Round or flat bottomed NMR tubes, what's the difference?

Some researchers in the past have stated that round bottomed NMR tubes are superior to flat bottomed because they shim better, while others couldn't tell the difference. A researcher recently wanted to know what the differences were between the two types of NMR tubes and which type would be better for his experiments.

To answer his question, we have to take a brief look into a past experiment of about 20 years ago, that involved a study in determining the strength of NMR tube bottoms. The experiment involved dropping flat and round bottomed NMR tubes from a height of about 5 feet, to observe any changes in the tubes bottoms. After doing this to 100 tubes of each type, the flat bottomed tubes outperformed the round bottomed ones by not breaking as many bottoms. Round bottom tubes would break more often, because the round bottom tubes had a significantly thinner glass wall than a the flat one's. At the same time, shimming experiments revealed that when the experiment only contained flat bottom NMR tubes, that shimming between the tubes took the same amount of time as with round bottom tubes. There was only a difference in shim times, when round bottom tubes were mixed up with flat bottom ones.

So to answer the researchers question, if you already are using NMR tubes with round bottoms, for the sake of faster shimming times, buy round bottomed tubes. If all your tubes have flat bottoms, continue to use flat bottom tubes. Just don't mix up flat bottomed ones with round bottomed ones, if shimming times between tubes is important to you.