Tolerance Stacking and After-Market Parts

With an influx of new firearms owners, we're seeing members wanting to take their new firearms and begin installing upgrades. Before we begin adding new parts and equipment onto a new gun, we should pause and consider our use case for the firearm: Is this an every day carry (EDC) handgun that has to have 100% reliability? Is this a competition firearm being run with a specific load and with the idea that every bit of performance is going to be squeezed out of the gun even if it compromises reliability? Or is this a firearm that only sees range use and isn't being relied upon for home defense?

There is a phenomenon known as tolerance stacking that arises when we start introducing non-OEM (Original Equipment Manufacturer) parts into firearms. Every component in a firearm is manufactured to a specific dimension which is designed to work with other parts that they interface with. For example, in an AR-15, the bolt carrier group (BCG) must be within a certain tolerance range in order to interface efficiently with the rest of the firearm. If a new BCG isn't within the tolerances designed by the manufacturer of the upper receiver, it may experience malfunctions, be inefficient, or wear out prematurely.

When we become new firearms owners, there's often a burning desire to to modify a new-to-us gun in all kinds of ways but these modifications can occasionally cause problems. Quality Control in firearms manufacturing is always done with the manufacturer's parts and tolerances in mind; when we start adding or replacing parts, we are operating outside of the intended tolerances set by the manufacturer.

For example, adding an upgraded drop-in trigger to a handgun can provide a lighter pull and a crisper break if the new trigger can operate within the firearm manufacturer's tolerances. The new trigger bar might also might not have enough clearance and could prevent the pistol from functioning when needed. Replacing the A2 flash hider on an AR-15 with a compensator will reduce felt recoil and negate muzzle rise while making double alphas (two repeat “A” zone hits on an IPSC target) easier to acquire in a competition. However, that same muzzle brake will make the rifle incredibly unpleasant for others on the range and dramatically increases the potential for permanent hearing damage if used for self-defense without ear protection.

Recently, we had this discussion in the Southeastern Region's communications platform. Sky, an organizer for the North Georgia chapter of the SRA, shared these thoughts:

“There is no such thing as a 'do everything gun', or at least no 'do everything well gun.' A lightweight gun is going to be better for hoofing a rifle around on recon or a Walking Dead style apocalypse. A heavy gun is going to be better for precision and recoil management. A shorter gun is going to be better for maneuvering small spaces. A longer barrel is going to be better for shooting further (more velocity.) A red dot is going to be better for fast shooting with less precision, while a scope will be better for further and more precise shooting.”

The new gun owner would do well to not only cautiously vet firearms manufacturers but also the manufacturers of after-market parts. There are countless tales of after-market mounts with dubious metallurgy purchased from Amazon sending a new optic bouncing off of concrete or failing to maintain zero after a range trip. Firearms manufacturers will also commonly void the warranty on a firearm if after-market parts are found as part of a claim.

This is also why it is critical for new firearms owners and leftists interested in self-defense to have some form of community to further their own education. The gun store employee working on commission, the YouTube content creator shilling the latest and greatest piece of gear, and the internet stranger on Reddit all have one thing in common: they are fundamentally not accountable to you and will be unlikely to help if turn your new rifle into a boat oar trying to install an ill-advised after-market modification.

We keep us safe from Wish.com AR-15 mods and bad subreddit firearms advice.