A Vector Arms Uzi in the Small Arms Research reference collection. Photo by Jeff W. Zimba
By David Gaboury
The UZI is known as a tough, tireless workhorse that never fails. While there’s a lot of truth to that, it needs good care like any other firearm. Out of spec parts or poor maintenance can quickly put your afternoon of fun on hold. Here are some suggestions to consider the next time your workhorse stumbles. Most of these suggestions apply to fully automatic or semiautomatic UZIs but you’ll find that replacement parts for the semiautomatic are harder to find and more expensive so there’s an incentive to repair rather than replace in that case. The three most common problems you’ll run into are failure to fire, failure to eject and failure to feed.
Failure to Fire
A failure to fire occurs when the round is fed into the chamber but the primer doesn’t detonate. Usually, the round will have a light primer strike on it. There are three possible causes for this. First, the open bolt firing pin, which is a small projection milled into the bolt face, may be worn or broken. This is an uncommon cause but if it happens, the firing pin will need to be welded up or the bolt replaced. Surplus bolts are cheap and plentiful so replacement is usually the easiest option. The firing pin on the semiautomatic UZI is pinned to the carrier and can also be replaced if worn.
Another cause is excess headspace. If the round doesn’t seat firmly in the chamber, the bolt will push the round forward rather than detonate the primer. Excess headspace can be caused by an out of spec chamber; but that’s uncommon. A more likely cause is a loose barrel nut. This simple to diagnose, simple to fix problem can easily go unnoticed. With the barrel nut tightened you should not feel any play in the barrel. If the problem is chronic, it might be due to the barrel nut catch being worn or the teeth on the barrel nut being broken off. Either part can be easily replaced. Remember to depress the barrel nut catch when tightening the barrel nut to reduce wear on both parts. If the problem persists, an easy cure is to put a rubber or copper gasket between the barrel flange and the barrel nut. Another rare cause of excess headspace is broken trunnion welds. If the welds that hold the trunnion inside the receiver fail, the trunnion will slide forward when firing the gun. Rewelding the trunnion should be done by a qualified gunsmith.
The final cause of failure to fire occurs when the bolt moves forward so slowly that it doesn’t hit the primer hard enough to detonate it. This is actually a type of failure to feed and will be discussed later in the article.
Failure to Eject
Failure to eject is also known as stovepiping. The first possible cause of failure to eject is weak ammo. The heavy bolt and recoil spring of an UZI require a heavier impulse to operate than a typical 9mm pistol. UMC and Remington green box ammo are notoriously weak and can cause failures to eject. If the empty cases are not ejected several feet from the gun, try different ammo.
If ammo isn’t the problem, take a look at the ejector. It should be level, tight and pointing straight forward. It’s riveted to the bottom of the receiver and if it gets loose it won’t firmly strike the back of the fired case as the bolt recoils reward. To tighten a loose ejector, remove the grip frame from the gun, exposing the bottom of the rivet. With the top cover and bolt removed, turn the gun over and rest the head of the rivet on a support,then hammer the bottom of the rivet until the ejector is tight. Once it’s tight, install the bolt without the recoil spring and push the bolt forward and backward by hand. It should pass over the ejector without hitting it. Performing this check with the barrel and stock removed will give you a better view of the ejector clearance.
If ejection problems persist, it’s time to check the extractor, which is the leading cause of failures to eject. The extractor must firmly grip the empty cartridge case as it strikes the ejector in order to generate the energy needed to flip the case out of the gun. Remove and clean the extractor, particularly under the claw, as residue buildup under the extractor claw will prevent it from firmly gripping the case rim. Also, clean the bolt hole that the extractor sits in. A .22 caliber cleaning swap works nicely for this. Residue in the hole will prevent the extractor from flexing properly. Before reassembling, be sure that you have the correct extractor in the gun. 9mm extractors are unmarked while the .45ACP extractors are stamped “45” near the back. They are not interchangeable and it’s best not to mix up semiautomatic and fully automatic extractors as the lower point of the extractor claw is removed on the semiautomatic extractor to facilitate feeding. When everything is clean, reassemble by inserting the extractor through the back of the bolt. Line up the long slot on the back of the ejector with the arrow on the back of the bolt. Reinsert the extractor retaining pin from the left side of the bolt. Using a small screwdriver, try to push the extractor claw sideways. It should require firm pressure but move freely. If there’s no tension on it, the extractor will have to be removed again and bent slightly. If nothing else seems to help,replace the extractor.
