With the filters, sterile is speaking of the packaging, not the actual filter, no matter what, as soon as the air touches it, it's no longer sterile, as soon as you push unsterile oil into the filter does it become non sterile? No.
Think about this, you take an unsterile solution, and it goes thru the filter, it's the process of the oil going thru the filter paper that removes particles, bacteria etc.
BA DOES NOT STERILIZE A SOLUTION. BA is an anti microbial. It's a multi use vial, a pin that touched the air is no longer sterile so you continuously put an unsterile needle into the oil, thru the stopper. BA prevents any new growth of bacteria it doesn't sterilize, and baking doesn't do anything.
If you wanted to bake it so it was sterile, it would be at such a high temp it would most likely run the gear.
You don't need to run IPA thru the filter, you can wipe the outside with 91% IPA if it makes you feel better but it becomes sterile once it passes the filter and everything is removed.
Just use a .22 whatman zap cap bottle top with a pre filter, but no the sterile are not really any different, as soon as you open the package and pull it out to attach to your barrel it's not sterile.
If BA sterilized a solution, you could simply make your solution with BA, then let it drip thru a coffee filter and it would be good to go but that's it the case. Email whatman and ask them the difference between sterile and non sterile filters!!! Ask them if the are any different as soon as you touch then, breath near them, or attach to your syringe barrel. It's not like they are sending you dirty filter papers, it's the oil passing thru it that removes everything.
I've used both in .22 and .45 sterile and not, and in close to 12 years zero infection, any on who's used it, zero infection. Be more concerned about sterilizing your working area as best as you can, and making sure that anytime a filtered solution leaves the filter its into a sterile vial or media bottle. Then draw out using a sterile instrument, and use something like HIBICLENSE before touching anything.