If your primers are seated 'high' - i.e. they're protruding from the back of the round - it's entirely possible that in a semi-automatic rifle, the firing pin may strike the primer before the bolt has locked into battery. The results would be what's known as an out of battery discharge, which is almost guaranteed to damage your gun and may even blow it up, sending parts of it into you.
Double Charges - if you're loading with a single stage press or dippers, it's fairly easy to accidentally forget what stage of loading you're at, with a pistol cartridge, and dump another charge into it. Given that you've just given it twice the normal powder charge, you should not be surpised if your gun becomes a hand grenade. This is unlikely in rifle cartridges, as they normally take so much powder that a double charge would spill out the top.
Light charges - Similar to double charges in effect, but this affects rifles as well. It is possible to have a load light enough that the powder lays more or less horizontal in the case. When the primer fires, a jet of flame is sent over all of the powder at once. Instead of a controlled burn, you have a detonation that can kill, even when the bolt is locked into battery correctly. Such a load is reputed to have blown the bolt backwards out of a bolt action rifle, into the skull of the little girl who was shooting it, killing her. Her father had decided he was going to set up some gentle, light 223 loads for her to shoot, without knowledge of what a light charge can do.
Obtaining load data for your ammunition
I found a site that lists a number of different loads: http://www.reloadersnest.com/. Even if you're only thinking about a caliber, it's a good place to get some ballpark figures so that you can compute per-round costs, etc.
However, contributors to thegunwiki.com are welcome to keep logs of their reloading activities on this site for the benefit of others. These logs will, by their very nature, include load data and performance results. No guarantees are made by thegunwiki.com as to the safety or function of these loads, as we have no control over what people write down.