The headstamp on this cartridge looks perfectly o.k. for Bulgarian. The “1” is the same as on most of my rounds. The “0” is identical, very narrow and straight-sided, not just a circle. the “5” is identical to that on my Tokarev rounds. the only point of departure is that on my Tokarev rounds the “3” is not flat-topped like on this Mosin cartridge. There is no particular reason that I am aware of why a 7.62 x 54R round has to have a raised headstamp. The fact that many countries seem to make it that way on this particular caliber doesn’t mean that Bulgaria couldn’t get smart and use a less complex (I would imagine) bunter-making process to directly stamp the heads of these cartridges.
The bullet is the funny part, not the headstamp. I agree that it looks like the shape of a German s.S. ball projectile, and perhaps even the sharper type P.m.K. ogive. It is not a shape I normally would associate with the 7.,62 Russian rimmed round, but then, while I have had hundreds of them go through my hands, and used to shoot a very minty Polish Mosin-Nagant M44-type carbine, I have never collected this round and am no expert on them, and fraqnkly, have never paid a whole lot of attention to minor points regarding them, such as ogive.
I see that John Munnery brought these to a European show. That guarantees their Bulgarian heritage. John is a knowledgeable collector living in Bulgaria. For dummies, they used odd components as they had them, or if they were cheap to make. I have a Bulgarian 9mm P dummy with a wood bullet and on a WWI-vintage Spandau case. I have a couple more with the same wood bullet on much, much later Bulgarian cases, indicating to me it was not uniquely an early Bulgarian type (Bulgaria did have 9mm Luger pistols in the WWI era, along with those in 7.65 Luger caliber). There are 7.9 x 57 Bulgarian dummies with wood bullets also, made on salvaged fired cases of about any headstamp.
Again, I admit the bullet is odd, but see no reason at all for questioning the Bulgarian heritage of this round. As to it being an original dummy cartridge, I cannot say, but if it came from JM, (not this JM - John Munnery) it almost certainly is.