The accelerator was added not to aid the function of the bolt, but assist in returning the heavy barrel/receiver/forearm to its forward position. The mainspring was sufficient to return the bolt to battery.
To get back to the former discussion: Everyone has gotten so hung up on the â??needâ? for +P ammo to make a 9mm carbine work they have missed an opportunity to have another â??blinding flash of the bleedin' obviousâ?. Do let us talk about the â??physicsâ? involved.
(I need to interject a note here: I found my copy of the 1904 DWM munitions catalog. Both the 471A and 480D cartridges are listed for the carbine, both are indicated to have a blackened case, and there is no mention of the 480D not being offered for sale.) The 471A cartridge was developed for the carbine to make it function properly. The projectile for the regular 471 7.65mm cartridge was exactly the same one used in the 471A. So given that the energy imparted to recoil and operating the action is directly proportional to the mass and velocity, since the masses are equal the energy was upped by increasing the velocity, i.e. the 471A was loaded hotter (but this we already knew).
Now, just for the sake of discussion, let us assume that the velocity of the 7.65mm and 9mm cartridges are the same (in modern loads they are fairly close 1200 ft/sec vs. 1150 ft/sec respectively). According to the 1904 catalog, the weight of a 9mm projectile was 8 grams and the 7.65mm was 6 grams. The 9mm is 33% heavier than the 7.65mm! Since energy is the direct product of mass and velocity, for the same velocity the 9mm also has 33% more energy. It has much more â??uumphâ?, i.e. it is inherently a hotter round.
How much hotter? Consider the mechanical difference between a 1900 7.65mm Luger and a 1902 9mm Luger. Basically they are the same. Sure the â??02 is a larger caliber and has a fatter barrel, but there is one more profound difference. To accommodate the hotter 9mm round, the mainspring was beefed up. The flat mainspring consists of two laminations. For the 7.65mm both laminations are the same thickness (this also applies to the carbine). But on the 9mm, the forward lamination is roughly 50% thicker than the rear lamination to absorb the extra energy of the 9mm. See the following illustration:
So, the extra energy of the 9mm is already the equivalent of a +P 7.65mm round. I havenâ??t been able to find the performance figures for the 471A cartridge (the +P for the 7.65mm if you will) but I would be very surprised if the muzzle energy of the 471A isnâ??t real close to the 9mm standard round.
â??The simple fact that the 9MM Parabellum cartridge lacks the kinetic energy to reliably cycle a carbine actionâ?â?¦sez who! With the same mainspring in the carbine as the 7.65mm version (i.e. not beefed up), the 9mm would have the necessary increased â??uumphâ? to cycle the carbine action. This probably became apparent early on which might account for the 480D cartridge being dropped from the market between 1904 and 1913â?¦it wasnâ??t needed!