@Dawn, I bought stripped lowers and put mine together like a Johnny Cash Cadillac, one piece at a time.
I’ve mentioned my rifles before but will recap again. In CA you can run featureless or fixed mag and keep the pistol grips, adjustable stocks, muzzle tips of any type and not have to register as an assault weapon. I use the juggernaut tactical hellfighter maglock kits and live them.
My favorite is a juggernaut tactical JT15. It’s a billet lower with ambidextrous bolt catch release levers, and a threaded bolt catch lever pin. Magpul grips and MFT minimalist stock. Chambered in .223 Wilde 16’ barrel with 1 in 7 twist.
I also have an anderson am15 forged which works just fine nothing fancy in 5.56 16” barrel 1 in 7 twist. Daniel Defense furniture and iron sights which are my favorites, they feel ergonomically better than magpul, fitment has a tight tolerance and the sights are great fixed sights.
Last is an aero precision M4E1 forged which is nice, I like the threaded bolt catch pin and fit and finish is nice as well. I chambered it in .300 blackout 16” 1 in 8 twist with a pistol length gas system, I found a magpul matrix diversified MOE furniture kit in wild fire camp.
My friends have Smith and Wesson MP15s and when talking with folks at my FFLs a few have mentioned the Ruger ar556 that @Orpackrat mentioned.
Putting them together is fun and you can spread the cost out with all the nice options you want, barrels, triggers, furniture, sights/optics.