This capper worked well for me, it passed the king crimp gauge
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The caps are lined with plastic. The O2 diffuses through the plastic.
I decided to buy a bench capper with a bell made from a chunk of metal or machined bell. My LHBS didn’t have one so I bought this. Amazon.com: North Mountain Supply Heavy Duty Bench Bottle Capper - Compatible with 2 Sizes of Caps - All Metal - Professional Grade - Made in Italy It hasn’t arived yet.
I spent a number of years supplying specialized coating for gas barrier resistance and can tell you that the amount of gas diffusion through a plastic bottle is FAR greater than through the cap liner. It is a matter both of type (PVC is a poor barrier vs PE), surface area. thickness and the presence of any O2 scavangers. I believe that all beer bottle cap liners are PVC, have an O2 scavanger (says right on the label) and have a permeation pathe that is measured in CM, not microns. Add to that the extremely small surface area, the partial pressure difference between the outside of the bottle and the inside and the relatively short time between bottling and drinking and I am more than certain that the caps are not an issue for oxidation vs bottling practices.
I’m convinced that injecting CO2 ( how homebrewers force carbonate) is far more detrimental than any other process. I’ve never had an oxidized beer in a bottle that I bottle conditioned in the short term, and some last for years. On the other hand I’ve had force carbonated beers bottled with a counter pressure filler barely last weeks. Maybe it depends on the quality of CO2, ymmv. Commercial brewers bubble CO2 through the beer under a little head pressure so the oxygen barely dissolves.
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Does the O2 scavenger have a shelf life?