It is not as loud as a .357 magnum, but it is loud. Even a .22 LR will hurt your ears, and do permanent damage.
When the .327 was introduced back in 2007, I did some tests, comparing the noise to a .357 magnum, and posted this in the review:
"With all of the negative comments early on from folks who have never fired the cartridge, there was a few things that I particularly wanted to test; those being muzzle blast, recoil, and penetration. I compared the muzzle blast of the .327 Federal Magnum to the .357 Magnum fired from guns with equal length barrels. I used for this test two Ruger SP101 revolvers, identical except for the cartridge. Holding the decibel meter beside the shooter’s head, the readings seem close, with the .327 registering 120db and the .357 reading 124db. However, decibel readings are logarithmic instead of linear, and 124db is noticeably louder than a reading of 120db. The .327 Federal Magnum does indeed have less muzzle blast than does the .357 Magnum, at least using factory loads with the same bullets weights. "
Now, the heavier bullet loads are not as loud as the factory AE 100 grain, but still loud enough the ear protection is a good idea.