Is the 35 caliber not such a popular round in the pcp game?

So I have read all of this and now I’m worried that I spent way too much money on a gun I don’t need. I’m talking about my new SP M60B in .35/357 or 9mm. If I understand this correctly I can put actual firearm bullets through this thing. Advice is needed before I even air this thing u, or should I just sell it and buy a good.30 from a more accessory friendly brand. I can’t find much in the way of information or product for this gun. Got off eBay for $500 and thought it would be my entry into big bore rifles. I like the idea of learning how to cast my own bullets. I could build a decent mold and get some quality lead and do that I suppose. Would tumbling them with a fine medium help at all and. I don’t know how to resize a bullet. But the tumbling idea seems viable. Has anyone ever tried that approach to ensuring the projectile is clean and free of crap. I was thinking of trying it with some of the.25 slugs I get. I have been buying what I assume to be “homemade“ slugs off eBay. They come marred or looking odd sometimes and I wonder about that. I am pretty new to PCP so dont get offended by my ignorance.
By the way. I’m well rounded with the gunpowder variety of firearms. Just not AirPower ones. But I admit this is really fun. I acquired about 12 sub $700 PCP’s. Including two mods, an armada, origin, gauntlet 2, notos, two barra’s, both types of jets, an arrow, a virtus, a vectis (favor), and even a stoeger. So basically every entry level gun other than a Diana stormrider or beeman chieftain. Yes impulse control is a problem. Jajaja. I also just ordered the tequila gun in .30, looks like a good gun and the designer is very cool and very knowledgeable about airg design IMO. he communicates directly with me and has been awesome to text with. More inevators should get into this and further propagate the airgun game. In a catastrophic situation air is free and gunpowder is not. Still needing advice on m60b situatio? please and thank you