A stuck bullet in a revolver barrel can be removed easily by driving it back into the cylinder (if the cylinder won't open) or back into the cylinder window if the cylinder will open. A stuck bullet in a rifle barrel is another matter for another post.
Squib loads usually are the result of a lack of powder in the case and that can (but rarely) happen with factory loads. The primer has enough force to drive the bullet into the barrel or lodge it between the barrel and cylinder. Bad or damp powder could cause a squib also, so moisture could cause a squib. For that problem, nail polish would be perfectly fine as a seal for the primer and case mouth, but with factory ammo there is no way to know if the damage may have already been done in storage before the customer purchased the ammo.