Developing a hand load for an existing hopefully regulated double rifle

How do you do it?

For me it's a combination of developing a load with the right bullet, Achieving a right velocity. And reasonable accuracy with reasonable regulation.

Developing the handliads.

I make up four cartridges with a range of powder weights, one grain increasing in powder weight. For each four cartridges.

At 50 yards or 100 yards, shoot the starting load, from clean harrels, one right barrel, one left barrel. A few seconds gap between shots. So the barrel warmth is consistent. Checking the velocity of each shot. Ideally identify each bullet impact. Gunmaker ranges use a video camera and recording for this. If one has such sophistication. The second two shots can be shot reasonably soon after. Otherwise it might be necessary to mark each two impacts.

Mark the bullet impacts of all four shots.

Clean the barrels. Using another target, shoot the next one grain increment four cartridges. And repeat. Continue as before.

Hopefully find a decent regulation load or loads. Hopefully one or more loads shows acceptable individual barrel accuracy and the two sets of two impacts overall accuracy , and regulation. Ideally two sets of two impacts an inch or so left and right apart and not crossing.

With my 9.3x74R U/O Tikka; I have the top two impacts a half MOA or touching, a inch above similar fired from the lower barrel. Its scoped so much better accuracy is possible. With self regulating barrels and barrel wedges, I can regulate the barrels to my desired handload.

Better would be 2x 3 shots. If ammunition components allow and accumulated recoil tolerance. Say 5x 4 cartridges or 5x 6 cartridges might be testing recoil tolerance for good shooting. Depending on how heavy the recoil is.

Standing rest if possible.

I narrow down the powder charge. Then do the 2x 2 shots or 3 shots, two or three times to double check.

If regulation and accuracy has been achieved, ideally shoot the load; 4 shots, at 50 yards, 100 yards, 150 yards, 200 yards, maybe further.

If the original test loads were not accurate or not acceptable regulation, try a different powder, bullet etc.

I don't have any double rifle so setup, but if it has QD sights, and additional dot points, scopes or other, different loads, bullets, might be able to be setup, using a different sight if it is necessary. Or better of course the original express sights, scope etc work with additional loads.

So far once I've found one load that works, I've just used that.

What do you do? What process or methodology do you use?