Roger that! A chronograph or better yet, a Lab Radar makes finding a double rifle's sweet spot of velocity a lot easier! I mean an awful lot!
Another benefit of recording velocity of each shot, for each barrel, is to monitor for extreme spread and mean velocity spread.
A Frames may in fact impact differently than DGX at the DGX regulated velocity. Powder burn rate may affect this as well. Hornady may use a proprietary powder and primer not available to reloaders.
Using established load data ( I subscribe to loaddata.com It's worth it) start lower in velocity and shoot 2 to 3 rounds from each barrel. Record those two groups. Assuming right barrel impacts low and left and vice versa for left, you have a baseline! Gradual increases of powder, within the listed range of load data, and the two groups should eventually merge.
If you can't get them to cross within the load data range for your powder, a different powder should be tried. I would try a slower burn rate powder if you have room without too much compression.
For powder, I like newer ones that are much more temperature stable. Africa can at time heat your barrels so much so that they are uncomfortable to touch! Add 40 to 60 degrees to when you developed your load and older favorite powders may burn faster, increasing pressure, resulting in increased velocity. There goes your regulated loads! If your load was at a maximum mean pressure at 65 degrees using a temperature unstable powder, at 105 degrees, your action may not want to open!
I used H4350 for my bolt action 375 H&H and will use it to start to develop loads for my .375 double. It is temperature stable and once again available.
Bottom line is measuring pressure is possible using strain gauge devices such as Pressure Trace. It is however not necessary for developing loads that have much load data available.
I hope this helps!
