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Note: Xinhua airguns were made by a Factory 972 (AKA Xinhua Machinery Factory) - a light weapon factory in China

Improving Accuracy in B2 Air Rlfles

Gary Finch
September, 1999

        At this time, one of the most popular inexpensive Chinese air rifles is the B2-1, which is a breakbanel design that is very similar to the older RWS-Diana air rifles. There are several Chinese-made variations of this design; in my opinion one of the best is the Xinhua Factory Model B2, which is a breakbarrel .177 cal. design nominally rated at 700 fps.

The Xinhua made B2-1 is currently selling for $25~28 in this area, while the Industry Brand B2-1 goes for$20 - $25.

        This is dirt cheap for any type of decent air rifle, but of course you have to forego the niceties of an attractive, wellfinished stock, and well polished and evenly blued metal work. Still, these guns have basically sound actions and barrels, so they have the potential of good accuracy and power. What they lack is any type of quality control or final inspection, because they frequently have serious (but easy remedied) manufacturing defects.

        To intelligently begin this discussion, we must first ask, what constitutes good power and accuracy in a sprin~piston air rifle? I'm not speaking here of 10 meter Match quality rifles, wNtch often cost over $1,000, but ot sporting-type air rifles like the RWS Model 36 or Beeman S-1. Studying the offerings of the major European manufacturers, we find that the better rifles have a muzzle velocity of 700-1,000 fps, with a consistent accuracy capability of 1. groups at 25 yards and 2" groups at 50 yards, so these should be our standards in any sprin~piston air rifle.

Inspecting The Gun

        First check the airgun for any broken or malfunctioning parts: does the action and barrel appear straight and tight? Does the cocking mechanism and trigger function properly? Is there any residue of preservatives (heavy oil or grease, Cosmoline, etc.) still within the action or barrel that must be removed before shooting? If so, remove it with soft rags and a gentle degreaser. This is a common problem with these guns, whkh are often heavily coated with preservatn/es before shipping by boat from China. Inspect the external metal finish; if it has a coat ot surface rust, remove it with WD40 and paper towels. Paper towels are mildly abrasive and will remove a without scratching the blueing. Inspect the barrel for metal chips or excess oil; clean if necessary. After cleaning off the surface rust be sure to apply a good coat of rust-preventative gun oil. Now that the gun is clean, check the action screws (screws that secure the action to the stock) for tightness, and tighten if necessary. (There are typically 2 screws securing the forend to the breech and 1 screw through the trigger guard to secure the recoil lug of the action to the stock.) While tightening the recoil lug screw, check to be sure that no part of the stock is in contact with either side of the tr gger. These guns are crudely inletted, and it's common to have to remove a lime wood trom one side or the other to allow free movement of the trigger. After completing the above items, you are ready to fire the gun. First try a close range shot of 5~10 yards at a large target to determine where the sights are set. Most B2 s will usually shoot high out of the box. The B2 has only an elevation adjustment, but if the windage (lelt to right) is off you can bend the front sight post slightly left or right to change it. On the ones I've seen, if you set the elevation adjustment to the 10 meter position, the gun actually will zero in at about 25 yards. In some extreme cases it is even necessary to file the rear sight notch deeper to get a proper zero, but remember this will also depend on the weight of pellet you are using, so possibly using a heavier pellet will correct this problem. Once the sights are properly adjusted, shoot a few 5-shot groups at 10 and 25 yards to assess the bas~ accuracy of the gun. Some guns will shoot good groups right out of the box, while others may shoot very poor groups at 10 yards. If the gun simply will not group well, try a different brand and/or weight of pellet. I've found these .177 caliber guns will generally shoot best with pellets in the 7.5~8.5 grain weight range, but each gun is different, so it pays to try different brands. Generally, Gamo and Daisy pellets, which are made in Spain, shoot well in the B2. The Gamo Hunter domes, which weigh 8.4 grains, have always shot quite well for me, as have the pointed Magnums.
 

It's the Little Things That Countl

        Start with the simple things: are the sights still set correctly? Are you holding the gun correctly when you shoot it? Are you holding your sight picture long enough for the pellet to exit the banel? Springpiston airguns don't shoot well when gripped too tightly, its best to hold them only tight enough to keep the sights on target, since the mainspring recoil produces a double recoil effect. This invariably causes muzzle "flip" when the gun is tired, which throws the gun off target before the pellet can exit the bore. (This is a characteristic of all spring-piston type airguns). They also do not shoot well when tightly held in a nfle rest, typically shooting high and often printing groups with two different points of impact on the target. The best way to shoot accurate~ with them at longer ranges is to rest your body against a solid object tor steadiness, but allowing the gun to only contact your hands and body, not another solid object.

