Also using the Lee Auto disk powder measure ( Pro or otherwise), you will rarely find any cavity that gives you the exact charge you are looking for. So you have to go for the cavity that gives you the charge closest to what you are going for without going over the max charge weight. I doubt you will find a cavity that will measure 4.5 grains exactly. You will probably have to settle on a cavity that could give say, 4.7 grains.
When you are first starting out in reloading, never load less powder than is stated and never exceed the max. As long as you find a cavity that gives you close to what your looking for and it isn't less than minimum charge or more than maximum, you should be ok.
I saw in your other thread where you were discussing your mold is throwing bullets that weight 134 grains instead of 124 grains. Over on handloads.com, there is load data listed for 136 grain lead round nose for 4.1 grains of Unique, or 4.5 grains of W231. Either one of those loads would be acceptable for your bullet. Kind of hard to get exact charge loads with the auto disk measures. Lee does make an adjustable charge bar.
http://www.titanreloading.com/powder...le-charge-bar-