I'm well aware everyone says "don't do it!" when it comes to twist off beer bottles; however I've had good results (100% success) with Shiner Bock bottles. We started looking at the profile of the twist off bottles we had on-hand, and noticed they all differed slightly in their design; some have a larger "grip lip" below the threads that allows the cap to grip some bottles better than others. Other bottles, the threads of the bottle are shaped more like a traditional "twist-less" bottle, negating the need for a grip lip. So part one of the theroy is that some twist top bottles might be more appropriate for home brewing than others, based on the shape of the capping area.
The English Cider bottle would likely be a better home-capping cannidate due to it's deeper grip lip than the Makeson Stout.
Another thought that popped in to my head was that we're using overstock "Full Sail Brewing" caps, which I believe are a twist-top brand, and might have a longer "skirt" (the part of the bottle cap that's ruffled and hangs from the side) than consumer-use bottlecaps. Perhaps the caps supplied to brew shops are intentionally "short" so they can't appropriately wrap around the threads of a twist-top bottle. Face it, brown brew bottles have to be a high profit-margin item. Part two of the theroy is that skirt length of the bottle cap is a determining factor in pressure retention.
Part two is easy to test; simply pound flat caps for home brew bottles, and twist off bottle caps, and measure.
The full sail cap is a twist off cap, measuring roughly 1.5" across, while the Dr. Pepper cap is a traditional cap, also measuring 1.5". Not pictured is a Thomas Kemper root beer twist off, also measuring 1.5". (It's impossible to pound them completely flat due to the rubber seal attached to the underside)
Part one though, requires seeing how much pressure each thread profile will hold using a standard bottle cap (found at a home brew supply shop). Beer takes a long time to brew, and is expensive to make. As I understand it, commercial beer is pressurized at about 25-35psi; I'll assume home brew doesn't get above 40psi*. As an alternative to beer for pressurization, I'd like to use baking soda (or powder, whichever has a better cost/gas ratio) and vinegar. The question is, how much do I add of each to an empty bottle to pressurize it to 35-40psi? This should be a simple chemistry equasion of figuring out how much CO2 is produced when you mix a mol (MOL?) of Vinegar and a mol of Baking Soda (powder?) together... and then? This is why I ask the geek beer community.
Once I can figure out the proper portions, I can cap and compare bottle profiles to show what types of bottles hold their pressure, and which leak.
*although I do have some hard lemonade I made, and then primed with sugar (in the 5 gallon bucket), and 3-5 pellets of champagne yeast (per bottle), which is probably 50psi, causing the caps to bow upwards.