Looks like you are making good progress. If you are using the 122 gr FP bullet shown on their website, you may need to use shorter OAL than the typical RN OAL due to the nose profile. If your dummy rounds is dropping into the chamber freely without hitting the rifling and feeding reliably from the magazine, you are ready for your powder work up and range test.
When I am loading Missouri 125 gr RN, I need to use shorter 1.080"-1.100" OAL due to longer bearing surface (part of bullet base that rides the rifling) of the bullet and shorter/rounder nose profile. If I use the typical 1.125"-1.135" OAL, bearing surface will hit the rifling in some pistol barrels.
Look at the different bearing surfaces of each bullet as they'll determine different bullet seating depths. For 125 gr SWC bullet that's similar to the Dardas FP bullet, 1.045" OAL passed the barrel drop test without hitting the rifling and fed reliably from the magazine. But because the bearing surface is much longer and bullet base gets seated deeper in the case neck to produce higher chamber pressures (see blue arrows with comparison case bulges in the picture below) and
Hodgdon CN load data used 1.125" OAL, I used .3 gr below start charge and .2 gr below max charge of Hodgdon's current load data when I conducted my powder work up with W231/HP-38 (I used 3.6 gr as my start charge and 4.2 gr as my max instead of published 3.9 - 4.4 gr).
Note: If you are using bulkier powder with deeper seated bullets, calculate the powder fill to bottom of seated bullet base to ensure you are not compressing the powder charge. Since W231/HP-38 is a dense powder, even the 4.2 gr charge and 125 gr SWC bullet at 1.045" did not compress the powder charge.
Using G22/G27 with LW conversion barrels, I got reliable slide cycling even with the start charge and accuracy was obtained from start to max charge with slightly more recoil than my comparable RN loads.
If you are using 1999 Winchester load data for 125 gr RN for the 122 gr FP bullet, you probably won't need to reduce your start/max charge. If you are using current Hodgdon load data for CN bullet, I would work up to 4.0 and see how things are.
Keep us posted on your powder work up.