I have the same model with the black receiver. Mine is proof marked RG. It is my understanding that Renato Gamba made both the Mauser 71 and Mauser 72E shotguns. (We call these Mauser-Bauer guns because that is how they are marked. Bauer in Warren Michigan was the US distributor for Mauser firearms at this time and the guns are marked Mauser-Bauer.)
Gamba Armi may have made the gun above.
My understanding of Gamba guns*:
Side by side guns: 1960-1988 Fratelli Gamba, Gamba Armi and Renato Gamba side by side guns were made by the firm of Zanotti. In approximately 1988-1990 Renato Gamba buys out the right to produce Zanotti side by side shotguns.
Prior to 1959-1960, Guissepe Gamba proof mark encountered (Guiseppe passes away leaving the firm to his sons Guido and Renato in ~1959-1960)
Over under guns:
~1960-1969 Fratelli Gamba marking on Gamba O/U guns.
1970 onward- Guns are encountered marked both Gamba Armi and Renato Gamba. The firm of F'lli Gamba becomes Gamba Armi about 1969-1970. Gamba Armi continues to be owned by Guido and Renato Gamba. The Firm of Renato Gamba is owned by Renato Gamba only (??). There is still mutual cooperation going on between the two firms. The exact nature of the cooperation no one outside the family understands completely. Gamba Armi employed about 250 employees in the factory and another 200 finishers and engravers outside. It appears that at this time Gamba Armi was one of the largest shotgun producers in Gardone V.T. (if not the largest). Gamba Armi appears to have only produced guns on their own receivers.
The firm of Renato Gamba was much smaller perhaps a dozen employees? Renato Gamba appears to have produced guns for Mauser and Mannlicher as well as their own brand. Renato Gamba models appear to utilize guild (what we would call "to the trade" in the USA) receivers from Gamba Armi, Angelo Zoli, Franchi, Armi Techniche (Emilio Rizzini) and others.
Gamba Armi continues to make model 610, 620 guns.
1972- Gamba Armi begins production of Rottweil M72 in 1972. Some 620 guns are encountered marked RG though. Apparently some Rottweil M72 guns are encountered that are proof marked Renato Gamba as well. Rottweil M72 is produced until 1986-1988 when the model is discontinued by Rottweil. The Model 72 is made only for Rottweil. (In approximately 1992 Rottweil introduces the Rottweil Paragon model made in Germany by the company that would be renamed "Krico" in 1996.)
1981- Gamba Armi begins production of the improved Model 81 guns as a Gamba Armi model. The Gamba Model 81 is mechanically identical to the Rottweil M72. Externally the Model 81 has scalloped side to the receiver and Gamba Army also produces the M81 in a deluxe model with false sideplates. The Gamba Armi Model 81 is produced until 1988.
In 1988 Gamba Armi introduces the Model SR88 Daytona. Both Gamba Armi and the firm of Renato Gamba produce the Model 88 from 1988-1990.
1990-1991 Renato Gamba buys out the intellectual property rights on the model 88. Gamba Armi ceases full scale production and Guido Gamba goes into the used machine tool business full time.
I hope this helps.
* The above synopsis is based on personal visits that I had in a visit to Gardone in August 2012. Two days I visited with Guido and Tomaso Gamba (Tomaso is son of Guido). I bought some parts for Gamba Armi models at Gamba Armi. Two days later I had a separate visit with Renato Gamba and Carlo Gamba (Carlo is son of Renato and now President of BREMEC, SRL) regarding the Daytona Model and repair parts for Renato Gamba arms.
The synopsis is also based on a collection of Fratelli Gamba, Gamba Armi and Renato Gamba Company catalogs that I have put together over the years. I have also put together a catolog of photos from gun listings on Gunbroker, Auction Arms, Gun List, Rock Island Auction etc.
I also have 9 Gamba guns in my reference collection. I have examples of Gamba 620, Konrad Wirnhier 67 marked 'Made Especially for Harry A. Willsie' (620 trap variant sold by Konrad Wirnhier at his school in Alaska), Rottweil M72 AAT, Mauser-Bauer Model 71 (x2), Mauser Bauer Model 72E (x2 1 trap, 1 skeet), Renato Gamba Edinburgh (Franchi 451/2003 SBT receiver), Renato Gamba Mannlicher Edinburg (E. Rizzini ?? SBT receiver), High Grade Renato Gamba Daytona 1991 Model Pigeon/ Heavy Game Gun, non-SST, 30" F/F (custom engraved receiver inlaid gold dragons in inlaid silver clouds in panels with excelsior grade scroll surrounding, Grade 4 Eng/Circ Walnut wood) photo of this gun here http://www.rockislandauction.com/viewit ... 6/lid/1684
These phots do not do the gun justice. RIA uses too bright lights. Gun was dirty as received from RIA auction. Previous owner had covered the wood on the butt stock with a product like Old English furniture polish. Some of it had gotten on the edges of receiver and smeared across the cameo grip cap. A quick wipe with denatured alcohol cleaned this gun up and it is much prettier now.