It's hard to do anything that alters an original gun and not devalue it. Yes, D&T will devalue your gun.

Zeke,
I think the best thing would be to post a picture of it. I think that we could get a much better idea of what it might do to the value.

I have a similar issue on a HW that has a very nice exterior on a 32rf barrel. It's been relined to 22 Hornet so, I don't think it would hurt it's value but, I just hate to drill on the outside of a nice old barrel that has no holes in it. If I ever do drill it, it will be for scope blocks so, at least it will still have a older flavor to it. Not 1880's but early 1900's.

Another option is to rebarrel it and then you can do what ever you like to the barrel, save the old one and then you can sell it either way or as a two barrel gun.

Frank

The first hole you drill will devalue it from $150 to $1000, depending on the rarity of the configuration.  The next 3 won't devalue it, as long as they're in the right places.  Then, after that, about $25 to $50 per hole.

It costs about $500 to rebarrel a rifle.  Maybe even $750, depending.  Many times it is cost effective to take the loss on an original, compared to taking the barrel off, selling it, or keeping it to return to original and then rebarrelling.  I don't know that it is right, it is just cost effective.

I have sold a couple of guns that were too nice to break down for an action or modify.  The first one I did this to, the seller immediately used the nice action to build a new sporter.  I sold a very nice .38-55 high wall a couple months ago because it was too nice to use for the action.  Plus, it would shoot under 2 inches at 100 yds.  The buyer told me he was going to modify it.  So, sometimes trying to do the "right" thing, doesn't work anyway.

On the other hand, I sold the first nice collectible single shot I ever owned many years ago because it was in an obsolete caliber.  The fellow told me later he was going to reline or rebarrel it.  I just traded back for it this spring, paid 20 times what I originally bought it for.  It was in similar condition to when I got it.  Sometimes they stay intact.  Now, I keep thinking about relining or rebarreling it.

dave

If you are worried about devaluing the rifle why not glue them on? A well known collector I know has done this many times. He uses Black Max. Just degrease the spot and glue them on. He has had no problem with them shooting off in 32-40 or 38-55. When its time to remove the blocks a sharp rap and they come off. After cleaning the glue off with acetone it is as good as new.

40 Rod