How ARs multiply:
First you buy a complete AR, then you put in a better trigger, then find a new stock and grip you like better, then realize most factory built rifles are overgassed so you buy a new spring, H2 buffer, and M16 carrier. Then you want a new upper for longer range, then you realize if you just get another lower and few small parts you can assemble another whole rifle, but of course, this one has the grip, stock, and trigger you didn't like before, so you replace those too ...
It doesn't stop.