Carbine assist springs
 

Would someone explain how a carbine assist spring works? I assume the help the toggle assembly action close? Or open?

You are correct that it helps close the action after firing. The leaf mainspring is not sufficiently strong enough to return the heavy receiver group, barrel and forestock back into battery by itself.

assist spring
 

Hi Major Tom, The 1902 carbine was basically a 1900 .30 cal. with the addition of a longer, heavier, barrel, a forearm, and finally a shoulder stock. Much like an artillery, but in .30 cal. The flat bi-leaf main spring works fine on a 1900 with a pencil thin barrel, but pooches out when faced with the added weight of the carbine barrel. In order to move that much additional mass thru all the necessary cycles, it, the main spring, has to be light enough to allow full recoil, but, still remain strong enough to close the action completely on a loaded round! The early lugers are seriously weak in this regard. So, the Luger engineers added a small coil spring in the forearm and a small lug on the bottom of the barrel, to add just a skoosh more spring to the whole affair, hopefully to help cancel out the additional mass of the barrel and to assist the already weak closing issues mentioned earlier... Now, this obviously didn't cure up the problem to enjoy any kind of dependability, so the engineers also came up with a high pressure round just for the 1902 carbine to get all the energy required to finish the job... I don't reload, so I'm stuck with PPU .30 Luger ammo as being the best horse for the race... But in the case of the carbine, it's like cutting off one of his legs?... Anyway, the assist springs power, or compression strength or weight is limited by the little fixture it fits into?... so the balancing act is weak enough to open/full function, and strong enough to close, plus snotty enough to do all of the above?.... If anyone can help, with spring data, or loading info, it would be appreciated... :cheers: best to all, til...lat'r....GT...:cheers:

Some time ago someone wanted the dimensions of the carbine forearm assist mechanism, so I made up some photos. Here are a couple I have on file that will give folks who are unfamiliar with the Luger carbine a little idea of what we are discussing.
Ron

Just to make it clear, the auxillary spring also has to be overcome to "open" the toggle,
this is probably why the carbine ammo was loaded "stronger".

More spring pressure from the Aux. spring was needed to reliably close the toggle, which required
"stronger" ammo to open the toggle and achieve full recoil(and thus allow the hold open function). JMHO. :)

The Aux. spring works in conjunction with the mainspring to cycle the action, a much stronger mainspring would have sufficed, but engineering limitations of space and flat springs struck the engineers! ;)

The carbine with coil spring can be made to work without the aux. spring, even with a forearm.

Thank you gentlemen for the excellent explanation.

Very much appreciated Ron ... Thank you