Did the cannon of the Bf-109 fire through just the prop-hub or through the engine?

Answer 1

first answer:

It shot though the entire engine. It's crazy, right? well it worked a little to good.

second answer:

With the Bf-109 (Me-109) any thought of having a cannon (15mm, 20mm or 30mm) firing through the Propeller Hub required an engine designed, from the start, with that in mind. The engine would have a hollow core that allowed the gun to be fitted inside (through) the engine and fire out the front through the propeller hub. The cannon's barrel would extend close to the prop hub.

Bf-109E series used the Daimler-Benz engines: DB-601A, DB-601N, and DB-601E. The DB-601A had space for a 20mm cannon, but it was not employed in operational fighters because of issues relating to over-heating. The DB-601N & DB-601E could have fitted the cannons in 'E' series, however in practice they were not used w/ prop guns in this particular series. Instead, the 'E' series models fitted two cannons inside the wings (one per wing), and not in the prop (although the propeller spinner was hollow). These two engines were used in the subsequent "F" series BF-109, and then one gun (either the 15.1mm or the 20mm cannon) were used to fire through the prop. In the 'F' series and later, the wings were not designed to handle cannons mounted inside. Cannons were only fitted to the wings in under-wing gondolas.

In the 'G' series the DB-605A and DB-605D engines were used. The DB-605A could use the 20mm fitted to fire through the propeller hub. The DB-605D could also handle the larger 30mm cannon firing through the hub.

Although the final 'K' series of the Bf-109 used the DB-605ASCM and DB-605DCM engines, it is not likely that the DB-605ASCM was able to handle the larger 30mm cannons, being that it was a variant of the DB-605A.