HOW TO ADD A NEW AMMUNITION TYPE:
This is pretty easy. The system uses 3 things: An ammunition type, an object modification, and a keyword that's used to tie them all together.

Here's a step-by-step guide. The guide assumes you have Fallout 4 Edit (FO4Edit) installed and have some level of familiarity with modding.

Step 1: Set Up Forms
First, set up the ammo/keyword/OMOD. It's easiest to copy existing content; copy-as-new-form a an OMOD, ammo and keyword for an existing ammo type like 10mm AP.

Now you need to set up the modification used to apply the effects of the new ammunition type. It needs to add the keyword you set up in step 1, and switch the ammunition type to the one you set up in step 2. You'll also need to set up the 'NPC Ammo List'- this is the list that an NPC will spawn with if they spawn with a gun switched to this ammo type. The main file currently isn't set up for this, but yours should be. Then just set up the enchantments/recoil/damage modifications or what have you.

You can have multiple different mods using the same ammunition type, but each must have a unique keyword.

Be cautious about adding a 'Set: Projectile' entry- for many weapons, other mods set the projectile. Ballistic weapon silencers change the projectile, for example- if you change the projectile, you will break the silencer. Flamer mods change the spray length by changing the projectile. The plasma gun flamer barrel changes the projectile (as do all the other barrels!). Missile launcher tracking missiles also change the projectile- that's why Tracking Missiles are technically a different calibre.

Step 4: Set Up Lists
Finally, you need to register the ammo types with the lists Loads of Ammo uses. First, 'Copy as Override' the formlist for your ammo type's calibre (e.g. 10mm) into your new file, along with the lists a0aLOADS_FLST_Lookup_Equip_AMMO, a0aLOADS_FLST_Lookup_Equip_Keyword and a0aLOADS_FLST_Lookup_Equip_OMOD.

Step 5: Add to Lists