Fiber Barrels. It will mean giving up some accuracy over larger strings of fire though.

Muzzle Devices

An Aero Precision muzzle brake

Muzzle devices have a great effect on the weapons performance. From flash hiders, suppressor mounts, compensators or muzzle brakes; all with their pros and cons to them. Two important factors to consider are whether a build needs the capability to mount a suppressor, and if so, compatibility. Different suppressors use different mounts and a builder should reach out to their suppressor of choice. For more information on deciding on a suppressor and mount, look to Pew Science.

We have an Aero Precision muzzle brake for those looking for that we’re confident with. There’s also the FCD flashhider for those builders looking for a more balanced approach. A good balance between a muzzle brake and a flash hider is the SOLGW Nox. Whatever a builder’s preference for his/her next build, we at 80% want to be a part of it. 


Not a foregrip, but a handstop

Foregrips or Angled grips will be a lot of personal preference. It will be based on the shooter’s personal anthropometry, his/her hand size and the outer diameter of the handguard. This will take time and it is preferable to try before buying as much as possible. Going to training or competitions will allow shooters to connect with others to see what works for their purposes. If using tape switches or laser aiming devices, this will need to be tested even more stringently to make sure the shooter can always reach everything from a position they can still control recoil.

Polymer is almost always cheaper than metal based foregrips, but contrary to popular belief, they are rarely lighter when the size is the same. If they are, it is usually a negligible amount. This is because both use metal hardware for mounting and quality polymer is generally very dense within the firearms industry.

Some shooters prefer very slim, small grips and others prefer a bit more chunk. The trend over the last few decades has definitely been towards shorter and more angled. Some still use vertical grips, but they are often no more than around 3” in length. Compared to the older GWOT designs, this makes them far more maneuverable; simply less likely to get in the way, especially in buildings and vehicles.


A handguard, also commonly referred to as a rail

Handguards serve two main purposes and any handguard modification should have this in mind: Weapon manipulation and accessories. For weapon manipulation, there needs to be something to protect the shooter’s hand from the hot barrel. The greater the outer diameter, OD, the generally less comfortable it tends to be, but may be able to fit a suppressor underneath.

Fitting a suppressor underneath a handguard will make the handguard get hot much, much faster than otherwise though. The handguard also lets the shooter put vertical or angled foregrips to help the shooter better pull the weapon into their shoulder or brace against a barricade. With all of these, we want the handguard to have minimal effect on the barrel or have minimal bending if used with certain accessories.

For accessories, the handguard generally must have Mlok or Keymod. Mlok has overwhelmingly won that competition though as it is much stronger. Keymod’s only remaining benefit is that it is often slightly lighter. The handguard should generally go within 1” to 2” of the shoulder of the barrel or to the suppressor, whichever is closer to the receiver. Be sure to measure the barrel, muzzle device and more relevant devices when planning a build or upgrade. If a shooter is mounting a laser aiming device, such as a MAWL or PEQ-15, then the rigidity and repeatability of the handguard will be a critical factor.

Currently, nothing on the market beats the Hodge Defense Spine Lok, more commonly known as the S-Lok, with respect to maintaining the zero of a laser aiming device. But, without a laser aiming device, there is substantial room to reduce the weight of the handguard. Going with Carbon fiber or 2099 or other high grade aluminum alloy can shave significant weight off the rifle, while still letting the shooter mount their WML and switches.

Lower Parts Kit

If the goal is a standard Colt style build could be the answer for the builder wanting to keep it simple. If reading on is too much, builders can go with the below kit. While it might leave some performance on the table, it does provide a lot of value for the cost. This can be the easy button for those that need something simpler or more straightforward.

Anti-Rotational Pins

Anti-walk or 'rotational' pins.

An often seen “upgrade” to the Ar-15 is anti-rotation pins. They're hard to get away from if you are buying drop-in trigger upgrades since they will typically come with the anti-walking pins. You might want to think twice on whether you should or shouldn't buy them. Sometimes they can actually damage the weapon over time. What happens is that because the pins cannot rotate, they will grind out the pinholes in the lower receiver making them larger.

This is why oversized pins are sometimes sold. Whenever considering deviating from Eugene Stoner’s original design, there must be great care to not be making the weapon worse. The original design calls for the pins to float and rotate just slightly. If your pins in the lower receiver are walking out there are other solutions to this problem as well.

