Actually, the open top receivers of the M1 and M14 aren't all that:
http://www.thefirearmblog.com/blog/2015/02/20/the-m1-garand-dust-mud-1950/
Instead of resorting to snarky egotism, lets use some common sense. The open receiver of the M1 series was prone to severe jamming from dust and muck.
The FNFAL wasn't. That's because it has a shrouded action.
The AR10 had a shrouded action, too.
Try it yourself and report back - set up a trial and see which will repel dirt better. In the day, and somewhat unscientifically, I did the same with some buddies who were trying to convince me that the HK91 was good to go. We went to the local abandoned mine pits where millions of cubic yards of crushed smelter gravel remained, opened the chamber, poured in a handful, and
Closed the bolt and fired a full mag. No stoppages.
I'll take a nice loose rattly bolt and clacking upper to lower fit every day over a tightly fitted work of art.
What do you think Stoner was trying to improve on? The known defect in the M1/M14 open receiver design.
They weren't all that and still aren't.