Sounds like you may have an FN Model 1950 30-06 bolt rifle made for the Belgian Government.
After WWII the Belgians were developing a new semi-auto, the Model 1949.
However, as a "safety" in case it didn't work out, and to produce needed arms for use in Africa, they also built a standard type 98 Mauser rifle in 30-06.
After the war, the US gave European governments lots of surplus 30-06 ammo, so it made sense for them to make use of it in a bolt rifle.
The Model 1950 was the only military Mauser ever made in 30-06 as the original chambering. Some South American countries also used 30-06 Mauser's, but these were all conversions from another caliber.
The 1950 is marked with the Belgian kings mark on the receiver ring. There were two king's of Belgium during production, so there are two markings.
The one I remember was King Baudoin, and those rifles were marked with "ABL", which had something to do with the three languages used in Belgium.
These rifles were used both in Belgium and in the Belgian Congo.
The ones used in Belgium are typically in fairly good condition.
The ones used in the Congo are usually badly pitted below the wood and are in generally poor shape due to the environment in which they were used.
The rifle itself is an FN "Standard Model" 1924/30 rifle,
The "protrusions" on the receiver are the clip loading "ears". A stripper clip is inserted into the guides and the cartridges are pressed down into the receiver.
Dur to the length of the 30-06 cartridge, the rear face of the receiver ring has a semi-circular cut to allow the longer rounds to clear the receiver when stripper clip loading.
The Model 1950 was a high grade rifle and is one of the best quality of all the later Mauser rifles.
In good condition, and with matching numbers, these bring higher prices.
The poorer condition Congo rifles are worth much less.