Here's the answer to my question regarding why the second cylinder:

If you plan on shooting .22LR, make sure it does come with a .22LR auxiliary cylinder as you CANNOT shoot .22LR out of a .22 Magnum cylinder. It is not like shooting .38 special out of a .357. The .357 magnum is simply a lengthened .38 special case loaded to higher energy, which allows the shorter .38 special case to be safely fired in a .357 chamber.

The .22 WMR uses a larger case than the .22 Long Rifle, both in diameter and length. The .22 WMR case is a lengthened version of the older .22 WRF. The .22 WMR's case is thicker than that of the .22 LR, allowing higher pressures. The combination of more powder and higher pressures gives velocities over 2,000 feet per second from a rifle using a 30-grain bullet, and 1,500 feet per second from a handgun. A .22 WMR round will not fit into the chamber of a .22 LR firearm but is possible to chamber and fire .22 LR rounds in a .22 WMR firearm. This is potentially hazardous due to the difference in case diameter. When fired, the .22 LR case expands in the chamber, which can cause the case to split open or become stuck. Also, the long rifle bullet will travel in the magnum chamber unsupported for .4" before entering the barrel causing leading in the chamber.

So the best way for you to shoot both .22 LR and .22 Magnum is for you to buy a good S&W model 34 after you get your model 650. Which is what I did. After all - - life is too short not to indulge yourself once in a while.