As a former firearms curator, I don't believe anyone will be fondling a Glock or XD in 100 years since it is doubtful the polymers used in their manufacturer will maintain their integrity that long. It may be possible to preserve our modern "plastic guns" in a climatically controlled inert atmosphere with nitrogen scrubbers. For most folks, they will crack and pieces break off as they become brittle with age and exposure. I love iron, steel, brass and walnut. Probably half of my "working collection" is 100+ years old. One of my youth small bore shooting team was astounded when he learned that the BSA Martini rifle he has shot a near-perfect 299 with was 104 years old when he did it.