If I was going to spend $3,000 on a factory AR 15 would buy the MGI Hydra that comes in a nice case and can swap it to four different calibers with barrel lengths of choice basically without any tools.
https://www.mgi-military.com/store/i...e=&category=21
If going that far in would buy the five caliber kit that can choose from many choices but their most popular kit comes with any five of the below listed calibers that all snap together on a single registered receiver. Actually can buy all listed and use on same receiver and technically only own a single rifle.
22 Long Rile
5.56 x 45
.300 Blackout
5.45 x 39 (AK-74)
7.62 x 39 (AK-47)
6.5 Grendel
6.8 SPC
9mm SMG-9C (Colt-Style Mags)
.50 Beowulf
https://www.mgi-military.com/store/i...e=&category=21