Failure to Feed
Failure to feed is the most difficult problem to diagnose because there are many potential causes. A failure to feed occurs when the bolt cannot forcefully strip the round from the magazine and push it into the barrel chamber. The problems fall into three categories: bad recoil spring, excess friction on the bolt, or misalignment of the gun’s components.
A weak recoil spring won’t impart enough energy on the bolt for it to feed a round properly. Recoil springs can get weak with use and it’s good to have a spare on hand; but it’s not a common problem. A more common cause of a spring related failure is aftermarket springs that don’t meet factory specs. Surplus IMI springs are cheap and plentiful so you should replace it at any sign of problems. The entire spring and recoil rod assembly should be replaced as a single piece.
A much more common cause of failure to feed is excess friction on the bolt that can come from several sources. The first thing to check is the gap between the bolt and the top cover. Use a feeler gauge (available at automotive shops) to measure the gap. It should be between .005 inches and .015 inches; preferable about .010 inches. If the gap is too small, the top cover will need to be bent to give more clearance. You don’t need any fancy equipment to bend a top cover; just a little patience and ordinary hand tools. The easiest approach is to flip the top cover upside down and support both ends with blocks of wood. Use a rubber mallet to hammer the middle of the top cover to put a little bow in it. Do it slowly and re-measure the gap frequently. If the gap is tight towards the front or back of the bolt, bend the frontor back of the top cover down. You can get by with a vise and a crescent wrench to bend the ends of the top cover. Be sure the gap between the bolt and top cover does not get excessively wide because it will allow the bolt to slide past the sear without depressing the trigger. That would cause a “runaway” condition and can be extremely dangerous.
If the top cover gap is okay, verify there are no other sources of friction by using the bolt slide test. This test only works on open bolt UZIs. Assemble the unloaded gun without the recoil spring, remove the magazine, put the selector on full auto and hold down the grip safety. While pulling the trigger, tip the gun forward then backward. You should hear the bolt slide freely from the front to the back of the receiver. If it’s binding anywhere you’ll need to find where it’s rubbing and correct the problem. One common cause of binding is trying to use surplus machine gun bolts in a converted semiautomatic UZI that still has a barrel restrictor ring. An IMI machine gun bolt will not have enough clearance and will rub on the top of the restrictor ring. If that’s the problem, the best solution is to have a qualified gunsmith cut off the top of the restrictor ring, leaving just the machined feed ramp.
If friction isn’t an issue, then the problem may be due to misalignment of the gun’s components. First check the magazine. Bent or cracked feed lips will cause misfeeds; so the easiesttest is to try different magazines. The original 25 round IMI magazines are the most reliablefor function tests. Another magazine related problem occurs if it’s held too high in the magazine-well. To test for this you’ll need to repeat the bolt slide test mentioned above, but do it with a magazine body inserted in the gun. You must remove the magazine spring and follower for the test to work. If the bolt rubs on the feed lips during this test, you’ll need to remove the magazine catch and bend it so the magazine is held in a lower position. Check several magazines before bending.
If the magazine alignment looks okay, the other potential alignment problem is much more serious. When the barrel is not properly aligned with the bolt, the round being fed into the chamber will not feed straight in, resulting in a light primer strike or the round jamming between the bolt and barrel. This type of alignment problem is most commonly found on guns built from Group Industries receivers (original Group Industries or some very early Vector guns that were on Group receivers) due to those original Group Industries receivers being somewhat out of spec. Additionally, the heat treating done by both Group Industries and early Vectors warp the receivers and they need to be straightened before assembly, occasionally resulting in misalignment. Straightening a misaligned receiver is not something you should attempt yourself so if everything else checks out on your gun and you’re still experiencing failures to feed, thebest alternative is to contact Vector Arms for their recommendation on factory repairs. Vector will do repair work on any brand of UZI and their customer service is first rate.
The simplicity of the UZI design will allow you to diagnose and correct most problems easily should any arise. With a minimal amount of care, this legendary submachine gun will give you a lifetime of reliable operation.
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|This article first appeared in Small Arms Review V11N4 (January 2008)|
and was posted online on October 12, 2012