On another forum there is a discussion about US recoilless rifles and their calibers. This is not my area of expertise, nor do I have any reference material that is helpful, but I am interested in figuring this out.
Apparently the M-27 RR from the ealry 1950’s is 105mm in caliber. It’s replacement, the M-40 from the 1960’s is 106mm in caliber. Information from various posters on this other forum, including quotes from Wikkipedia, claim that the 105mm ammunition can be fired in the 106mm, but not the other way around. Others have suggested that the 106mm is actually a 105mm but is called 106mm to avoid confusion.
Are you confused yet?
Does anyone have information to help sort this out?
Up to this time, I’d only heard of the 106mm RR…