A very high % of those 880s and 881 have rocking blades due to the contact point of the lock more than anything else. Most of the ones I examined closely contacted more in the middle third of the lock instead of the lower third as it should. On some, including my own I was able to get this out but it required taking them apart and taking down a bit of contact in the middle so only the lower part of the lock contacted the blade.
Now the good news on those usually built this way is that many times the lower as well as the middle did contact the blade so you could take out the middle and still have a contact, but in time the middle should wear to eventually reach that point on its own.
On two, including one I owned it was necessary to modify the contact due to the amount contacting in the middle third though. I don't know why Buck let so many out the door with this but I saw quite a few there at the peak of the sales in those models. I also noted on more than one forum that others noticed this rocking blade syndrome also and usually when one came up for sale this was the first question asked. You typically saw replies where the owner had to admit there was a tad of blade play. The ones that were solid were highly praised though.
STR