B&T VP9 Suppressed 9mm Welrod Pistol and Mauser Model 98

Sound reduction: the B&T VP9 / Welrod-style integrally suppressed 9mm pistol is dramatically quieter at close range (designed to be “very quiet”; some historic Welrod tests measured levels that are low enough to be described as “vacuum-cleaner quiet” in practical terms). A .30-06 Mauser, even with a modern rifle suppressor, starts much louder because the cartridge produces a large muzzle blast and (unless you use subsonic ammo) an unavoidable supersonic sonic crack. Suppressors on rifles typically reduce peak muzzle blast by ~20–35 dB, but cannot eliminate the bullet’s sonic crack for supersonic loads — so a suppressed .30-06 will still be clearly audible at distance and usually louder than a Welrod/VP9 firing subsonic 9mm.
Accuracy: the Mauser Model 98 bolt-action rifle with a proper scope and good .30-06 ammunition is far more accurate at long range than any pistol. A military Mauser can be made (or tuned) to deliver 1–2 MOA or better with the right barrel, bedding, and ammo — practical accurate hits out to several hundred yards are routine. By contrast, a Welrod/VP9 style bolt-action suppressed pistol is intended for very short-range, deliberate shots (historically described as accurate to ~15–30 yards and best used in contact); it’s not a long-range precision tool. In short: rifle >>> pistol for accuracy/long range.

Muzzle blast energy: a .30-06 burns a lot more powder and vents a lot more high-pressure gas at the muzzle than a 9mm; that makes the initial blast much louder. Suppressors slow and cool those gases and can reduce the blast substantially (commonly 20–35 dB), but suppression can’t hide the energy entirely.
Sonic crack: bullets traveling faster than ~1,100 ft/s produce a sonic boom (“crack”) along their flight. A suppressor can’t remove that; only using subsonic ammo (bullet < sound speed) avoids it. Welrod designs use ported barrels and subsonic loads to ensure the projectile is subsonic and the gas is vented into the suppressor, which is why they’re so quiet at the muzzle.
Action noise: bolt-action pistols like the Welrod/VP9 minimize action/noise because they’re manually cycled; semi-autos add mechanical noise. A Mauser bolt has low action noise, but the rifle’s muzzle signature dominates the sound picture.

Unsuppressed .30-06: ~158–164 dB (varies with barrel length and load).
Suppressed .30-06: often still in the 125–140 dB range for peak sounds (depends heavily on suppressor and whether ammo is supersonic or subsonic). The sonic crack will usually remain audible on supersonic loads. PrecisionRifleBlog.com+1
Welrod / integrally suppressed 9mm (historical tests / modern VP9): very low muzzle report at close range — historical Welrod testing and modern writeups describe very large reductions (Welrod tests and refurbished examples were described as “Hollywood quiet” or comparable to household noise levels at short range). Exact dB figures vary with measurement method; practical experience and tests show these designs are noticeably quieter than typical suppressed rifle shots.

If your priority is stealthy, close-range quiet, an integrally suppressed bolt-action pistol in 9mm with subsonic loads (Welrod/VP9 style) is much quieter than firing a .30-06 Mauser, suppressed or not.
If your priority is long-range accuracy and stopping power, the Mauser .30-06 with a quality scope is the correct choice — it will shoot rings around any pistol at distance, but it will not be as quiet even with a good suppressor (unless you deliberately use subsonic .30-06 loads, which greatly reduce velocity/energy and aren’t a common high-performance option).
Hearing protection is still recommended with any suppressor-equipped rifle — suppressed guns can still produce levels that damage hearing

difference between B&T VP9 Suppressed 9mm Welrod Pistol and mauser model 98, a .30-06 caliber bolt action rifle with mounted scope interms of sound reduction and accurracy.