The following is a joint work in progress between K2 and myself. I hope it helps.
This is an attempt to help get more Uzi F/A 22 conversion kits running. The sequence of adjustments is important. About 70% of the guns can benefit from tuning. Think finesse as opposed to brute force when tuning! Any operation that uses live ammo shall only be performed without a barrel in the gun.
Step 1: 22 conversion bolt - Verify that the steel sear surface is not loose in the bolt. Repair as necessary. Examine the sear surface of the bolt for a raised burr on the bottom surface. Remove the burr if it is present. Examine the 22 extractor. It should be tight on the firing pin/breach face insert. This may be tightened by removing the extractor and gently tapping (with a small hammer) the legs of the extractor together. This can be done several times before the extractor cracks & fails. Before reinstalling the extractor break all the edges that project ahead of the bolt face. Be careful around the hook of the extractor. The edges just need to be broken enough so the so they are not sharp.
Step 2: Bolt friction in the receiver. - Remove the 9mm barrel, bolt, and recoil spring. Drop the 22 bolt into the receiver w/o the top cover or recoil spring. With the fire select on F/A, pull and hold the trigger with one hand while cycling the bolt with the other hand. There should be no binding felt at all while moving the bolt. Remedy any binding or interference. Frequently the muzzle end of the ejection port cut on the receiver hangs on the bolt. Do not file or grind your receiver. Carefully bending of the receiver to the desired shape should be performed.
Step 3: Top Cover – Top cover/bolt fit is important in a 22 conversion kit. A sloppy top cover can keep the extractor from working correctly. Adjust the top cover for a minimum bolt/top cover clearance. Do not test this with ammo or a magazine in the gun! Verify that there is no binding by installing the 22 bolt & top cover without the recoil spring. Set the fire select to F/A and pull the trigger. Tip the muzzle down and up. The bolt must slide freely all the way forward and back w/o binding.
Step4: Extractor Height – Apply layout dye to the extractor grooves in the 22 barrel. Install the 22 barrel, 22 bolt, recoil spring, and top cover. Cycle the bolt and read the wear marks in the extractor groove on the barrel. Shim the firing pin/bolt face insert (if required) to center the extractor in the barrel extractor groove. The shim pack (if required) is normally between .005” and .012”.
Step 5: Feed Ramp - If after adjusting your extractor height the bolt hits the surface between the feed ramp and the chamber you will need to have this area clearanced just enough so the bolt clears. The top and bottom edges of the feed ramp should be radiused and the sharp edge of the chamber should be slightly chamfered and polished so it doesn't shave the bullet as it is feeding into the chamber.
Step 6: 9mm Ejector – With the bolt, barrel and top cover removed, insert a 22 magazine with several rounds in it. Verify that the 9mm ejector doesn't strike the rim of the 22 cartridge in the magazine. If it does, trim the nose of the 9mm ejector back until the rim just clears. Keep the 9mm ejector face perpendicular to the bore axis.
Step 7: Recoil Spring – A dedicated 22 recoil spring is often necessary. Verify that the guide rod in the spring is straight. This can be done in a lathe or remove the rod from the recoil assembly and roll it on a flat surface. Most kits will benefit from a reduced spring coil count also. Coil count is not a really good way to measure spring force but it is a start. 100 active coils is a good starting point. For BWE Slow-fire kits, it is easy to verify the spring force. Set the spring “buffer” on a table with the spring vertical and set the bolt in place on the spring. The end of the guide rod should be even with the front of the bolt. If it sticks out, you may have cut too many coils from the spring. If it doesn't come flush, carefully cut coils until the guide rod is flush with the end of the BWE Slow-fire bolt. This is only a guide. Some guns need more or less spring to run. (Hot ammo, M-22, Dynapoint & CCI etc., are easy to get running. Federal bulk can take some careful tuning.)
Step 8: Magazine Height – Install the 22 bolt w/o recoil spring. Remove the spring and follower from your 22 magazine. Insert the magazine into the gun. With the magazine pulled down onto the mag catch, verify that the 22 extractor and “stripper” (the portion of the bolt that strips the round from the magazine) clears the feed lips on the magazine. This distance is normally set to 0.020”. To adjust the magazine height, bend the tab on the mag catch that engages the magazine slightly upward or downward. (The magazine release on the Uzi is regenerative. In other words the magazine must move upward before it can move downward. This will limit how much you can raise the magazine by bending the tab that engages the magazine. You know when you have gone to far when you can not remove the magazine as the stops on the magazine hit the bottom of the grip assembly before you get the mag released!) 9X19 is normally not effected by slight changes in magazine height. 22RF is not as tolerant.
Step 9: Lubricants, The Gun – I have had the best luck with Teflon based lubricants. Apply sparingly on clean surfaces. If a dry towel wipe is used to clean out the powder residue in the gun, re-lube is not necessary each cleaning.
Step 10: Lubricants, The Magazine –Clean & dry the inside of the magazine by pushing patches of paper towel or your favorite cleaning patch. Spray a little Teflon lube on a patch and run it threw the magazine. You want a very thin film of lube on the inside of the magazine. If subsequent cleanings are done with a dry patch to get powder and lead shavings from the magazine, re-lube is not required unless sticking occurs.
