“The design of the 1927 Tokyo Arsenal submachine gun (試製自働短銃 1927年型) was created on the basis of small automatic weapons already familiar and mastered in the production.”
“Automation was used based on a short barrel stroke like the Nambu pistols of 1925, locking with a rising wedge, supply of ammunition from short metal cassettes similar to a Type 3 heavy machine gun (10 charging cassettes of 5 pieces each were combined into a belt and placed in a box).”
As you can see the weapon was fed by a belt stored in the drum, adding this feature and correcting the position of the bolt handle will greatly increase the enjoyment of using the weapon. It also would be greatly appreciated if you change the sound to this Sig MKPS from real life, the fire rate is 1350 RPM which is only 30 off from the Tokyo Arsenal SMG in game.
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Source for Tokyo Arsenal SMG: