Thank you very much for your photos. It helped me to see that the tips you have in all of your pencils are different from mine. I gave it a closer look under my microscope, and I beleiev that my tip is brooken. Also, there is “click” sound everytime I click to advance lead, which concludes that my pencil is broken. I think that what you have referred to the missing metal part of my tip as missing “sleeve.” I though that sleeve referred to the rubber insert.
Thank you sincerely for your help, really greatly appreciated. I also like your early 770s a lot. Nice colection you have.
I also just found this discussion about the 770s with nice images: