The QB78 CO2 Pellet Rifle - Airrifle.co.za ¤ Passionate About Air Rifles
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1. Squeezing the Trigger causes the Sear to fall allowing the Hammer to move forward rapidly under pressure of the Hammer Spring The Hammer impacts the Valve Stem and is then arrested by a stop spacer and the back of the Valve Seat The Valve Stem continues forward opening the Valve Seat and transfer port to an inrush of CO gas The Valve Stem continues its forward travel driving the Piercing Pin forward and compressing the Valve Spring The pellet is launched by the released gas and starts its journey spinning down the Barrel The Piercing Pin is driven into the welded seal of the rearward facing CO cartridge piercing it if it is still sealed Note that the foreward facing CO cartridge is pierced during loading by a separate piercing pin in the tube cap A FEW MILLISECONDS AFTER FIRING sl _ es O Wesce et The compressed Valve Spring eventually extracts the Piercing Piece from the CO cartridge and presses it back against the Valve Stem which is forced back against the Valve Seat This stops the flow of gas just as the pellet is about to exit the Barrel and the starting conditions are reestablished About CO Your QB78 rifle uses two common 12 gram Powerlet CO cartridges This is sufficient energy for about 60 full power shots 1f used within a temperature range of about 60 to 80 F The Powerlet wraps 31 5 grams of deep drawn steel around 12 grams of liquid and gaseous carbon dioxide CO2 lockin2. AO This is a second focusing adjustment allowing the scope to be used at close distance 10 yards or less The first focusing adjustment is for the eyepiece and it compensates for your eye Your QB78 has receiver grooves that will accept standard 11 mm airgun or airgun rimfire rings Note that these are different from Weaver mount rings For best results use the lowest saddle height rings possible This keeps the scope axis as close to the bore axis as possible 1 Prepare the rings for application If they contain recoil stop pins remove them as the QB78 has no mating stop pin holes Remove the caps from the ring bases 2 Mount the bases to the receiver Only hand tighten the clamp screws you need the bases to slide freely at this point 3 Fit the scope into the bases Slide one of the bases until the spacing is right about the scope s central turret Add the ring caps but only hand tighten their screws Hold the rifle in firing posture Slide the scope back and forth until you achieve a position that lets you see through the optic with the least tunnel vision Lock the base screws at this location Twist the scope body to align the graticule vertical line up and down Then tighten the cap screws If necessary use a 2 Phillips screwdriver to remove the two screws securing the rear iron sight Save these pieces for future use Install scope accessories such as filters
3. 17 5 sight radius Barrel 21 4 inch 543 mm target grade steel Energy Source two 12 gram CO Powerlet cartridges Stored Energy typically sufficient for 50 60 full power shots Length Overall 40 inch 1015 mm Length of Pull 14 in 355 mm Weight 5 75 lb 2 6 kg Powerlet is a registered trademark of the Crosman Corporation Setup Before using your new rifle inspect it carefully to assure that all parts and accessories are present and that no shipping damage has occurred Retain the shipping container and packing in the event that subsequent service 1s required Be certain the rifle is unloaded before doing anything else Check to see that the bore is unobstructed Be certain the gas tube cap can be turned by hand Verify the bolt trigger and safety functions Operation Installing CO Cartridges 3 Open the Bolt as illustrated above Opening the bolt leaves the loading chamber open to inspection More importantly retracting the bolt prevents dangerous accidental piercing of the rearward facing CO cartridge 1 Verify that the Gas Tube Cap can be 4 Unscrew the Gas Tube Cap from the Gas loosened by hand as shown above Never Tube and set it aside Slide two 12 gram use a tool to rotate this cap A tight cap CO2 cartridges into the Gas Tube back to indicates dangerously high gas pressure back as shown above Note for shorter remains within the Gas Tube shooting sessions load an empty cartridge as the rearward
4. The QB78 CO Pellet Rifle ew _ J A U ser S M an ual Text photos and illustrations by George Fox Lang An introduction to using the classic QB78 pellet rifle one of the nicest and most popular CO rifles ever produced The QB78 is a svelte sculpture in steel and hardwood sold at a bargain price It provides low priced entry to the world of precision airguns and unending opportunities for the adventurous experimenter George Fox Lang 2006 All Rights Reserved Distributed exclusively by Neither this manual nor any of its content may be Flying Dragon Air Rifles reproduced or copied for any commercial purpose without the written consent of the author About the QB78 The QB78 is a modern classic manufactured by the Shanghai Air Gun factory and sold worldwide under the ndustry brand It is a compact and handsome CO powered rifle made of blued steel and hardwood It is amanly weapon with nothing toy like or plastic about it The QB78 exhibits power and accuracy matching its good looks It was patterned after the no longer manufactured Crosman 160 and 167 airguns SPECIFICATIONS Type single shot bolt action Caliber 177 4 5 mm or 22 5 5 mm Muzzle Velocity 600 FPS 177 or 420 FPS 22 typical within 60 to 80 F Accuracy 0 5 inch center to center at 10 yards typical Trigger Single stage adjustable for tension over travel sear engagement Sights open iron sights rear adjustable for elevation
5. cap mounting screws provided with your scope rings Only hold the short side of your Allen wrench when tightening scope screws Theory of Operation The following figures are not scale drawings of the QB78 parts they are schematic diagrams intended to explain how the rifle functions Some artistic liberties have been taken for clarity of explanation ARRANGEMENT OF PARTS a The Breech Tube 1 contains the Bolt 2 and is attached to the Barrel 3 by a setscrew and O rings It sits atop the Gas Tube 4 to which it is screwed An O ring seals a gas transfer path between the Valve Body 8 contained in the Gas Tube and the firing chamber sealed by an O ring on the Bolt The Gas Tube 4 holds two CO cartridges 5 back to back The reward facing cartridge is in front of the Piercing Pin 6 the Valve Stem 7 and the Valve Seat 8 A Valve Spring 9 surrounds the Piercing Pin and reacts against it and a fixed spacer The rear of the Gas Tube houses the Hammer 10 and Cocking Piece 11 These parts are surrounded by the Hammer Spring 12 which reacts against both of them Note that pins are fitted to the Hammer and Cocking Piece These pins connect these parts mechanically with the Bolt through facing slots in the Breech Tube and the Gas Tube The spring supported Sear 13 protrudes into the Gas Tube from the Trigger Casing Assembly screw mounted to the bottom of the Gas Tube The sear is a cam like device that can hold the Hamm
6. er in a rearward position until the Trigger causes it to fall away As shown above the rifle has been fired and the bolt remains closed on an empty chamber Both the Hammer Spring and the Valve Spring are in their relaxed but preloaded conditions CO gas fills the front portion of the Gas Tube but is blocked from further infiltration by the Valve Stem pressed firmly against Valve Seat by the Valve Spring The Hammer rests upon the Valve Stem in this equilibrium OPENING THE BOLT Raising its handle and pulling the Bolt 2 to the rear moves the Hammer rearward through action of the Hammer Pin The modest compressive preload of the Hammer Spring is retained against the bolt through the Cocking Piece Pin With the Bolt open a pellet can be placed in the mouth of the firing chamber CLOSING THE BOLT a a Pushing the Bolt forward and lowering its handle cocks the weapon and locks the pellet in the firing chamber ahead of the gas transfer port The pellet 1s forced into the Barrel s twisted grooves and the O ring on the Bolt seals the chamber behind it As the Bolt moves forward the Hammer and Cocking Piece follow it Forward motion of the Hammer is arrested by the Sear which stops the Hammer about 7 16 before it can contact the Valve Stem The Cocking Piece moves forward about an inch compressing the Hammer Spring The rifle is now ready to fire FIRING THE RIFLE C M wa gt E e ooo o a a i ia
