These guns weren't designed with cleanup as a major consideration. Fouling, whether carbon, powder, or both becomes quite prevalent throughout the receiver area after firing only a few rounds. If there is a difference in the degree of fouling between commercial ammo or handloads (even using a variety of powders), it's minimal.

A bolt radius scraper (that may be what you are referring to) is inexpensive and quite useful. I use one from Brownells. Also, a chamber brush is essential. Most of us want 100% reliability; a clean chamber won't guarantee that but it sure helps.

I don't know how many rounds can be fired before cleaning becomes necessary. I've never fired more than maybe 250 rounds without cleaning. I soak the bolt carrier assembly parts in kerosene for a short time to loosen up fouling.

There's more to cleaning and others will have additional and perhaps better suggestions, but these work well for me. Get good cleaning equipment. From my experience, Otis products don't qualify.