I'm in the process of having a custom .376 Steyr put together on a Mark X and just got the barreled action back from McGowen. It's going to be an "all weather" rifle and I am debating on the finish. Are there any REAL WORLD advantages/disadvantages when comparing Robar's NP3, Electroless Nickel or Nickel Boron? I like the yellowish hue of one of the matte nickel finishes but the NP3 looks pretty sharp too. Thoughts?

Just to muddy it up a bit for you...... What about a hard chrome finish? I have a Brown Precision with Metaloy hard chrome finish and it's tough. There's a few pics in the link below.

https://www.24hourcampfire.com/ubbth...t_a_cool_new_to_me_Brown_Pre#Post6825927

NP-3 is the best Nickle type finish you can apply to your firearm in my opinion, especially Handguns but when doing rifles i have always used Armaloy . Now if I'm doing a rifle it would be Cerakote

IMHO, hard chrome or NP3 would both do well I have guns finished in both and there is little difference in the field.
Nickel-boron sounds good in the literature, but I have no experence with it. It is apparently popular with AR-15 shooters who have their bolts and bolt carriers plated with it.

RAN

I have had, NP3, Electrolees Nickel, Teflon, and parkerizing. NP3 is a real slick good looking finish, but I didn't find it particularly tough. The plating on my bolt wore down pretty quick.
Matte Electroless looks great and stands up well, but again a bolt plated with it will wear fast.
A good parkerizing finish will last as long as your alive but doesn't have that wow factor.
Teflon isn't as tough but looks great. My last Custom has teflon barreled action with a parked bolt and its holding up real well. Lots of good choices out there. I haven't had a chance to try out ceracote but the reports on it are all positive.