This is the "hardcore" alternative. While not a standalone web app, the Gunsmith mechanic in is the most detailed virtual gun customization ever coded.
It features a massive arsenal—from AK-47s to RPGs—and includes realistic sound effects and unlimited virtual ammunition. pimp my gun alternative
The "Presets" menu in the game is perhaps the most detailed firearm simulator ever created. This is the "hardcore" alternative
It features thousands of licensed parts from actual manufacturers like Geissele, Magpul, and BCM. pimp my gun alternative