Rob, have you tried "regulating loads"?

1. Choose the bullet and powder you want to use.

2. Start with the min. charge. Then load pairs of shells and work up in 1 or 2 grain increments.

For example:

180 grain Hdy, Reloader 22 powder

2 shots at 56.0 grains powder
2 shots at 57.0 grains
2 shots at 58.0 grains
2 shots at 59.0 grains

That will produce a pattern on the target that you can use to see where the barrels begin to converge. Typically the pattern will be V-shaped with the barrels moving toward convergence as the powder charge increase. POI will also drop as the powder charge increases.