AR comparability question

[Halfey]

I'm considering building an AR and I was wondering if I build one in 5.56 can I swap out the upper with a 7.62 NATO or 22lr upper (or any cal for that matter)?

The reason is that at this time I only want one AR but I don't want to be restricted to just 5.56.

I have heard that the AR platform is completely moduler and all the intercaliber parts will interchange with one another. Is this true?

Sorry for the annoying question. if any of you AR guys could help out this handgun guy that would be great!

Thanks!

[MrPlink]

7.62nato won't work. Its too big for the lower, it would require an "ar10" lower. .22lr works just fine.
There are tons of intermediate and pistol calibers that you can run on a ar15 though

[dieselpower]

do a search, "how many uppers on an AR15 lower" and you should see a list in someones post.

[Sonic_mike]

5.56,22lr,6.8spc will work on the same lower.

[rojocorsa]

Don't forget about .458 SOCOM, .50 Beowulf, or 6.5 Grendel.

[Halfey]

I had no idea thanks for the insight

[rattlesnake_nm]

5.45x39

[dieselpower]

7.62x39
9mm
.45
243
.450
410ga

[steelcore]

So you can buy a 5.56 rifle and put on a .22LR upper for plinking... Can you do the opposite, or is a factory .22LR lower built any different? (eg: hammer strikes softer and may not ignite a centerfire primer? magazine well different?)

The reason I ask is because it would be easy (on the wallet) to buy a Colt .22LR from Big5 and later buy a 5.56 upper.