Externally, the TT-33 is very similar to John Browning's blowback operated FN Model 1903 automatic pistol, and internally it uses Browning's short recoil dropping-barrel system from the M1911 pistol. In other areas the TT-33 differs more from Browning's designs — it employs a much simpler hammer/sear assembly than the M1911, with an external hammer. This assembly is removable from the pistol as a modular unit and includes cartridge guides that provide reliable functioning. The Soviet engineers also added several other features such as locking lugs all around the barrel (not just on top), and made several alterations to make the mechanism easier to produce and maintain, notably a captive recoil spring secured to the guide rod which does not depend on the barrel bushing to hold it under tension. Production even machined the magazine feed lips into the receiver to prevent damage and misfeeds when a distorted magazine was loaded into the magazine well. The TT-33 is chambered for the 7.62×25mm Tokarev cartridge, which was itself based on the similar 7.63×25mm Mauser cartridge used in the Mauser C96 pistol. Able to withstand tremendous abuse, large numbers of the TT-33 were produced during World War II and well into the 1950s.The TT-33 omitted a safety catch other than the half cock notch which rendered the slide inoperable until the hammer was drawn back to full cock or pulled back to full cock and then lowered manually, which made it unsafe to carry when loaded. It also had a tendency for the magazine catch to accidentally release the magazine while drawing or firing the pistol, if the magazine was damaged in any way.