        Now, let's suppose that up to this point you are doing everything right, and still can't get the gun to shoot good groups. If this is the case, we must assume that something is mechanically wrong with the nfle which is causing some shots to go astray. Starting with the most likely problem, is the gun correctly lubncated? Spring-piston airguns must compress the same volume and pressure of air behind the pellet every time to shoot accurately and consistently. In the B2-1 the only seals are the flat steel faces of the barrel and the the breech face. Shoot the gun while holding your hand over the joint of the barrel and breech. If you feel air blowing out during firing, the faces of the breech and barrel are not fming tightly enough to seal completely. First try tightening the barrel pivot bolt to correct this. Loosen the
 the smaller lockdown screw, then tighten the larger barrel pivot bolt to to make the breech to barrel a snug fit.

        Temperatures may exceed 1,000 degrees F. in the air chamber during firing, and the air cylinder seal needs a lubricant with light viscos ty and high flash point to withstand these conditions. Chamber oil also preserves the seals and lubricates the chamber walls to allow maximum air piston speed during firing. The piston seal of most BZs is a compressed leather seal, the same type as was used in older model Diana air rifles. This seal does an excellent job as long as a is properly lubricated, but if a dries out too much it may allow air to blow by the piston, whkh results in inconsistent velocity, and may cause inaccuracy. This leather seal see ns to be something of a standard on the inexpensive Chinese airguns, since it's also used on the B3 1's, etc. (see assembly drawing on last page). Another important point of lubrication is the mainspring and guides; poor lubrication here leads to an inconsistent piston stroke, again causing inaccuracy. This is easily done without disassembling the action. This is done by removing the action from the stock and then applying oil through the long mainsprir~ slot in the bottom of the action. A heavier oil is needed to lubricate the mainspring, since there is no temperature problem here, and we want the oil to stick to the mainsprir~ and spring cylinder walls. Both Beeman and RWS make a fine line of airgun lubrication products, but many industrial lubricants are also well suited for airguns. For example, I've used Mobil DTE Lite hydraulic oil as a chamber oil, and Mobil DTE 26 as a mainspring oil with excellent results, and they are readily available in most tactorys. Various Moly (molyWenum disulphide) compounds are also excellent for lubrkating mainsprings, barrel pivot points, etc. One that I particularly like is Hytemp by Asinco; this is an industrial moly lube and ant-seize lubricant compound that comes in an aerosol spray can, making it easy to apply a in tight spaces. This moly spray has the advantage of spraying on wet, then drying to a hard moly coat that resists wear while still providing good metal-to-melal lubrication. MsMoly, whkh is used by firearm shootets to lube bullets, is a similar compound, and also works well.

If at this point the gun still refuses to shoot accurately, the last place we should check is the barrel crown.

        For an airgun to shoot accurately, each pellet must exit the barrel the same way every time, ideally leaving contact with the rifling at the same moment on all sides. This is the purpose of barrel crowning, which is grinding or lapping a small ball-shaped relief a few thousandth's of an inch larger than the bore into the end of the barrel. There's no big mystery about crowning a barrel; a just requires careful attention to precision. It can be done quite quickly and easily with a Dremel tool and a small tapered stone with an end smaller than the rifle bore. I prefer the small rechargeable Dremel tool for this, since It turns at much slower RPM than the 120 V. AC tool, as our aim is to remove only a small amount of steel in the very end ot the bore. Just be sure the stone Is square to the bore and you grind it evenly on all sides. It's also a good idea to finish up by polishing the crown with a little piece of Scotchbrite or crocus cloth. Just wrap it around the small tapered stone and use the Dremel tool to polish with. This  will often produce an immediate and dramatic accuracy improvement. By the way, this  also goes for the breech chamber in all break-barrel airguns!

        This is the point where you insert the pellet into the barrel. If this is not cut deep enough, a little of  the
pellet base may protrude. and be smashed or cut off when the the breech is closed, again causing inaccuracy. Olten
just a little polishing here with the Dremel tool and Scotchbrite will improve the pellet fn in the breech chamber
considerably.
 

B2-1 Tune-up List

        In order to make it easier to keep track ot all these items. I've listed them in order below.
(Note: Be sure the gun is not cocked. and refer to the assembly drawing on the last page for these items!)

(1 )    Remove the action from the stock, then remove the lockdown screw and barrel pivot bolt to separate the barrel from the action. This will then allow you to remove the cocking lever linkage, which fits in a slot on the bottom of the air piston.

(2)     Using a spring compressor, compress the mainspring and remove the mainspring retainer pin. Then remove the trigger, trigger sear, and trigger return spring while the spring is still compressed.

(3)     Ease off the spring compressor until the mainspring, rear gu..de, and spring follower can be removed from the spring cylinder. Note the skit in the bonOrn of the spring fdlower for the trigger sear; if it has any rough edges, remove these with a needle file or Dremel tooll

(4)     Now remove the air piston from the spring cylinder by grasping the front guide, which is  part of the air pston. This may be a tight m; if so, you may need to use a turning motion while pulling. Be careful not to damage the sides of the leather seal on the cocking linkage cutout in the spring cylinder! If it has rough edges, deburr them as descibed above.

