With the growing popylarity of PCC, it seems everybody are building their 9mm AR carbines as lightweight as possible. Rifles on the other hand still seem to lean towards a heavier setup.

Is this a correct observation, and if so - why is it so?

The benefits of manouverability with a lightweight carbine would also apply for a rifle? Or is it because PCC matches are more "CQB", and rifle matches don't face the same obstacles?

The benefits of a heavier rifle mitigating recoil would also apply to a PCC, would it not?

Anyway, thank you all if you'd like to give your two cents on the topic.

A 556 AR requires more metal than a 9mm PCC AR, so it will always be heavier

There’s numerous LW threads in the AR forum and plenty of people focus on weight when configuring their rifles, so I’m not sure where you’re getting that.  Can you elaborate any further as to what led you to this conclusion?

Uhhh, pretty sure that’s not accurate.  Barrel may be slightly lighter weight given the lost material with a larger bore.  BCG is pretty much a wash.  Same for receivers and handguards.  Buffer is typically going to be heavier.

I’ve handled more than enough AR based PCCs and can’t say any were noticeably lighter weight than a similarly configured 5.56 gun.

ETA:  Here’s an example of nearly identical guns, 5.56 vs 9mm.  The 5.56 gun is lighter weight.

5.56:  6lbs 9oz
https://www.springfield-armory.com/saint-series/saint-victor-ar-15-rifles/saint-victor-556-ar-15-rifle/

9mm: 6lbs 15oz
https://www.springfield-armory.com/saint-series/saint-victor-ar-15-rifles/saint-victor-9mm-carbine/

My PPC 9mm AR is actually heavier than my pencil barrel 16" 5.56

Mostly my fault because I am using a steel mag well adapter on a standard forged lower, excessively long 8" barrel, steel Colt stick mags and flaming pig blast can.  

If I swapped to a dedicated lower, Glock mags,  a shorter barrel and smaller muzzle device then I think it would only be marginally lighter for the reason a prior poster said regarding the larger diameter barrel and heavy buffer.

I have noticed the popularity of LW rifle builds outside of the competition scene, and I prefer them myself, but I still see a lot of heavy rifles at my local IPSC competitions (JP in particular, heavy barrel, handguard, billett receiver). LW bolts being the exeption. I was wondering if this was because the trend 10+ years ago was a heavier setup and the move to LW competition rifles just takes time, or if the heavier setup is more beneficial in a rifle match than a PCC match.

This is why I was curious if my (local) observations were representative for a "modern competition rifle".