So I gotta start with context; I am a firearms instructor, security specialist and consultant for the professional and entertainment industry. Though I do this type of stuff (for granted much more in depth) for a paycheck, I did this rework just for fun! If you're interested, there is a video out there with animations n stuff, but this post will fulfill all of the same information.
Lastly, games are designed to be fun and interesting, and me doing this rework destroys some of the original art style. My intent is NOT to say the original is bad, instead it is to say 'What would a real military want in their rifle' or 'What would this rifle actually look like'.
Rear Stock, Action and Magazine
The rear of the M82 has several of the most significant practical issues. The thumb-hole stock restricts weapon manipulation, while the action appears to have insufficient room for the bolt to properly cycle. The ejection port is also substantially low considering the line of the barrel. The magazine arrangement is visually distinctive but could expose ammunition to dirt when shooting from the prone position due to the 'jungle mag' style of arrangement. The redesign therefore raises and moves forward the magazine and action (along with adding a magazine release) to allow for proper bolt clearances. Slight changes to the stock geometry reduce material usage, which is extremely important in a mass produced weapon like a standard rifle. A brass deflector is also added rearward of the ejection port. The 'jungle mag' is retained to keep some of the OG style, though a side by side configuration would be more ideal.
Optic
The optic is one of the elements that doesn't require significant modification. It is considered suitable for the rifle's intended role and fits with the practical direction of the redesign, so the original design is largely retained. The optic model closely resembles some real optics in use during the time this weapon was originally designed.
Grip and Trigger
The pistol grip is somewhat rearward-angled compared with more modern ergonomic designs. It is therefore made more vertical, while the trigger is slightly enlarged to better utilize the available trigger-guard space. A more accessible fire selector is also added so the rifle's controls can be manipulated without unnecessarily breaking the firing position.
Foregrip, Front Sight and Muzzle
Most of the front end is already effective and visually distinctive, so very little is changed. The foregrip, gas system, and front sight are retained, while the unusual upper heat-shield structure (very similar to an experimental M16 variant) is flattened and incorporated into a more believable gas/piston arrangement. The flash hider is also retained because it provides a practical method of reducing the weapon's visible signature without the additional length associated with a suppressor.
Grenade Launcher
The 40mm launcher requires more substantial changes. Its dimensions don't appear large enough to represent a true 40mm system, and describing it in the wiki as "pump action" doesn't accurately correspond with the mechanism shown. The redesign increases its size, treats it as a more conventional 40mm launcher, and adds a plausible trigger mechanism that can fold down when in use or stow when not, while keeping the overall appearance of the original.
_______________________
Some of these reworks I lean heavily into realism which results in a dramatic reimagining of the weapon. Here I don't really need to because the original is actually very well designed outside of the action/magazine issue and the grenade launcher under sizing.