Final Fantasy XIV Database - Ffxivpro.com

I do lots of weapon swaps: (probably overkill but I try to squeeze as much out as possible)

Excal/Duban at the start for doing D objective. Seraph > RLB > Flat > Savage > KoR.

After D (depending on DD) I swap to Burt/Svrista for kiting H. Overkill but damage doesn't matter and losing hate is the only possible issue.

After H its Reikiko/Duban (or Aegis) for doing CBA bosses.

Once down in F I swap to Burt/Aegis for kiting and leave that on through G and E.

Excal/Aegis for Aminon.

Tips: I banish2 C/G plus the mentioned JAs. Save SP1 incase you need to blow it for a bad bitzer. Tank G at 5.5 and have your teammates stand at max distance on the other side. If you are doing Naaks/Flans after Aminon save Sentinel after WC during Aminon for quick snap hate after the mobs are tagged. PLD can do respectable damage on Aminon don't sleep on your contribution.

I'm asking if the 300 DMG is counted in melee attacks

I don't know what everyone else is rambling about, but back to the question: as far as I know, additional stats on ranged weapons and ammo DO count for normal melee attacks and non-ranged WS, the same way the reverse also applies (melee weapons stats affect ranged attacks/ws, with some conditions, "Main Hand ONLY"). The damage rating on the ammo has zero effect on melee attacks or melee WS.

Examples:

Hauksbok Bullet's MAB+40 will indeed give the same MAB effect if you use Aeolian Edge, for example. The same applies to Hauksbok Arrow's +20% WSD for something like Savage Blade (which is kinda why Savage RNG is busted with TP Bonus bow). Bayeux Bullet's -50 Enmity applies to all attacks, not just ranged attacks, though you wouldn't shoot it anyways. You effectively have capped enmity reduction for any action. But the ammo's damage rating does not impact your melee damage in any way.

Even Molybdosis's Critical hit damage +10% affects Evisceration damage or normal melee attacks, for example, even though the stat is on a ranged weapon. I can't recall if something like Tauret works for Ranged attacks, though (these are reverse examples)

However, some examples don't always work, at least in reverse order. Naegling's attack bonus doesn't apply to ranged attacks. Tenzen HTBF's "TP Bonus" Bow doesn't work for melee WS. However, augmented "TP Bonus +" gear does work for every WS, but those are special exceptions because the augment is unique. I know you specifically asked about ammunition, but I'm mentioning weapons too since it's semi related.

Not being sarcastic, I'm just not sure how you can't tell this; the purpose of any STAT-boosting ammunition above like I mentioned is clearly intended for non-ranged WS or abilities like Aeolian Edge or Quick Draw etc, and NOT shooting (exception is QD), given by the fact that the item is Rare/Ex and costs a lot of Domain Invasion Points, or can only be used once every long cooldown. Ask yourself why would SE release ra/ex ammo that you can only carry one of, if the stat is only applied when the singular bullet is shot? You'd have to farm more points every time just for one WS (unless you Unlimited Shot). That wouldn't make any sense.

Anyways, as far as a "a definitive answer to whether an ammo piece for a ranged weapon's DMG and stats are counted into regular melee attacks and non-ranged WS attacks", the stats count for damage calculation, the bullet or ammo damage rating does not. That's how I understand it.

I'm asking if the 300 DMG is counted in melee attacks