I use both sometimes but more importantly, use a device with a minimum of NRR 29, prefereably higher. I use NRR 33 plugs or NRR 33 muffs.
Gunshots register about 164 decibles (more indoors). The higher the NRR rating the less damaging wave enters the ear canal.
NIOSH recommends using subject fit data based on ANSI S12.6-1997 [or most current edition] to estimate hearing protector noise attenuation.
If subject fit data are not available, NIOSH recommends derating hearing protectors by a factor that corresponds to the available real-world data. Specifically, NIOSH recommends that the labeled NRRs be derated as follows:
Earmuffs - Subtract 25% from the manufacturer's labeled NRR
Formable earplugs - Subtract 50% from the manufacturer's labeled NRR
All other earplugs - Subtract 70% from the manufacturers labeled NRR
1. When the noise exposure level in dBC is known, the effective A-weighted noise level (ENL) is:
ENL [dB(A)] = Workplace noise level in dBC - derated NRR
2. When the noise exposure level in dB(A ) is known, the effective A-weighted noise level is:
ENL = Workplace noise level in dB(A) - (derated NRR -7)
There are other single number ratings available. For details refer to the Canadian Standard CSA Z94.2. Another single number rating is based on (Subject Fit) Real Ear Attenuation measurements, known as Single Number Rating (Subject Fit 84th percentile) and abbreviated as SNR (SF 84) (for details see ANSI Standard S12.6). "SF 84" indicates that 84% of the users in a well run hearing conservation program are expected to receive at least that much protection.