well i've seen some excellant examples that are just surprising,
but majority of them involve some core original (or reproduced) metal parts enclosed in 3-d printed receivers,
or they simply gather essential parts (barrel, bolt carrier, recoil spring) and remaining ones they made their own to make their own "plastic" version of original firearm,
and believe me some of the idea they have are so mind blowing...
for example, identify this, it is a 3-d printed shell of an actual firearm
View attachment 110359
apart from this they also make their own attachments to be affixed on actual firearms like their own sights, carrying handles and so.