Translator notes:
 

Dear PC Martel,

Farsi  is what we call the Persian language, and it is written in the same characters
as Arabic, though it is a distinct language of its own, unlike the Arabic spoken
throughout the Middle East and North Africa, which differ only because of dialect
changes.  Arabic ,Hebrew, Aramaic (Syriac) are all written right to left.
The end result is that the three panels are separate and the conclusion
of my translation is that they are combined to read:

 "I am fighting for the sake of god and my faith and with his help I can defeat my enemies"

The year 1199 A.H.  coverts to the year 1784 AD  and the conversion table that was used
is located at the following link:  http://www.ori.unizh.ch/hegira.html
 

Sincerely,  Shimon Joffe
 

Right panel on flintlock barrel

Translates to:  "God is directing to (to face) between those who are not working (collaborating) and the enemies against him"

Top panel on flintlock barrel

Translates to:  "Year 1199, God is giving the tax to die for  his sake"


 

Left panel on flintlock barrel

Translates to:  "hand in hand, him and you and us and to be led rewards the face of god"

Three panels combined to read:

    Year 1784   "I am fighting for the sake of god and my faith and with his help I can defeat my enemies"
 
 

Next five images are the left panel from left to right.

Next four images are the top panel from left to right.

Next four images are the right panel from left to right.

Last image is of design or writing on tag area of barrel