Big-Bang Model 12F

It is not known for sure when the 11F was replaced by the 12F. A distinct cut-off is right out of the question as Conestoga is known to mix old parts on new models to use up stock on hand. 12Fs were first advertised in 1924 and were produced until 1935 when the charger models came out.
All Iron 12F
Die-cast 12F

Above left is an all-iron 12F. On the right is the version with the 2-piece die-cast barrel, mistakenly referred to as the 12FR. A 12F noise reduction model has not yet been observed. (See 8FR)

The two different barrels are easily identified. Most noticable are the fins inside the muzzle on the die-cast version.
On the left is the iron version (some had pins to block projectiles, some didn't). On the right is the die-cast version with fins intended to prohibit discharging ordnance!
There is a big difference in the water sumps. The iron barrel (left) has the traditional square sump, while the die-cast has a "U" shaped water sump.
From the side, it is not easy to spot the difference, but you can do it. Notice the raised bands near the breech end on the barrel that is to the rear? That is the die-cast one.
Here is a collector's dream. Shown are four of six die-cast 12F's that were found in storage in 1998. Only one has been opened. The others may still have Wily's fingerprints on them!

The original shipping carton is falling apart, but the date is still legible; 6-26-24.