So, you cut off the end of the nozzle on a tube of silicone caulking material. You squirt the contents where required, and the job is done, but the tube of caulk isn't. Saving that partially used tube of silicone goo for the next time you need it can be difficult. Cap the nozzle as well as you can, but I'll bet that in a month or so, when you need to use it again, you'll find that the nozzle is clogged with solidified caulk, thus rendering the tube unusable.
The reason is that the caulk solidifies in the presence of humidity. It seems that no mater how well you try to plug the nozzle hole, somehow airborne humidity gets in to do its nasty work.
I had to cut off more and more of the nozzle to get down to unreacted caulk. When I finally hit pay dirt, the nozzle hole was a little bit more that 1/4-inch in diameter, making for rather imprecise application and project neatness. In any case, I wasn’t quite ready to apply caulk, so I faced the problem of preserving the usability of the soft stuff that was still down in that nozzle hole. I certainly didn’t want to have to cut off more nozzle later only to end up with a 3/8-inch hole.
I put the tube in the caulking gun and put the gun in the bench vise with the open nozzle oriented upward. Desperate to find a good seal, I hit on the idea of putting a few drops of light machine oil in the hole to keep humidity out of where I didn’t want it to go.
The result – it’s been two weeks since the experiment started and the caulk hasn’t yet solidified. I just thought you’d want to know.