When printing Avery 5160 or other labels or reports where the position of the items on the page is important, be sure the printout is not scaled or reduced in any way, otherwise the labels may not line up to the printed text correctly when the document comes out of the printer.
Whether printing labels from the web browser directly, or from Adobe Acrobat Reader, there is typically an option to "Scale" or "Fit to page". It is critical that this option be turned off so that the document will print at 100%. Below is an example of this setting in Google Chrome browser.
It's also worth noting that some browsers or PDF readers such as Adobe Acrobat Reader save these settings for the user, so be sure to verify the setting each time before printing.