You need to use a very mild abrasive that will polish but not scratch the surface. Most toothpastes fill that niche. Take a small amount and put it on a damp cloth and try rubbing out a small section at a time. You can also buy some "rouge" buffing compound and do the same thing. But most people have toothpaste around and it seems to work pretty well.

We used to use it years ago when convertible tops had plastic windows in the back. They would yellow and scratch. The watered down toothpaste worked well on clearing them up.

They also work on hazy plastic headlamp covers. But by hand any one of these is a time-consuming project. But still, I would tackle the gun by hand rather than risk flinging the weapon across the room with a buffer.

Years ago I used to call on a company named "Farberware". They made stainless steel pots and pans. They were hand polished on big buffing wheels. The company did not heat the building so the buffers all wore winter coats in the cold weather. I warned the production manager that this was a high risk situation, and that the buffers should be working in short sleeves.

A few weeks later a buffer got his coat sleeve caught by the buffing wheel and it tore his entire arm off at the shoulder. Not cut off, torn off. So buffing, even though it has no sharp edges, is not a operation to take casually.