Cool. But don't count on pressure signs. The 'normal' pressure signs we observe are based on 'normal' powder characteristics. You aren't using a normal powder, and not positioning it in the case volume normally. By the time you get pressure signs, you might already be taxing the gun, the brass, and the bullet. Just be smart and go slowly. Don't guess, don't draw conclusions prematurely.
We don't use QuickLoad to determine load data, but it's handy for comparison. I ran Blue Dot in your application. It certainly isn't linear. Maybe you can try a few more grains at most, but don't push it. You already have an accurate load.
Using handgun powder to reload rifle cartridges (especially with cast bullets) was very common 100 years ago for hunting. Handgun powders were easily purchased and there were several choices. But rifle powders were more scarce. And casting lead bullets was still a common skill. Published manuals up to 1960 had lots of loads, even the NRA listed them, but today only a few list handgun powder for rifle cartridges. Hodgdon still has some. Alliant had it for 2400 but I see it's mostly gone.
One thing they learned 100 years ago, soft point jacketed bullets can leave the jacket in the bore with handgun powders, the lead core leaves the barrel by itself and often hits the target. As we see in the QuickLoad model, pressure peaks high within a few inches of the chamber but then drops to about 200psi at the muzzle. With such low pressure, friction captures the jacket while inertia of the lead core continues its path. FMJ doesn't have that problem. That's why load data like Lyman usually addresses lead bullets. Alliant and Hodgdon only FMJ.
For instance, go to Hodgdon online data, click on Rifle, drop the menu down to 223 Remington, click on 55 grain bullet. You'll see Clays, Titegroup and Trail Boss listed. But when you open the data for those three powders, only FMJ is listed. Given the completely covered nose, it can't lose its jacket.
Have fun but keep sane.
