There is a cartridge database with dimensions and max pressure, a bullet database with dimensions, weights, and shot start pressures, and a powder database. The databases are real comprehensive. There is no primer database, probably because the differences in primers are outside the accuracy of the program.
You can adjust barrel length. Like any other program, accuracy depends on the quality of the data, and the mathmatical model. You don't want quickload to be the final word, because it can be way off. it can also be real close. It shines in areas where most other simulators shine. It does a great job of showing the effects of manipulating your loads, and can be tweaked to agree more closely with real world loads. I usually try to compare it with pressure tested load data from the manufacturers. The truth is somewhere in all of it, with my chrony being the most reliable source of data.
I use SPICE in analog circuit design. It's a real powerful tool if you know its limitations. If you don't, it will get you into a bunch of trouble.