All About Trigger Packs

by Steve Coffman, last updated on

It can be difficult to understand the functionality and legality of trigger packs, regardless of if you are new to guns or a trained shooter.

In simple words, a trigger pack is a mechanism that enables you to convert a given gun into a semi-automatic or automatic weapon. There are many different types of packs, and different packs fit different guns.

There’s also a huge community that modifies their trigger packs to fit other guns in their collection or work better with their weapon of choice. But trigger pack modification is a topic for another day.

In this post, I will tell you all about trigger packs.

All About Trigger Packs


A trigger group has several distinct parts, but the three parts that you need to know about are the housing, the trigger pack, and the sear(s).

The housing is the shell that contains the trigger pack inside of it. It comprises a handle (or grip) that enables you to use the trigger group.

The trigger pack may include one or many sears. The sear(s) are what convert a weapon from a single-fire to a semi- or fully-automatic firearm.

In a semi-automatic trigger group, the sear engages every time you pull the trigger, causing a single round to fire. 

On the other hand, in fully automatic or selective fire trigger groups, the sear is only engaged one time, and the weapon fires until you let go of the trigger (or you run out of ammunition).


There are four types of transferable fully-automatic trigger packs:

  • Registered receivers with double pushpins 
  • Registered receivers with unregistered conversion devices 
  • Transferable sears 
  • Registered trigger frames 

While getting your hands on any of these will do the trick, many in the gun community hold the opinion that the registered receivers with unregistered conversion devices aren’t worth the investment. 

These aren’t as versatile as the other options, so many in the community avoid getting them altogether.


If you’ve been active on forums or are a member of your local gun range, you probably will be aware that fully-automatic rifles were banned back in 1986 when the Firearms Owners’ Protection Act was passed.

Therefore, automatics manufactured after May of 1986 are illegal. However, there is a workaround. You can get your hands on an auto-sear and take approval from the ATF.

Getting a trigger pack is a lot easier, though. While technically it doesn’t make your gun fully automatic, it does simulate the effect by firing both the pull and release strokes of the trigger.

The legality of trigger groups varies widely from state to state, and sometimes, cities have a different set of laws than the state as well.

However, with the HK platform, you do have two options for getting your hands on a legal trigger group: transferable full-autos, and registered receivers.

There is another option – the registered trigger box. However, these are rare, and finding one is next to impossible.

Buying Advice

Unlike the AR platform, the HK 90 series isn’t very easy to modify because of how the barrel is pressed into a trunnion. 

So, if you’re looking for something that gives you a lot more flexibility and allows you to switch between hosts, getting a registered sear pack is the right way to go. 

The sear is nothing but a small H-shaped piece of steel. However, it’s fortified, allowing it to smoothly interface with the F/A trip lever that comes in the pack.

The sear takes a secondary position on the hammer, allowing it to control the timing and ensure that the bolt is in a full battery before the shot is fired.

It’s important to note that a registered sear is considered a machine gun by the ATF, leading it to cost in excess of $20,000. 

Dismissing a trigger pack as a tiny piece of metal that costs a lot of money is not the right thing to do. You must understand that you’re not paying for the piece itself, but for the paperwork owning one entails.

A registered sear fits directly into the primary sear-return spring axle in the pack. So, in order to avoid creating a new machine gun entirely, the trigger box must be modified. Modification is also required so the sear can fit the existing shelved upper receivers.

Registered sears tend to be longer than auto-sears since they use a different axle to work with the secondary sear of the hammer.

The internal change in geometry affects the hammer’s position, typically resulting in a result in the fire rate.

Getting a registered sear is also recommended since it works with all of the HK-90 series, provided that you have an F/A bolt carrier installed.

It’s vital to keep in mind that some minor changes may be necessary to make it work.

You could also get your hands on a burst trigger pack since it is possible to use a registered sear in them. However, burst trigger packs tend to be a lot more complicated than SEF versions.

There are companies out there that can install it for you, but if you don’t like the result, it’ll be hard to get your money back from them. 

Even if you pay for insurance for your weapon, for the insurance company, the gun is lost, and they won’t pay your insurance claim – especially considering that your gun will be classified as a “machine gun.”

Getting your hands on belt-feds is not a bad idea, either. However, the pack will need to be modified to work with the belt-fed ejector. Also, you will need to use a different belt-fed re-timed hammer.

So, keeping all of these considerations in mind, it is recommended that you get your hands on a registered sear. If you haven’t modified a weapon before, I suggest that you visit your local gunsmith for help. 

Having a functioning weapon is better than one that’s broken, and if you’re new, you should put your faith in the professionals to modify your weapon for you.