That’s why I chose the M4e1. I bought the upper but might be in over my head assembling the barrel to the upperA-P did a nice job designing your lower.
With that particular lower, you escape what I call the two "Man-Boy" separators in an AR build.
1) The trigger guard roll pin.
Many sob stories of broken ears.
Yours is integral.
2) Bolt Catch Roll Pin
This is another tricky pin to drive.
There is actually a How-To video on the Web where the guy mashes (folds over) the end of the pin and calls it good.
Others show the Plier Method and some scar up their lower doing that.
Yours is threaded, so no roll pin to drive.