Floydster, It's been about 10 years since I participated in USPSA shooting in an indoor range, but this is how I did it. When the .45acp and 9mm guys were shooting, I usually just used the foam-cylinder earplugs. When the guys shooting .38 Super (hotted-up enough to make "major") showed up, I covered up my foam-plugged ears with the over-the-head muffs.
Most cylinder-shaped foam plugs have a decibel reduction rating (NRR) of 32 to 36 decibels when inserted properly. Most muffs have a NRR of 25 decibels. As for the plugs, that doesn't mean just rolled up and inserted 1/4 or 1/2 their length into the ear canal. If you look at this type of plug, you'll see that one end is kind'a shiny, and the other end is kind'a dull. To get the full Noise Reduction Rating (NRR) of this type of plug, you GENTLY roll the plug between your thumb and pointer finger until it is small enough to fit COMPLETELY into your ear canal, and you insert it dull end first. You insert it far enough into your ear canal so that it requires you to use your finger and thumbnail to pull it out once it has fully expanded; about 30-45 seconds. You will have to experiment a little. For many people, this will be a little uncomfortable. These are made for the depth of the average ear. If you absolutely can't take it, withdraw it A LITTLE. These, being foam, will fit to your ear. Also, over a short time, your ear will adapt a little to accomodate them. If you wear them less than 'fully inserted', you won't get anywhere near the full noise reduction rating.
For most of my life, I've worked in an extremely loud environment (with 32 to 35 NRR plugs)... shot 200,000 plus rounds of .45 ACP, and maybe 2000 rounds through various rifles, untold lawn-mowings, and 250,000 miles on motorcycles, and who knows how many concerts. If it's gonna be loud, I'm wearing hearing protection. My company tests our hearing annually, and I have lost some hearing in the conversational level in my left ear, but in nearly all other frequencies, I fall into the 0 to 5 decibel range; meaning that I can hear sounds beginning in the 0 to 5 decibel range. The lady that does our testing annually tells me that I have the hearing of a pre-teen.
I know that I have advised you to insert the foamies deeper than previous posters. Sorry Mejeepnut. I'm 50 years old and have a solid baseline regarding my hearing loss or lack thereof.
When you're shooting, use the good foam plugs, inserted as deep as you can handle (and still be able to withdraw them), and cover them with the over-the-ear muffs when you can. The NRR's add up (32 for the foam, and 25 for the muffs equalling 57). Also, something you should know.... every 6 or so increase (or decrease) in decibels equals an approximate doubling of sound volume. The increase is not linear, it's geometric. Example, sound A is 60 decibels (actually very quiet). Sound B is 66 Db. Sound B is not 10% louder than sound A, It's actually twice as loud.
If you're interested, and you must be or you wouldn't have asked about hearing protection, go to
http://en.wikipedia.org/wiki/Decibel
Thanks for listening.
Robb