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Air Gun Home Forum Index » Rifles » QB78 strip and rebuild Goto page 1, 2, 3  Next    View previous topic :: View next topic  QB78 strip and rebuild   Posted: Thu Sep 22, 2011 1:37 pm Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND I bought another QB78 the other day, a mate wants one for ratting he also wants it fitting with a power adjuster, silencer. Better trigger and a brass breach. So I decided to do two at once as I already have a second hand one in the workshop that requires rebuilding. The last time I did a full QB rebuild on here was four years ago, and since then I have designed a few other custom parts for these cheap and cheerful guns, saying that they are as supplied a piece of junk. But with a bit of work which is mainly stripping the gun down completely, taking off all the sharp edges and polishing the moving parts, a re-crown and a bit of work on the trigger and you have a half way decent gun. So here goes the new QB78 is a SMK XS78 in .177 and the first job is to strip it down. To remove the barrel undo the grub screw in the front of the breach and loosen the barrel band screw, the barrel should now pull out of the breach you may need to clamp the barrel in a vice to remove it, one problem with removing the barrel on a new QB is that you invariably destroy the seals ( Three O rings ), this is because of burr’s on the grub screw hole and the Co2 port. The barrel needed re-crowning and I also wanted to cut a ½” UNF thread on the muzzle to take a standard silencer, before doing this I cleaned out the barrel of the gunge used to protect it from rust, next the loading port was polished and the burr taken off the Co2 port, lastly I did a bit of machining to the loading port to make way for the modified bolt and breach I want to fit. Next the Trigger unit. Al _________________   Posted: Thu Sep 22, 2011 2:07 pm broommaster2000 Moderator Joined: 10 Mar 2007 Posts: 5714 Location: City of Groningen, Groningen, The Netherlands The waterproof bolt is de best thing you've ever come up with in terms of QB78. _________________ BIG GAP   Posted: Thu Sep 22, 2011 7:37 pm AirGunEric Site Admin Joined: 20 Jan 2007 Posts: 6930 Location: "Out There" Geez- with all that "positive" commentary, Al must be a huge glutton for punishment! Why not go with the "Deluxe" model? The ones that have been around North America the last year or so have been infinitely better than the junk here a few years back. _________________ ` I'd say "I care." But I'd be lying. Canadian Airgun Supplier: http://www.scopesandammo.com/storefront   Posted: Fri Sep 23, 2011 3:30 am Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND AirGunEric wrote: Geez- with all that "positive" commentary, Al must be a huge glutton for punishment! Why not go with the "Deluxe" model? The ones that have been around North America the last year or so have been infinitely better than the junk here a few years back. I only want the stock, barrel, valve and trigger and these are the same on both. The rest receiver, bolt, Co2 tube and sights I don't need and these are the extra Deluxe bits you pay for. I cleaned up a Deluxe model for a friend a while back, and apart from the extra bits you get the rest was the same as a standard model rough as a badgers bum. Anyway I thought I'd do a complete strip down and rebuild for a standard QB, and also incorporate the extras I will be putting into these two. I will be handy for anyone new to the QB world of air gunning. I know I go on about them being crap guns which straight out of the box they are, but with out spending anything just a bit of elbow grease and simple tools you can have a very nice shooter very cheaply. I’ve kinder got an affection for them Al _________________   Posted: Fri Sep 23, 2011 7:21 am SMP Silver Status Member Joined: 04 Feb 2011 Posts: 1183 Location: Just south of "Out There"- Land O Lakes Ontario Haha...Ignore the rabble Al and carry on> I for one am looking forward to this story. I agree there is a diamond in the rough under all those scratches and burrs. I just recently stripped and tuned the trigger group on an AR2078. (QB Competition). After two hours of polishing, honing and adjusting I couldn't believe what a gem it was. _________________ Sean TRIGGER   Posted: Fri Sep 23, 2011 12:13 pm Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND Next is the trigger, once I get this done I can fire a few test shots to see how good the barrel is. To remove the trigger unit from the stock turn the safety so that it is pointing down and punch it out from the back, once this is done you can undo the large knob in front of the trigger and remove the unit from the stock, undo the two screws holding the trigger to the valve tube and separate the two. Remove two screws from the cover plate of the trigger and remove it, There is a large spring behind the trigger, undo the screw behind it and remove, this spring can be replaced with a lighter one, this will make the trigger a lot lighter to pull, the other two adjusters are for adjusting the trigger break and travel. Lift the trigger out then release the shear spring and remove the shear. These can now be cleaned and the shear’s polished, you can use a fine stone for this but I use 600 grit emery also don’t overdo it, how well you do this makes all the difference between hitting the target and grazing it. When reinstalling the parts oil the pivots and grease the shears, I use a product called