What is the protection rating for these with gunfire?

I don't know the actual rating per se but I have used these with shotgun, pistol and AR15 with no issues of bleed through whatsoever. They functioned flawlessly every time. In between lulls toy can hear range commands clearly and can carry on regular conversations without having to shout.

What is the main difference between these and the Custom Molded Earplugs?

Totally different. Custom molded plugs go deeper into the ear canal past the second bend. The Decibullz are only molded to the outside of the ear or bowl. The greatest protection is when it’s molded to the aperture, or opening, through the second bend. Custom molded plugs can be made with a filter which blocks noises over 85dB but allows softer sounds in, such as conversation. Cost is about the same. Trust me, get custom molded plugs.

They allow me to ear voices (colleagues) and block noises in marine engine room? Not blast, is a constant noises

Our Percussive Filters are designed to block out sudden loud percussive noises such as an explosion or gunshot. If you are looking for consistent noise reduction I would recommend checking out our regular Custom Molded Earplugs https://www.amazon.com/Decibullz-Earplugs-Comfortable-Protection-Shooting/dp/B00WIXL6IM/ref=sr_1_2?ie=UTF8&qid=1494436138&sr=8-2&keywords=decibullz. If you have any other questions please feel free to contact us at support@decibullz.com.

Thanks for reaching out. The new percussion filters are designed to block out loud percussive noises while still allowing ambient noise to pass through. When a loud percussive noise is not present the earplugs will have an NRR of around 10. As soon as a gun blast or any other loud percussive noise goes off, the filter will close bringing the NRR up to as high as 33.