Tinkers is, without doubt, one of my favorite mods or even what I like most: either by the weapons or the modifiers and the powers you end up with. The most beautiful parts are undoubtedly the long range weapons and to these I think it may make sense to add more modifiers.

Arrows and Darts. Arches and Crossbows

Punch Through

There are elements that can make projectiles travel instantly but do not trespass mobs, which is bad because if that happened it was completely fantastic. When we talk about this seems to be too powerful but it is supposed to be an end game weapon and even so not all monsters can have this: bosses should not trespass.
In addition to this they can have the damage can be reduced by each mob that passes. If you still think this is too OP then play with Scaling Health

Multi-shot

And what about adding some kind of glass or even a mirror that copies the projectile and that throw together with the main projectile another set of x (+1 for each added spit). Each projectile gives 50% of main damage but copies all statuses and has 80% accuracy versus main.

It's supposed to be an early game thing but not too easy to get.

Craft Ideas: Bone meal + glass pane + GlowStone poder

Explosive projectiles

Play ONCE with this and the mod that adds the metal crashed or was discontinued and I never managed to do it again but is a fantastic idea!
It is the only modifier that spends durability even if it is unbreakable. It is added by adding a Flint and Steel and gunpowder. Such as Lapis Lazulis and RedStone, the amount of gunpowder will indicate the level and the Flint and Steel may: either lose durability by use or be even consumed. It has a 40% probability of exploding and a further 20% if the mob is on fire. adding more of this just increases the damage and / or range of the explosion.

Damage Range and Multiplier

For long range weapons we have the ability to reduce the firing time but we have no way to increase the range or multiplier damage! It's sad but you may have an idea for it.

To achieve it should be something that would make sense even for the shrikes and possibly other weapons if they develop for MC 1.13. However we may have a change in the effect of how the weapon is used.
Weapons that use throwing force do not have a damage multiplier so these two can be the same: Power Potion.

For the range of bows and crossbows can be increased by adding vanilla arches + slime balls as if the reach of these arches were added to the weapon in question.

To be clearer:

• Power Potion
  • shurikens → increase range
  • throwing weapons → increases reach
  • arcs → increases damage multiplier
  • Beasts → increases damage multiplier
• Bow + slime
  • shurikens → not applicable
  • Shooting weapons → not applicable
  • Arcs → increase range
  • crossbows → increase range