Testing swing tops for carbonation

[C4PNJ4ZZ]

I bought a case of 12 1-liter swing tops last summer from my LHBS. I have used them on a few different brews and they never seem to carb as well as my other bottles (both 22oz and 12oz caps and 16oz grolsch). I'm going to replace the gaskets on them before using again. Is there any way I can test them BEFORE using them. I know people use the balloon trick to see if they are leaking, but I'd rather not abuse a liter of american amber.

 

[GrizlyGarou]

I've noticed the liter bottles take longer to carb than my 12 and 22 oz bottles.

You could always put some warm water in them (not hot!) then cap them and put them in the fridge for a while. As the water cools it shrinks, and when you open it there should be a vacuum. I used to do it at parties when people had beer in screwcap bottles, after a few beers it sounds pretty much the same as opening a regular beer then they drink water. Always good for a laugh or two...