See here for more details on why anti rotating pins are not liked by some. 


Magpul K2+ grip, great for AR pistol builds

Grips have a lot to do with a shooter’s hand size and the purpose of the weapon. The standard USGI is very aggressively angled compared to what has been the industry's direction the last few decades. The more vertical grip upgrade will place the wrist in a more comfortable position that is also stronger. Ensure the length of pull is correct for the hand size as well. Trying multiple grips at the local gun store will help decide which best fits the shooter’s hand. For precision, completely vertical, specialty grips are often used.

Ambidextrous Safety Selectors

Ambi safety lever
Generally, there are two schools of thought to ambi safeties. Some believe they should not be used. Just have it on the side of the weapon hand’s thumb. Leaving it to one side is safer than having it get manipulated by the environment and it will not interfere with the shooting hand while firing. There is real merit to this opinion and it is born from experience.

But some others disagree and believe it’s acceptable and useful. There are some great options out there, and also a lot of terrible ones. Remember to exercise good judgment when deciding what safety to use as it can be a matter of life and death. The Radian Arms Talon and the FCD ambi safeties are typically the most well liked and trustworthy brands.

Extended Bolt Catch / Release

The Extended Bolt Catch / Release is a great modification to the standard AR-15. Engaging the bolt catch manually can be troublesome to very difficult for some shooters, particularly the elderly, younger and less abled in society. Having a larger catch makes this much easier. Adding mass to the bolt catch will affect the function and timing of it working with the weapon’s operating system.

Be sure to use the spring that came with the bolt catch. Using a low quality bolt catch can lead to the weapon failing to lock open when the magazine runs out or cause the bolt to close when it shouldn’t. Using quality parts is important for any weapon. Some common aftermarket upgrades are the Geissele and FCD options listed below. The other option is to use a proprietary lower. This is usually done to make it ambidextrous. Most people find it very dependent on personal preference, so it is best to try it before purchasing if possible.

Extended Magazine Release

Magpul Extended Magazine Release

Magazine releases are often a uniquely personal touch. Two main methods for differentiating from the standard pattern: One is the standard lower with more advanced parts and the other is for a proprietary lower; usually to make it ambidextrous. Ensure that any aftermarket parts work with the chosen lower. Proprietary parts sometimes mean it won’t work with other parts.For ambi lowers, personal taste is a strong factor. There are some who only want ambi Bolt catch, some who just want an ambi bolt release without the catch functionality and others want every single part to be ambidextrous.

There has been a trend towards only having the bolt release, but it varies. It is also heavily affected by whether the shooter is shooting right or left handed. This should be determined by their eye dominance, but that is an article for another day. Only by trying different lowers out will a builder be able to know what works for them. Going to training classes or competitions can be a great way to meet people who have these products for a builder to try.

Bolt Carrier Groups

Bolt Carrier Group

Messing with the BCG can increase the reliability or wildly influence the felt recoil. It’s the soul of the rifle and needs to be understood. At approximately 11 ounces in the original design, deviating from this should only be done by experienced builders. While there is substantial desire to make the lightest AR-15 possible and the BCG is a big part of that, Jim Sullivan and similar have viewed this as confounding. That doesn’t make it wrong. To them, reliability and repeatability was the name of the game; later on it was recoil averaging technology. For competition shooters, not long range, lighter BCGs have been extensively experimented with since then and have been made much more reliable. They are not as reliable as heavier set ups, but they do work better than before. Researching how Vseven, 2A Armament and JP Industries could be very helpful in navigating the sometimes daunting world of lightweight builds.

On the extreme reliability (and price) front, it’s a somewhat common upgrade to have a KAC Sandcutter Bolt Carrier or similar high quality part with the bolt of their choice. The bolt carrier can be used with most bolts on the market. Some really like KAC’s rounded lug design on the bolt for reduced stress on the lugs, a common point of failure under extreme use, but these are limited to be used in KAC barrels. Granted, those barrels are excellent and will serve anyone well when precision during heavy firing strings is the priority.

Keep Your AR Upgraded with Modulus Arms

Wow, that was a lot to cover on how to modify your AR-15. Upgrading a weapon can be an involved process when done right, especially at first when shooter’s are hearing it all for the first time and not knowing up from down. It’s important to stay relatively up to date with the latest capabilities and Modulus Arms hopes that we can be that solution for you. Whether you should build or buy, and don’t forget to lubricate that AR-15.