May have been stated already, but 22 LR out of a pistol is much louder than from a rifle from my experience. You can almost go w/o hearing protection with a rifle (not recommended). With a pistol, it will ring your ears.
Also, DB readings can depend a lot on how it was tested. How far away it was from the source.
I had a 5.45X39 round go off indoors a few feet away from my head once. My ears were ringing for a couple hours.
I haven't shot indoors in a while, but I got in the habit of doubling up on the protection when I did. I still do that for pistols if I can. 30 DB soft insert plugs plus decent muffs. I don't have electronic muffs. Need to fix that.
The only thing I would mention is be careful using muffs only. If they don't fit and seal right around your ears, you will not get the rated protection.