Yes they will fit under the helmet. However its going to cause pressure points on your skull and give you headaches after about 30 minutes. Im a recon marine and Ive worn multiple types of ear pro in a multitude of environments doing many different things. If youre going to wear muffs and a helmet, get a high cut and have the earpro attached to rails on the side of the helmet. Anyone that tells you comfort doesnt matter operationally is a fool.
Im also a recon marine, and I second the comfort is super important and to use a high cut helmet. Its 2019, the old michs are out of date
I am not a recon marine, but the design of the helmet was to allow some hearing but still offer protection to the side of the ear/temple. If you want to sacrifice possible protection for comfort, its up too you.
Yes helmet earpro hanger adapters work on this style of hangers which are on alot of different earpro