Both are named zasleh for the selectionFireAnim in the turret's config and the model.cfg has zasleh defined as a section. Then one proxy is named muzzleflash1, and the other muzzleflash2 those two are defined as bones in class CfgSkeletons:

class CfgSkeletons
{
	class Default
	{
		isDiscrete = 1;
		skeletonInherit = "";
		skeletonBones[] = {};
	};
	class myWeapon: Default
	{
		skeletonInherit="Default";
		skeletonBones[]=
		{
			"muzzleFlash1","",
			"muzzleFlash2",""
		};
	};
};

Then both have an animation defined to rotate them at random:

	class zaslehROT
	{
		type="rotationZ";
		source="muzzleHMG_ROT";
		sourceAddress="loop";
		selection="muzzleFlash1";
		axis="";
		centerFirstVertex=1;
		minValue=0;
		maxValue=4;
		angle0="rad 0";
		angle1="rad 360";
	};
	class zaslehROT2: zaslehROT
	{
		selection="muzzleFlash2";
	};

The vehicle has a custom muzzle source based on the reload animation source. I suppose you could do the same on a weapon with source = reload; using hidevalue and unhidevalue. It works on vehicles with hidevalue = 1; but I think the reload source on vehicles runs backwards compared to what it does on weapons.