Note the spacer bushing that was made to make up the difference of the length of the striker (between the back of the bolt and front of the striker spring).
The recoil spring, by the way was pretty weak compared to other open bolt SMG springs. In the actual testing, the same recoil spring and striker that is shown with the closed bolt is used. For illustrative purposes, the open bolt is shown with the open bolt recoil spring assembly installed and a different striker spring over the recoil spring. Weight is negligible between open and closed bolt.īelow is the test setup.
In FA, the open bolt and closed bolt function the same.ģ. The closed bolt assembly will not function without the buffer to properly guide the striker spring.Ģ. Without the buffer, the striker spring is not guided properly and will bind up.Ī test needed to be performed without the buffer to determine the striker springs affect on the ROF.ġ. You can see that there is just a little bit more distance left before the back end of the “feet” of the bolt would contact the front of the sear.Ģ. In the picture below, the bolt is positioned at the farthest point it can go until the striker assembly bottoms out on the buffer. In semi auto, the sear pops back up when the trigger is pulled. To prevent the bolt from going back too far which would hit the sear in semi auto operation. There are at least 2 reasons for the need of the “semi” auto buffer.ġ. While it is obvious that decreasing the bolt travel will definitely increase the ROF in the OPEN bolt UZI, in the case of the CLOSED bolt UZI, the buffer has very little if “any” impact on the ROF which will be demonstrated shortly. The closed bolt setup requires the use of the semi buffer. The closed bolt with the striker assembly is 1 lb 11 oz….3oz heavier.Īs you can see from the first photo. Its hard to see in this picture but it is an 8. Weight? No, the difference in weight is negligible.Īs seen in the picture below, this IMI 9mm OPEN bolt weighs 1 lb 8 oz. This requires that the striker spring to be strong enough to be right behind the bolt to detonate the primer. Since the striker is following the bolt in FA, the operating principle is identical to the OPEN bolt UZI in the FA mode. With the lip there, the lip strips the round from the mag and the firing pin doesn’t touch the round/primer until the cartridge is in the chamber. With the absence of the this “lip”, when a round is being stripped from the mag, the firing pin would already be protruding forward and then would get hung up on the rim of the case.
The FA closed bolt UZI needs the supporting lip as circled in the second picture from the top for proper FA functioning. There is nothing that the bolt “trips” in order to release the striker when the round is in battery. Unlike most other closed bolt SMG’s/MG’s, the UZI has no hammer. Installing the same spring in the closed bolt setup, you can see how the spring gets fully compressed. Using the recoil spring from the closed bolt configuration then installing in the open bolt, you can see that the guide rod can be shoved all the way in the bolt without the springs becoming fully compressed. The picture below shows a depth of 3.929″ for the CLOSED bolt The picture below shows a depth of 5.5435″ for this IMI 9mm OPEN bolt
Uzi semi firing pin assembly full#
In addition, the closed bolts (semi and full auto) do not have the recoil spring hole counterbored as deep as in the open bolts.
Uzi semi firing pin assembly full size#
Notice how the full size UZI closed bolts have a much smaller ejection port than the SMG bolt. Notice that the semi bolt is slotted for the bolt blocking rail and has no supporting lip at the breech.įinally a side view. This is a common question that this article hopes to address.īelow is a picture of an IMI full auto closed bolt assembly for the full size UZI – this is a 9mm boltīelow is a comparison of three UZI bolts. Why does the closed bolt full auto UZI shoot so fast?
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