The default values in QL need to be used with some skepticism. Models have context and you don't know which details in the donated model are the same as yours. With 223, case volume varies widely. Many will load bolt guns to 556 pressures with good brass life. That CCI 400 primer probably won't work with that trick. I matched this one to the Hodgdon data by using a typical case capacity for the Lake City brass I use. Winchester should be similar. Not sure about Remington.
Hodgdon gave 3234 fps @ 53,300 psi. After adjusting the case capacity, this model gave 3233 fps @ 52,088 psi. The fired case capacity is generally used for these models. In addition to the manufacturer and individual lot, the chamber volume of the gun matters as well. With 223, these are not subtle effects, they're very noticeable. The close relationship between the bore and case cross section in the 223 case makes it especially sensitive to seating depth. The big change in pressure happens when the bullet first contacts the lands. That's not very likely to happen with a 55 grain bullet in a commercial Remington chamber. Bringing the bullet forward increases the usable case volume and reduces the compressed load crunch.
Powder lots vary and powder moisture can change with storage. Both can have large effects on pressure and velocity. Barrels will exhibit different start pressures. Factory Remington, Savage, and Ruger often give lower start pressures. This reduces the peak pressure and velocity. Custom chambered or "test" barrels will give higher pressures and velocities. What barrel was used is a good thing to check with reloading manual data.
A buddy had problems with that bullet in that gun. Great 100 yard groups. Couldn't hit anything at 400. Applied Ballistics Analytics gives a Sg < 1.1 for that bullet at that velocity from a 1:12. If you're going to push Sg limits, 223 is a good place to do it but that might be a bit too far. We were at a DA of 2000'. A flat base 50 grain bullet solved his problem. I'm curious about how that bullet will do in your gun, please report back.
