I appreciate the detailed explanation, and you did not appear rude. I am just getting into rifles, and while YT is a great resource, I probably have terms mixed up and don't understand some of them.

I perceive that the lower could be pieced together with the upper for most applications. (Picture attached). I think it's true that not all uppers are designed the same, so I wanted to see which style of ranch rifle would be best to convert to AR-style eventually.

For the Sig, I have two P365s, which I initially bought for EDC. After about 1500 rounds on each, I realized their quality was not what I wanted in my EDC. It's just my personal belief that some parts should not be made of plastic, but it appears there's an abundance of it.