What finish is the most wear - weather resistant?

I'm assembling a 35 Whelen 03-A3 and desire a tough finish.

My suggestion is Parkerizing like your 03-A3 currently has. I remember when Cerakote was the rage and now it's like a passing phase. No spray on/bake on finishes for me.

+1

Slow rust blue is another option. And yes, it's durable.

Nitride

Spray finish is down for me, good old Parkerizing is a up

Parkerizing is like blueing and requires oil to keep it from rusting..... but it is tough

Cerakote is more corrosion resistant, but can wear depending on what your doing with it - frankly I don’t honk most guys use thier rifles / shotguns enough to have it wear cerakote... military yes, and 25 to 30 years and it will show a bit.

Nitride is also good but more costly to do.

Here is a good quick read on the different types of finishes. https://www.omahaoutdoors.com/blog/ultimate-guide-gun-coatings/

Sorry, but I have seen cerakote wear through in one hunt of one week... Just riding in a raft touching the tubes.

That was my point.

The Cerakote on the military guns used everyday wore pretty good but we put them through hell and back, but I’ve not seen a hunting rifle wear like that yet...

Now if you ride a mule elk hunting for a couple weeks every year, maybe. Over time.

I have seen plenty of hunting rifles showing cerakote wear...