What causes a rifle round to close tightly in the chamber?

Answer 1

Not certain that I understand exactly what you are asking. If you are having a problem in that a cartridge will not fully seat in the chamber, it could be a couple of things. First, check that you have the correct ammunition for the gun in question. While that sounds very basic, it happens more often than you think. Next problem could be a foreign object in the chamber, or fouling from being shot. Clean the chamber with a chamber brush and powder solvent, check the chamber for things like a section of a cartridge case that tore off, and is stuck in place. Last, check the extractors- see that they are clean and free to move. Some firearms are designed to have the extractor slip over the rim when loading- if not free to move, the get caught behind the cartridge.