7. facing first installed cartridge This will give approximately 30 full power shots 2 Apply the Safety by swinging it to the rear as shown above 5 Screw the Gas Tube Cap back on fully this will pierce the forward facing CO cylinder When the cap has seated fully hand tight back it off a quarter turn This will allow the CO to flood the Gas Tube Do not forget to back off or the forward facing cartridge will remain sealed by the Gas Tube Cap 6 Check that the chamber is clear Operation Shooting Basic operation of the rifle is very simple To fire a pellet 1 Lift the Bolt Handle and pull it fully to the rear to open the breech 7 Close the Bolt cocking the rifle 2 Insert a pellet of the proper caliber into the open breech Make certain the pellet enters nose first with the fan tail skirt to the rear as shown 8 Release the Safety by rotating forward and out of the trigger guard 3 Push the Bolt Handle fully forward and rotate it down This seats the pellet into the rifling and seals the breech The weapon is ready to fire 4 Aim at your target place your trigger finger within the Trigger Guard and squeeze the Trigger gently 9 Point the rifle in a safe direction and pull the trigger A mild report pop verifies the weapon is now charged with CO and is ready for shooting Trigger Adjustments The QB78 trigger features three adjustments A Tension
8. g it in a hermetically sealed vault with a minimum burst pressure of 7000 pounds per square inch psi pressure The bottle is smooth and seamless providing a precisely controlled 14 cc volume sealed by a pierceable steel plug welded to the bottle s neck SECTIONED VIEW OF A POWERLET The Powerlet contains a considerable amount of energy over 280 ft lb or 380 Joule This is approximately equivalent to two high velocity 22 long rifle shells or one 38 Special P cartridge To place this in another perspective the contained energy is sufficient to light a 100 Watt bulb for nearly four seconds Any one of these equivalents is clearly capable of injuring you the CO cartridge must be treated with care and respect When used near room temperature it 1s capable of delivering most of this stored energy as useful muzzle energy Fifty slow fired shots of 600 foot per second fps velocity with a 7 1 grain pellet 5 7 ft lb muzzle energy is a reasonable expectation If the firing pace is slow and deliberate these shots will exhibit remarkably consistent velocity owing to the built in pressure regulation provided by thermodynamic interplay between the liquid and gas phases of CO Powerlet is a registered trademark of Crosman Corporation 10 100 90 80 70 60 50 40 Percent Mass 30 20 10 0 0 20 40 60 80 100 120 140 160 Temperature F The critical temperature of CO is 87 8 F a
9. hanism provided by CO Consider what happens when a mass of CO is sealed in a fixed volume container If the mass to volume charge density is equal to the 0 468 g cc critical density the pressure within the container will exactly equal the vapor pressure for any temperature below the 87 8 F critical temperature If a larger or smaller mass of CO is present the pressure versus temperature line will depart from the saturation line at a temperature below 87 8 F as shown below CO Remaining 6000 5000 4000 3000 Pressure psig 2000 1000 Temperature F This figure presents the pressure within a Powerlet as a function of temperature with from 1 to 12 grams of CO remaining in the bottle Note the blue segment partially common to all of these traces this is the saturation line A CO charge of 6 55 grams remaining in the 14 cc cartridge volume 0 468 g cc will exhibit a pressure versus temperature curve that follows the saturation line all the way to 87 8 F all other charges depart from the blue line at a ower temperature The point of departure from the blue segment is termed the transition point defining a transition temperature and a transition pressure Above the transition temperature the CO behaves as a gas with pressure rising with increasing temperature When the Powerlet is essentially full the slope above the transition point is very steep and pressure rises rapidly w
10. ith temperature to potentially dangerous levels 11 When the cartridge is nearly depleted the transition point marks the end of useful life This is the point at which all of the liquid CO has been consumed Re plotting this data with a different format makes the natural regulation process more evident The following plot presents a family of pressure versus mass lines each for a different ambient temperature Note the broad constant pressure horizontal segment in each line below the dotted 87 8 F curve 1500 1400 1300 1200 1100 Pressure psig _ NOAA OaonN wo OO ooooo OO CO oO ey fe O OOOO OOT 100 10 11 12 Coz Remaining in 12 gram Powerlet g CO regulation is summarized below Mark the ambient temperature on the horizontal scale and read the corresponding pressure and mass limits directly above it For example on a 70 F day a regulated pressure of 840 psig will be provided as long as the Powerlet holds at least 2 8 grams but not more than 10 6 grams of CO Hence the first few shots will be hot until you use 1 4 grams from a new Powerlet You will run out of liquid when 2 8 grams of gas remain in the cartridge 13 12 11 10 9 8 i 6 5 4 3 2 1 0 40 45 50 55 60 65 70 75 80 85 90 Temperature F gon Air Rifles Specializing in OB S series COQ rifles tested for reliability adju
