hylander, Your specs seem pretty good. Try your cylinder-to-bore alignment again. This time rock the cylinder from side to side. The bore should align somewhere in the range of the "side play". Contrary to popular belief, a rock solid lock-up is not good unless you are one of the very lucky ones where the cylinder-to-bore alignment is perfect at lock-up. The bullet will force the horizontal alignment of the cylinder with the bore providing there is enough slack. If it doesn't align, the bullet will shave and you'll feel some spitting from the cylinder gap. Accuracy suffers too.
Now try your cylinder gap again by holding the cylinder to the rear, then to the front. This will measure end shake (front-to-back movement). Zero end shake with a free moving cylinder is best. The end shake should not exceed a couple of thousandths (difference in front and rear measurements).
Belt Mountain base pins will work in most guns. The pin is slightly larger in diameter than the factory pin and tightens up some slack from cylinder-to-pin movement. In some guns, they actually make accuracy worse. The factory base pin is loose on purpose. Just like side play, a little looseness may be necessary for vertical cylinder-to-bore alignment. Again, the bullet forces vertical alignment as long as there is enough slack from the base pin. Primarily, the BMBP will prevent launching the base pin. If your base pin stays in place, save your money.
Timing is a sequence of events that starts with cocking the hammer and ends when the trigger resets after the gun has fired. Basically, if your cylinder rotates and locks when the hammer is cocked, your timing is OK. Alignment is quite a different thing from timing, however in extreme cases, timing can be the cause of bad alignment. This would be when the hammer is cocked and the cylinder is not rotated far enough for the cylinder stop to lock the cylinder.
