A loose and constantly out of adjustment hopup dial is one of the most common and annoying problems with almost every brand of M4, M16, M733 or AR-series airsoft rifle.

If you have ever owned or used a M4A1 or similar AR-series AEG, you know how annoying it can be to have your hopup constantly losing its adjustment. I’ve tried dozens of field “repairs” including chewing gum, stuffing material under the dust cover and electrical tape – most of which only create a temporary fix. What I’ve done with my own M4 style guns:

The lock washer (or split washer) fix

My favorite fix is to find a small lock washer that will apply extra pressure to the hopup dial/wheel. I’ve used several types of washers and found that split washers do a great job of adding extra tension to the dial, allowing for a much more precise adjustment – that stays in place!

Replace it with a new unit

There are quite a few versions of replacement hopup units out there, so I can’t make a single recommendation for every version/model of gun. In some cases a replacement may be the right solution, but I would start with the washer fix unless you’re having other problems with your hopup.

Replacement hopup unit from Airsoft Extreme.

Metal hopup from Airsoft GI.

If you have some ideas or ridiculous things you’ve done to fix your M4/M16 hopup, leave a comment, I’d like to hear about it. -6mm

Learn how to rewire your M4A1 from the fore grip to a rear stock. This video includes a complete removal of the trigger, electrical components, selector plate and cutoff lever in a version 2 mechbox.

Now that you’ve taken the M733 apart, this video will show you how to put it back together.

The M4 and M16 are very similar to the M733 – so you can use this guide for most other models. You will see differences with the M16VN and other manufacturers like ICS, Classic Army, JG and so on.

This video demonstrates the body breakdown and disassembly for a Tokyo Marui M733. This video could also be used as a generic guide for most M4, M16 and other Armalite models.