It's possible there were plans for this weapon to have distinctive sounds to account for the "runelock" firing mechanism. I didn't include this in the description due to there being little evidence and is just speculation on my part as to why there might be a separate soundset linked to this weapon by default.
The soundset as it was implemented contained no firing sound and all the sound effects of the weapon hitting appear to be the unarmed hit sounds (eg. the bullet will hit with the sound of a fist).

To that affect I tried to put together a soundset that has the default arquebus sounds as well one of the magic activation sounds in an attempt to approximate what a magic assisted firing mechanism might sound like. The result is very subtle, to the point it will probably be pretty unnoticeable with all the other sounds in combat, but I thought it would be interesting to include none the less.

If you'd like to try this open the dragons_dowry_sound_fix.gamedatabundle file included with this mod in notepad and paste the following code over what's currently there and hit save:

{
    "GameDataObjects": [
    {
            "$type": "Game.GameData.WeaponAudioEventListGameData, Assembly-CSharp",
            "DebugName": "wpn_ab_item_blazing_fury",
            "ID": "16dcb3b6-6d7f-455d-b1ca-ec1594389032",
            "Components": [{
                    "$type": "Game.GameData.WeaponAudioEventListComponent, Assembly-CSharp",
                    "HitAudioEventList": [{
                            "ArmorMaterial": "None",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }, {
                            "ArmorMaterial": "Brigadine",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }, {
                            "ArmorMaterial": "Cloth",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }, {
                            "ArmorMaterial": "Leather",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }, {
                            "ArmorMaterial": "Hide",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }, {
                            "ArmorMaterial": "Mail",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }, {
                            "ArmorMaterial": "Padded",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }, {
                            "ArmorMaterial": "Plate",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }, {
                            "ArmorMaterial": "Scale",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }, {
                            "ArmorMaterial": "Flesh",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }, {
                            "ArmorMaterial": "Bone",
                            "HitAudioEvent": "imp_glb_pen_gun",
                            "IneffectiveHitAudioEvent": "imp_glb_nopen_gun"
                        }
                    ],
                    "CriticalHitAudioEvent": "wpn_glb_crit",
                    "MissAudioEvent": "",
                    "ParryAudioEvent": "",
                    "SwitchAudioEvent": "ui_wpn_gun_equip_switch",
                    "EquipAudioEvent": "ui_wpn_gun_equip",
                    "HolsterAudioEvent": "",
                    "ActivateAudioEvent": {
                        "AudioEvent": "ab_fire_proj_single_quick",
                        "Delay": 0.25
                    },
                    "ProjectileActiveAudioEvent": {
                        "AudioEvent": "wpn_glb_gun_2h_activate",
                        "Delay": 0,
                        "FadeTime": 0
                    },
                    "ApplyToSingleProjectile": "true"
                }, {
                    "$type": "Game.GameData.AudioEventListComponent, Assembly-CSharp",
                    "SoundBank": ""
                }
            ]
        }
    ]
}