I mainly use 1 1/8oz loads for pigeon hunts, but 7/8 oz-1oz loads work as well. Type of ammo also makes a difference in my guns. I have no issues with winchester or federal 1oz loads, but I recently went through a flat of Challenger 1 oz loads and there was the occasional fail to eject. Those challenger loads are pretty crap...I had issues with them in a Beretta and a Browning. One of my 48's seems to like high brass shells better then the cheap low aluminum shells, but that gun has probably 70000 rounds through it, so I forgive her for being a bit of a picky shell eater.
As for finding out the date, you cant do it by serial number, you need to find the date stamp. The date stamp should be at the bottom of the receiver near all the proof stamps and serial number stamp. You will also notice that the serial number on the barrel isnt the same as whats on the gun....and nor is the date stamp. I guess the barrels were made at different times then the receivers were, and as such the barrels are stamped with a different serial number and may have been manufactured in any year before or after the receiver was made. If the receiver has a date stamp, thats considered the date of manufacture. Some earlier Franchi's didnt have date stamps on the receiver, so you need to refer to the stamp on the barrel.
Date codes using roman numberals are as follows;
I - 1945
II - 1946
III - 1947
IV - 1948
V - 1949
VI - 1950
VII - 1951
VIII - 1952
IX - 1953
X - 1954
XI - 1955
XII - 1956
XIII - 1957
XIV - 1958
XV - 1959
XVI - 1960
XVII - 1961
XVIII - 1962
XIX - 1963
XX - 1964
XXI - 1965
XXII - 1966
XXIII - 1967
XXIV - 1968
XXV - 1969
XXVI - 1970
XXVII - 1971
XXVIII - 1972
XXIX - 1973
### - 1974