I suggest that the costs for this feature are reconsidered as it is an exploit right now. Right now it feels like a "1 free heavy artillery every turn" option.
In my first Russian game I dismantled a fort battery every turn until I had 10 or so and did not know what to do with them, I am sure the Austrians and Germans don't have that many together, on both fronts. In fact the only limiting factor is the number of forts, Russia has ca 20 I think.
Right now the event costs: 1 EP, 1 NM, 200 victory points. None of this really matters. The EP do not hurt, VP is uninteresting imo, and -1 NM easily balances out with a single won battle. The new battery is available instantaneously in the next turn at practically no cost.
Now, had I built 10 heavy batteries via the recruitment mode the total cost would habe been money: 1300, conscripts: 80, war material: 2500 and 60 days each. In the special case of Russia this would be their entire war material budget of 3 years! The conlusion must be that every Russia player absolutely must use the Unlock Fort Guns every turn until all his 20 or so forts are used up.
What I suggest is rethinking the cost, logical would be (to me):
NM: no loss (why would this be detrimental to morale? It could as well argued that it increases morale if the army gets heavy artillery). Leave this at zero
EP whatever
VP whatever
WM there should be a cost in WM, for example ca 1/3 of the normal cost, 75WM, to mobilize the guns (unless you just want them torn from their socket and put on a oxcart)
Money like WM, the event should not come for free and cost a certain fraction of the normal guns
Time not sure, it's ok that the unit is available rather quickly
By the way, does the AI make use of this event? The only way to balance it would be the AI using it (roughly) as many times as the player does.