My guess is your bolt isn't fully closing on the live rounds. In an AR, if the bolt doesn't lock up all the way, the carrier is held back out of battery slightly, and that will cause light strikes or prevent firing pin contact alltogether. You can verify this by looking at the position of the bolt carrier through the ejection port; look at it with the bolt closed on an empty chamber, then compare it's position when you get a light strike. Causes can be a dirty chamber, tight chamber, out of spec ammo, too strong extractor spring, just to name a few.
If you verify this is correct, first thing I'd do is inspect the chamber and locking lug area for excessive fouling and debris, second thing is to try different ammo, like whatever your friend used.
Also, since you're new to ARs you may not know this: when you chamber a round (on a correctly functioning rifle) the firing pin makes light contact with the primer due to inertia. If you eject a chambered round, you'll probably see a light firing pin strike on the primer (very small, way too light to set it off). This is normal.
I doubt it's the Rise trigger. I only have a couple but they seem to be good to go. The fact that you can fire the gun by dropping the bolt on a round in the chamber indicates the trigger group is working fine.
It is possible you assembled something wrong with the buffer tube and internals. Hard to say without knowing what you did.
I don't see any indication here of needing an adjustable gas block, other than that it's an AR10 and they pretty much all benefit from one. However that's a separate issue from what you're describing.
Last edited by Yondering; 03/09/20.