Gleitmo which is a white high pressure paste, but ordinary Molybdenum disulfide will do. You might want to polish the trigger blade while it’s out of the unit. also pack the sides with thin washers to limit the side play. Next the Breach Al Last edited by Alstone on Sat Oct 01, 2011 8:35 am; edited 1 time in total _________________   Posted: Fri Sep 23, 2011 4:02 pm Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND Finalised the design for the new breach, I think it will look pretty smart when its finished. Al _________________   Posted: Sat Sep 24, 2011 3:25 am broommaster2000 Moderator Joined: 10 Mar 2007 Posts: 5714 Location: City of Groningen, Groningen, The Netherlands That'll buff out! _________________ BIG GAP   Posted: Sat Sep 24, 2011 1:12 pm Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND broommaster2000 wrote: That'll buff out! You've got to have a shiny bit. it's something to polish when it's raining. Al _________________ BREACH   Posted: Sat Sep 24, 2011 5:46 pm Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND BREACH The breach and bolt on a QB require very little work apart from cleaning and polishing of the insides. To remove the breach first remove the barrel, then the rear screw of the trigger unit, pull the bolt back and remove the screw underneath the bolt probe, be careful when lifting it off the Co2 tube that you don’t lose the valve to breach seal. The bolt can be removed by inserting an Alan key in the rear of the bolt and unscrewing the grub screw holding bolt handle, be careful not to damage the small O ring on the bolt probe. All the polishing can be done with 400-600 grit emery, if the inside of the tube requires polishing use a wooden dowel with a slot cut in the end, put one end of a strip of emery in the slot and wind it around the dowel and use a drill to spin it. CUSTOM BREACH This is the Custom breach I am fitting instead of the one supplied, not that it is any better apart from it looks nicer, the bolt itself will be customised by fitting a shroud around the probe, stopping rain getting in the pellet loading channel and barrel. If you want to fit a shroud over the loading tray then this how it is done, it keeps the rain from getting into the barrel. TESTING This is the gun assembled for testing to see how well it fires which turned out a surprise, shooting 8.4g AA fields it will shoot 6mm groups at 20m most of the time shooting hole on hole, and 10mm at 30m, this is from a bench rest shooting 500 pellets during the day fps was 738fps average with no flyers, I must admit this the best performance I have seen from a QB, I have yet to fit a power adjuster to it and sort the valve out which should improve things even more. Al Last edited by Alstone on Sat Oct 01, 2011 8:36 am; edited 3 times in total _________________   Posted: Sat Sep 24, 2011 10:04 pm GrizzlyMan Member Joined: 12 Jan 2011 Posts: 80 Least I can say, SUPERB! I just bought two air rifles, one used and another one used at the local Craigslist ads (Crosman RM 377), but cant wait to get my hands on one of these QBs to follow your DIY project. Thanks for sharing high resolution images. _________________ Walther CP 99 compact Walther PPK-S M&P Smith & Wesson Gamo P23 Crosman 357 Umarex EBOS w/ CO2 20ozs mod B1-1 .177 tuned B3-1 .177 B3-1 .22 XS-B12 .22 B2-245 .177 Mendoza RM 377 .177 QB6 .22 tuned QB6 .177 XS-B3-1 .177 XS-B8-1 .177   Posted: Sun Sep 25, 2011 3:50 am Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND GrizzlyMan wrote: Least I can say, SUPERB! I just bought two air rifles, one used and another one used at the local Craigslist ads (Crosman RM 377), but cant wait to get my hands on one of these QBs to follow your DIY project. Thanks for sharing high resolution images. You won't regret it, well worth the effort Al _________________   Posted: Sun Sep 25, 2011 7:10 am SMP Silver Status Member Joined: 04 Feb 2011 Posts: 1183 Location: Just south of "Out There"- Land O Lakes Ontario Can anyone else see the problem with Al's new bolt in the first picture of the bolt and breach laying side by side _________________ Sean   Posted: Sun Sep 25, 2011 7:38 am Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND SMP wrote: Can anyone else see the problem with Al's new bolt in the first picture of the bolt and breach laying side by side ? Al _________________   Posted: Sun Sep 25, 2011 8:01 am SMP Silver Status Member Joined: 04 Feb 2011 Posts: 1183 Location: Just south of "Out There"- Land O Lakes Ontario The cocking flats are facing up. Does that mean your an upside down cocker _________________ Sean QB78 strip and rebuild     Air Gun Home Forum Index » Rifles You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum All times are GMT - 5 Hours   Page 1 of 3   Goto page 1, 2, 3  Next All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First  Select a forum Main Forums----------------AirGunHome Q&AGeneral Air Gun Questions and TopicsPicture GalleryTarget Shooting: Casual, Fun and CompetitionHunting, Pest Control, Varminting People/Events/Airgun Issue Discussion----------------Introduce YourselfThe BS TopicClubs/Events/Regional/Political Airgun Issues Maintenance, Modification and Reviews----------------RiflesPistolsAntique, Collector and Novelty AirgunsBB GunsPellets/AmmoOpticsAccessoriesAirgun Smithing Buy, Sell or Trade Forums----------------For SaleWant to Buy   Note: If you are seeing "Please enter your username and password to log in." 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