In this case, I'm not sure how much the WN can help you. The Manga really isn't an adaptation of the web novel. I'm assuming it's an adaptation of the LN instead, and the writer met a good editor when he made the jump from wn to ln. The plot has undergone an overhaul from the WN, becoming less...
Looks looks like a sfw version. You can see it's nsfw in related
SFW (Suggestive by mangadex.org tagging)
https://mangadex.org/title/6a528a50-491b-4a88-81ac-50d92c182089/
NSFW
https://mangadex.org/title/b3be86e4-b976-4f6c-bca5-5ef86d456a78/
For real world purposes, yes. They're both small spheres. If you want to get technical. The BB in BB pellets is a shot size. BB pellets are supposed to be .18 inches in the US, but if you go to Academy, you'll usually see .177 BBs. The balls of a ball bearing are what ever size they need to be...