Looks like a hot mess. Either you have a lot of hard work ahead of you to manually remove all that stuff, or you need to just break down and get some help. If it was me, I would completely disassemble it and work on the optics, synthetics, and metal separately. First the metal. If you can't strip the paint, then find someone with blasting capability, preferably something like 180 grit alum oxide at about 60-80 psi. On the synthetics, again if it strips, fine, if not blast. On the optics, This where I'd take my time and do it by hand. I'd just remove enough to get it down to base finish and/or ready for a re-coating. Completely mask and seal the optics. Use the chemicals sparingly. Lots of scotchbrite here. Then use any coating with a non-thermal set.
This is the down-side to weapons coating. When you get this kind of build-up to remove, it's a major re-furb. I don't screw with it; I break it all down and blast it. The only refurb I do on optics is to scotchbrite the existing coating to smooth or even it out, and then recoat.
Short answer: There is no easy way to remove this kind of build up, on metal, polymer, and optics.