It's recommended to learn how to use the
NIS function in world builder as this will allow you to preview and test the states, variables, and actions of a blueprint.
There are several reasons why simply moving a weapon from one thing may not apply correctly to another.
weapon\anim_table
The animation table controls what kind of animations a blueprint will use for its weapon. Most of the list is self explanatory in what its functions are. If you've use the sexton_dummy_mp anim_table you can see that most of the entries are blank whilst the su76_76mm_zis-3sh_gun_mp have them correctly filled out.
weapon\fx_munition_name
This is the action that will be played when the weapon hits something.
weapon\projectile
This is the projectile that is used by the weapon. The projectile in ebps must have the correct projectile_ext\launcher_marker otherwise the projectile will start from the 0, 0 point of the blueprint.
weapon\tracking\normal
This is how far and how fast the weapon can turn. You may view the extent of a weapon's tracking in world builder under the variables. Visually, a weapon may not exceed tracking degrees of its blueprint.
The Sexton uses a different system than the su76. Whilst it is possible to replicate it with the su76 it's much easier to just work off of a su76 clone instead.
1. Clone weapon\soviet\ballistic_weapon\su76_76mm_zis-3sh_gun_mp
2. fx_munition_name: shell_artillery
3. Clone ebps\projectile\german_105cm_artillery_mp
4. Replace projectile_ext from su76_at_76mm_shell_mp
These changes will visually have the su76 fire rounds like the lefh.
If you would want the behavior to be more like that of an artillery, keep the projectile_ext and only change the launcher_marker. Weapon\tracking\normal\max_up will also have to be changed to the maximum limit the blueprint can use. Check in world builder to see what it is.