Interchangeability of the AR-15
I've been wanting to build an AR-15 for a while. I want to get a lower receiver that will allow me to change calibers simply by switching the upper receiver. As I understand it, this is one of the main benefits of at AR platform.
The calibers I want to be able to shoot with my lower include 5.56NATO/.223REM, .308WIN/7.62NATO, 30-06, and maybe even .338 Lapua.
Nw, I realize there's an AR for each of those calibers, but here's what I think my issue is going to be: Because of the difference in cartridge size between these calibers, I'm concerned that the magazine well in whatever lower I get would never be able to hand ALL of these calibers. So, is there even a lower receiver in existence that would allow me fire all my desired calibers (understanding that I would have to buy separate upper receivers for each caliber)? Or is this just a wild pipe-dream of an AR-15 noob?
Thanks in advance for the advice!