UZI Conversions - Full Size




The ATF opinion appears to be that you can do just about anything you want to a semi automatic UZI receiver to bring it up to SMG specifications except for one thing - removing the bolt blocking bar.

The Model A and Model B semi automatic UZI carbines all had a bolt blocking bar welded to the inside of the receiver. This bar prevents an unmodified SMG bolt from being used in the gun and was required by the ATF to get approval to sell the gun in the US. Removal of this bar is considered to be manufacturing a machinegun, and results in what is known as a "registered receiver". That is the preferred way to convert an UZI and permits the use of unmodified SMG bolts. Not all of the transferable registered receivers converted before 1986 had the blocking bar removed. Some people registered the receiver but used a slotted bolt with it. In those cases, the bolt was usually unmarked (since it was not the registered part) but it is "married" to the receiver because separating it from the receiver would create an unregistered machinegun. Because of that, a registered receiver that still has the block bar attached is no more versatile than a registered bolt. Since May of 1986, only class II dealers can create a new machinegun by removing the blocking bar and the gun is considered to be a dealer sample, not transferable to individuals.


Instead of removing the blocking bar, many people created a registered bolt by taking a standard SMG open bolt and milling a slot on the side so it could pass over the block bar. For people doing transferable conversions before 1986, doing a registered bolt was convenient because they could get a large supply of bolts and the conversion process was easy. B&G is probably the most common registered bolt around today. Here's a picture of a registered B&G bolt. The vast majority of registered bolts are open bolts, but there are a few registered closed bolts. They were usually made by taking a semi automatic closed bolt and welding up the lower lip so they'd run properly as a full auto. The welded up lower lip is not as durable as an original factory bolt.





It has been reported that some of the early semi automatic Model A carbine's that came into the US had a fully supported bolt face. Representatives from IMI have denied it and the ATF probably wouldn't have allowed it, but it's possible that IMI forgot to mill off the lower lip on some of the bolts or the ATF didn't initially realize that it was an issue. It's also possible that IMI made these bolts available separate from the guns for conversion purposes. Regardless of how they got here, original slotted IMI closed bolts with a lower lip do exist but they are quite rare. They would have been an ideal bolt to register prior to 1986, requiring no modifications to the receiver or the bolt.



Depending on what type of bolt was used in the conversion, there may or may not be a conflict with the barrel restrictor ring. For information on the barrel restrictor ring, see the main conversion page. How the restrictor ring is handled in the conversion will determine what kind of barrel can be used in the gun. Another thing affecting the barrel is the trunion. The inside diameter of the threaded end of the trunion is smaller on a semi automatic UZI carbine than it is on an SMG. This prevents SMG barrels from being inserted into an unmodified semi automatic trunion. A full conversion should bore out the trunion to SMG specs, although it usually was not done. If it has not been done, then the forward trunion band on an SMG barrel has to be turned down to use it in the gun. Here are some different barrel configurations that could be needed in different types of conversions:

  1. Factory IMI Chrome lined SMG barrel. Note that the SMG barrel has the larger diameter band after the flange and thus requires the trunion to be opened up to SMG specs. This barrel also has the full barrel diameter all the way to the chamber end, requiring the barrel restrictor ring to be removed.
  2. An original SMG barrel that has the front band turned down to fit in a semi automatic trunion and the chamber areas turned down to fit in the barrel restrictor ring. This is commonly found on conversion guns, especially if spare barrels are desired.
  3. Chrome lined Bushmaster barrel. The front band and chamber are smaller diameter for use in an unmodified semi automatic receiver, plus the secondary band is in place for additional trunion support. This gives the barrel three areas of support - the restrictor ring, plus the rear and front of the trunion.
  4. Chrome lined barrel that appears to be an original IMI semi automatic barrel cut down to SMG length for a registered conversion or an SBR. Note that there is no secondary trunion band so support would be by the front of the trunion and barrel restrictor ring like a normal semi automatic barrel.

When transferable conversions were being done in the 1980's, surplus UZI parts were harder to come by and more expensive than they are today, so there was more incentive to convert existing semi parts then to replace them with SMG parts.


Conversions could also be done via registered sears. Fleming removed the bolt blocking rail from the receiver and engraved his information on the bottom of the receiver as seen in the picture below. The sear was also crudely engraved with the same info with a vibrating pencil engraver. These sears are permanently married to the receiver and cannot be removed. While this information may not be documented on the current form the gun is on, it should be. Qualified did some registered sears that are not married to the receiver but are extremely rare.



Receiver Markings:
As a final touch, people doing conversions may have restamped the receiver markings to make the gun look like an original SMG. Most conversions were not remarked. Fleming did a "Basic" and "Deluxe" UZI conversion. The Deluxe consisted of remarking the receiver to say "UZI SMG" (although a factory IMI UZI should really be marked "SMG UZI"). The Deluxe also had the lower remarked to ARS while the Basic was usually AFS.

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