(5)     With the air piston assembly removed, check for proper lubrication and gen0al condition of the seal. If the seal is dry, soak overnight in a good hydraulic oil as described earlier in text.

(6)    Inspect the mainspring and guides for damage or wear. If they are okay, lube mainspring and guides with either spring cylinder oil, or a good quality light grease. (See text below for recommendations).

(7)     Modify the trigger sear as shown in the assembly drawing; do not remove any metal from the ~ont face of the sear. Grinding this down may cause too little sear contact, making the gun unsafel Lube the top of the sear, and the spring retainer pin hdes in the trigger and sear (see further text)

(8)     Before reassembly, lube the inside of the spring cylinder, checking to be sure the transfer port (the hole in the front of the air chamber) is clear. Also check the breechbarrel faces, clean if necessary!

(9)     Reassemble the action, taking care that the leather seal ~s not damaged by the edges of the cocking lever slot. When reinstalling the mainspring retainer pin, remember that the trigger and sear pivot on  it, and must be installed with the spring compressed! Alter the trigger, aear, and retaining pin are installed, use needlenosed piers to reinstall the triggger retum spring. Aftter the action is completely reassembled, reinstall the cocking lever linkage, then reassemble the barrel to the breech.
        (Note: Don't forget to lube the barrel pivot bolt; moly grease is good here!)

        Before reassembling the action in the stock, cock the gun, insert a pellet, and then fire to verify proper operation If everything is okay, reassemble the action in the stock. (Note: poor stock-to- action fit can cause inaccuracy that no tuneup can improvel If the action does not sit solidly in the stock before installing the action screws, remove wood from the inside of the stock at the points which prevent solid contact. This is especialb, important in the recoil lug area (rear stock screw)'

        If you have faithfully followed all the above steps, your B2-1 will now be much more accurate, and have a much lighter and smoother trigger pull. Remember that accuracy is also a function of the quality of your pellets, and price is not always a good indicator of quality! I've found that good quality domed and pointed pellets seem to shoot well in these guns, and pellets in the 7.~8.5 grain weight range seem to do best. RWS Superdomes, Gamo Hunter domes and Magnum pointed, and Beeman Silver Stir~ pointeds all have shot well for me. What kind of accuracy can you expect after luning up your B2-1 ? Well, I currently have two on hand; one consistently shoots 1.5" groups at 30 yards, the other 1 .25" groups at the same distance. Both will shoot 0.5" groups at 10 yards, and I think this is very satisfactory performance for airguns that cost less than $30. Muzzle velocity was also greatly improved by this tuneup procedure; both guns averaged 650~670 FPS with 8 grain pellets before tuneup, and this increased to 740~760 FPS afterward. It doesn't cost much to improve these guns, just a little time and effort, and in the process you'll leam a lot about break-barrel air rifles. Remember that the leather piston seal needs lubrication; a couple drops of chamber oil applied directly into the transfer port every 20~300 shots is sufficient. After oiling the seal, it usually takes 20~30 shots for the gun to settle down and start shooting consistently again. Cleaning the barrel every 400~500 shots is also recommended for best accuracy. By the way, don't forget that this tuneup procedure does not apply only to Chinese airguns; it is just as effective on any break-barrel cocking airgun, regardless of the manufacturer. Good luck, and good shooting!
 
 

Test Shots of Tuned XinHua B2 Airgun

Distance: 30 yds., Scope:  BSA 3-7x20 mm,   Date: 9-9-1999

TF Match Heavy Wadcutters  (see note)
5 shots,  Group 7/8"  ,  G.F.

Daisy MaxSpeed Wadcutter 
5 shots ,  Group 1 5/8",  G.F.

Gamo Match Wadcutter, 
5 shots,  Group 1 3/4" ,  G.F.

Further Notes on Lubrication

The mainspring and piston can also be lubed with either moly grease, or a dry moly spray if desired.  My own personal preferred method is as follows:

(1) Thoroughly clean both the spring and piston with a good degreaser.
(2) give both the mainspring and piston a good coat of moly spray, such as MsMoly or Hytemp. Don't
try to spray it all on at once, give it two light coats for good coverage, letting dry completely between coats. Give the
bearing surface (sides) of the seal one light coat. Let the moly cure for at least an hour or two to make sure its
completely dry.
(3) Now give the mainspring, guides, piston body, and sides of the seal a light coat of a good clear teflon grease,
such as Selig Chemicals "CIear Lube", or Asinco's "SPX-50". (Note: these are industrial products, but most auto parts stores sell similar products. Just look for a light bodied seflon spray grease with a maximum working
temperature of 500 degrees F., because some of the grease will eventually work .its way into the air chamber through
piston action.

        One big advantage of this method is that it is long term lubrication, often lasting tor years. Alternatively, one can simply lube themainspring, guides, and piston body with spring cylinder oil or moly gtease. If you use moly grease, a little goes a long way!  Don't overdo it, or most of it will wind up on the inside of the stock, staining everything in side!
 

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