From the NAA website:
"Cylinders
I am having difficulty resting the hammer blade in the safety slot on the cylinder; any suggestions?
1. Yes, it's a critically important feature of the gun, so PRACTICE.
First: Make sure the gun is unloaded.
Second: Make sure the gun is unloaded!
Third: Retract the hammer to the point that the cylinder spins freely (about half-way) and keep it retracted.
Fourth: Looking through the top/rear of the frame, locate any of the five milled safety slots (those notches on the cylinder between the chambers), and position any slot directly beneath the blade of the hammer (which is still retracted).
Fifth: While still retracting the hammer, depress the trigger (and keep it depressed) now allow the hammer to settle into the slot.
You can (should) confirm engagement of the hammer in the slot by attempting to rotate the cylinder; if it does rotate, the hammer was not engaged in the slot (repeat the process). Visually confirm, also, by examining the alignment of any chamber with the bore; if a bullet could physically pass from the chamber through the bore, the gun is not 'safe'. In other words, if a chamber is located at 12 o'clock, the gun is not 'safe'; in the 'safe' condition, the upper two chambers are at one and eleven o'clock. 99.9% of the failures are because the trigger was not kept fully depressed while the hammer was being lowered (Step 5). Once you get the hang of it, however, you'll find the process becomes surprisingly easy, quick and natural. "
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Absent the hammer snagging on something, you 'theoretically' shouldn't have a problem. It's most likely best to have gun in a pocket holster or a NAA custom carry holster grip.