Though Bulgarian participation in WW2 was very limited compared to other axis nations, they did design a few interesting weapons I think are worth taking a look at. All of these weapons are prototypes and should never be added to a techtree, data on these guns is inconclusive and sparse.
Spasov M1944 Tri-gun
Currently housed within the Sophia Military Museum, this unique weapon shoots at 3,000 rpm from three barrels (I assume 1,000 rpm from each barrel). It has three 30 round magazines.
Spasov M1944
Single barrel variant.
Spasov M1939
Earlier Spasov prototype submachine gun.
Spasov M1938 LMG
Visible in the pictures of the Spasov M1944 Tri-gun.
Bojinov “BIC” M1944
This pistol carbine was likely based on the luger.
“MUD” Pistol
Another Bulgarian luger attempt, possibly also designed by Spasov.
Here is video someone took at the Sophia Military Museum showing off some of the guns.