I just bought a Zenith 5RS. I’ve noticed some people change some parts out right away. What is good to change or what are they changing?

BLUF: I would buy and run the MAD Bolt. That's it. Anything else would be spare parts purchases.

Details:

I ran down this path and learned the Zenith parts worked as good as the German parts. OMG!!!

I bought a SP89 carrier and an F bolt... and now the high dollar F bolt is a spare while I use the German carrier with a MKE bolt. It *might* be a touch easier to charge but that could be in my head. The bolts are identical to my eye outside of the roller holders.

Maybe I was lucky but the bolt gap didn't change with either bolt.

The MAD Bolt with a spring type extractor spring makes so much sense. I might even sell my F bolt to buy one.

https://www.franklinarmory.com/products/franklin-armory-bfsiii-binary-firing-system-iii-trigger-for-hk

No reason to run a MAD bolt or replace any parts on your zenith. Submit a form 1, pick up some spare mags and buy ammo and see what parts if any will make shooting it more enjoyable after shooting it for a while. (red dot, different stock, weapon light, etc...)

The main thing to do with a Zenith is to verify that the specific gun that you bought is a good one, as soon as possible. There seems to be more than a little bit of variability, regarding their QA and QC. The main problem areas seem to be the magazine well, causing loose-fitting mags fore and aft, and canted sights. So, if you get a Zenith with a good receiver, you should be good to go.

Good advice. I got one with canted rear sights and they just sent me a whole new gun. The next one was better, but still slightly canted. It zeroes just fine though, so I didn't make a fuss out of it.

I prefer a red dot on mine using the supplied mount and a UTG low picatinny riser. Clears the front sight hood and is still QD. I Form 1'd mine and right now it's wearing an A3 F stock, but I generally prefer the A2 stock for actual shooting.