There have been problems with it since 3.13, but a broken calculator is still better than none. In my experience, most players are oblivious to the issue of what they carry nerfing their speed and stamina, and that is the real lesson to be learned. So just to repeat, a movement of 0.85 will keep you safe from most NPCs, and 0.9 or better avoids most players. You really need to be in the 0.9 region if you don't want to get shot up, and it's really hard to do that carrying a second full-sized weapon. Players often carry three weapons on their backs and go into combat with movements like 0.75 and it gets them shot up. So, here's the calculator you need albeit a bit broken.
Furthermore, you can learn a fantastic amount about any weapon you like with the tables at the bottom tabs. You can see for instance why the Gallant is the general favorite in Star Marine--low recoil, fast fire on burst mode, good damage, flat trajectory with no power drop to outrageous distance, light, large magazines leading to fewer reloads. It is not the best Time To Kill, but the weapons with shorter TTK have severe recoil that does not actually put the necessary burst on target. So if you go to the recoil tab you can see at a glance why the Karna is a poor choice. You can also see the Demeco is stronger than the Gallant in sustained fire, but weaker than the Gallant burst mode. LMGs are for laying down cover fire only (and that is better done with an S1 weapon from a vehicle with a shield, like the Ursa or a Grav bike.)
CIG has done really excellent work designing the stats in intricate detail.