In order to value a special order gun, it would be best for you to get the gun to someone who knows them very well so that they can evaluate it. Pictures would certainly help people here to give a more detailed opinion. 20" 33 WCF are certainly not common and could be modified after it left the factory. Getting the factory letter info from the museum would be the place to start. If they confirm the special features, that's a big step.
Is it a 20" short rifle or a 20" carbine? Does it have any other special features (pistol grip, checkering, engraving, special sights, upgraded wood, etc)? And, probably most important, what condition are the metal and wood in? Has it been modified or refinished?
If you want to email pictures, pm me your email address and I'll send you mine.
This is good advice. more rare than a 1886 trapper would be an 1886 that hasn't been modified in it's history at some time. They weren't made to be collectible, they became that way over years of use and abuse, making survivors in good shape collectible.
Typically, a trapper model would have a shorter barrel than 20", and I find no indication of them as available as a standard configuration. Special order would certainly make it a 20" gun, but a letter would need to verify that pedigree.
Condition is one of the main components to value and a refinish will hurt that value quite a bit. You do need someone that knows old Winchesters to validate it's originality, otherwise you may have a serviceable old 33 WCF that would be fun to shoot and hunt with...
Post up some pictures!
![[Linked Image from i.postimg.cc]](https://i.postimg.cc/G9RDVKXr/DSCN4329.jpg)
