QuickLOAD's powder data is based on one lot of powder. Burn rates vary several percent with different lots, so you sometimes need to take a chronograph and adjust the powder. See Chris Long's information on tweaking QuickLOAD here
QuickLOAD's default case capacities are usually on the small side. Until you get a measured case water capacity for cases fired in your chamber, you can expect the results to be on the small side. But, again, you may also need to tweak as above. I've seen quite a number of instances in which QL allowed a charge above book maximum, too. This should not be a surprise as you can find quite a number of examples of load ranges in manuals wherein one manual's maximum load is below another manual's starting load for a same-weight, similar construction bullet.
Finally, QuickLOAD was developed primarily using bottleneck rifle data, and it doesn't play quite as nicely with straight wall cartridges. I recall the QL manual mentions one example where the capacity of a particular straight wall cartridge had to be increased several percent above reality to get good predictions. It is also the case that in small capacity cases it isn't unusual for primers to dislodge the bullet from the case before powder pressure starts to build, altering the burning volume. The .22 Hornet is famous for this, and I've seen a lot of evidence of it happening in .45 Auto, too.
Bottom line is to get out the chronograph and see what you get. Try tweaking by Chris Long's method and see what you come up with.