I have these 2 M4 style barrels that have non standard chambers. Does anyone recognize theses markings. They are definitely not 7.62x39 or 5.56. Attached File

That longer chamber area, are they AR-10 pattern or similar larger cartridge?  What's the bore diameter and the diameter of the RE area?

Can only guess that if 06 production, possibly 50 beowolf or 450.

maybe 5.45x39 from  the Alexander Arms Genghis M4

How big is the bore diameter?  That might be a good start.

Greg

What pistol shell will slide in the chambers? What is the size of the bore?
If the barrel has a locking extension see if a 5.56 or a 7.62 bolt fits if not locking then it is blow back
A 9mm would say 300BO or others
A 45 ACP would open up 45 super-450 bushmaster.
There are a few bigger than than a 45 ACP the 50 BW or 450 socom come to mind
You need to think about a chamber casting
FYI a simple chamber casting can be done with aluminum foil.
Stuff the chamber with a long strip of foil and make it tight. But don’t hammer it in
If it has a barrel extension try to lock a bolt into the extension to get a shell length to the aluminum foil plug
Push out the plug with a cleaning rod and measure