Based on Browning's manufacture codes no serial number using an X was used until after 1976. The X stands for a 3. There is no code for an O nor is there a model for a Sweet 16 for 123. The Sweet 16 code for models made after 1976 is 121. Sweet 16's have not been manufactured since 1992.
It depends on the browning model of shotgun you are asking about,and the condition it is in.
I would like to start first with the serial number.The letters MR in the middle of the serial number indicates that your browning shotgun was made in 2007.With that said,if you have a pump shotgun then you have a browning BPS.If you have a over/under shotgun then you have a browning citori.If you have a semi-auto shotgun then you have a browning gold model.
No such model number.
This Shotgun was made by Stevens their model. 520. Made from 1930's to 1950'S Although the shotgun was Browning patent marked, it was not made by Browning.
If your over under shotgun was made prior to 1964,then the model of your Browning shotgun should be named the superposed.
I would need a more detailed description of your Browning shotgun including the model name or number,the overall condition of your shotgun,and the bore condition,along with the serial number(to date the manufacturing date) to give you the answer that you seek.
Browning never made a Model 51 shotgun.
You will have to call Browning and ask
You must call Browning to find out.
A5
The only model that Browning made that comes close to your question is the model B-80.These range in price from 230-300 dollars.As far as my research indicates,Browning never has produced a model 8 shotgun.
No such model name in the Browning line.