11. nd this temperature is of particular importance to air gunners As shown in the graph above below this temperature both gas and liquid CO coexist in the Powerlet Above this temperature only gas can be present The cartridge exhibits a natural pressure regulating mechanism but only at temperatures lower than 87 8 F At low temperature the bulk of the entrained CO is in liquid state As the ambient temperature rises heat enters the cartridge and some of the liquid boils to gas the percentage of gas in the mixture increases as does the pressure Below 87 8 F the boiling stops when the pressure reaches the vapor pressure determined by the ambient temperature as long as some liquid remains Above this critical temperature all the CO boils to gas When a shot is made some CO gas exits the cartridge rapidly and the ratio of gas to liquid 1s instantaneously reduced The loss of gas reduces the pressure within the cartridge causing some of the liquid to boil or vaporize to fill the void This vaporization extracts heat from the mixture cooling it The mixture continues to boil liquid to gas increasing the pressure while drawing heat from the ambient temperature surroundings Eventually the mixture warms back to the ambient temperature and the boiling stops when the pressure reaches the vapor pressure Hence the next shot will be made from exactly the same pressure source This is the natural pressure regulation mec
12. or trigger force factory set to about 4 Ibs turn screw counter clockwise to reduce Setting tension below 2 Ibs may result in accidental discharge if the rifle is dropped B Over travel or backlash factory set to about 0 25 turn screw clockwise to reduce Turning screw too far clockwise will prevent the rifle from firing C Sear Engagement or pull length factory set at about 0 125 turn screw clockwise to reduce Reduced sear engagement may result in accidental discharge if the rifle 1s dropped To Make Trigger Adjustments Unload the rifle before making adjustments 1 Place the Safety lever in the SAFE position and push it out of the Trigger Casing from left to right Use the eraser end of a wooden pencil as the dismounting tool 2 oS Unscrew the Locating Screw Nut and remove the action from the stock Use a 2 Phillips head screwdriver to remove the two Casing Plate Screws Lift off the Casing Plate to expose the trigger mechanism Use a 2 mm flat jeweler s screwdriver to adjust the Sear Engagement and Overtravel screws Use a 3 16 flat screwdriver to adjust the Tension screw Reassemble the rifle by following these instructions in reverse sequence Mounting a Scope One of the most popular options for any airgun is a telescopic sight The QB78 is an accurate rifle and it fully deserves a good quality optical sight If possible choose a scope with an Adjustable Objective
13. sted for accuracy polished for smoothness and tuned for ar ee 57 iy 5 maxirnum performance in 3 Ey ea J e Pep a j www ai gunartisans com flyingdragon ARZOTEA ARZOTSA
14. sun shades and lens caps If desired use a 7 8 flat bladed screwdriver to remove the front sight Zero the scope to the rifle by firing from a steady rest Start at a close distance and work out Optical Adjustments 1 Physically position the scope fore and aft from your eye When properly positioned the scope will present a full field of view free of tunnel vision Your eye 1s now within the eye relief of the scope Note when fitting a short or mini length scope such as the Leapers 6x32 Bugbuster illustrated you may have to compromise this position to leave the breech clear of the scope s front bell 2 Focus the eyepiece or ocular adjustment to provide a crisply defined graticule Viewing an uncluttered target such as a light colored painted wall makes this adjustment simplest 3 Set up a target at the desired shooting distance Focus the front bell or side wheel parallax adjustment to provide a clear image of the target When both the graticule and the target are in sharp focus the two images are in the same plane within the scope This allows your eye position to move without affecting the point of aim 4 Adjust the windage and elevation of the scope to force the point of impact to converge with the point of aim Do this as an iterative process starting at close range and incrementally moving back to your desired target range Use care not to over torque the small base and
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