Hercules/Cummins B-3 Rifle
By: R. Sauer & V. Palitang
to the B-3 rifle
Identifying the B-3 features
Basic Lube Tune
and piston weighting
seal expansion washer improvement
a muzzle brake for the B3
Introduction to the B-3 rifle
The B-3 is manufactured by Industry Brand of China and
can often be found under the name of Cummins and Hercules or simply
called the B-3. It is an underlever rifle that is available in both
.177 and .22 caliber. Typical velocity of the rifles out of the box
is 450-500 in .22 and 550-600 in .177. Of course you may find some
that vary from this but quality control is not a strong point of the
less expensive Chinese airguns. It is a simple rifle that is easy to
work on, responds well to tuning, and is very accurate. The only
complaints I have about this rifle concern the trigger spring and
cocking arm latch which are prone to breakage over time.
The following pictures illustrate some key areas that help to identify the B-3 rifle. The rifle featured below is a late model variant with the cleaner woodgrain and finish and black mainspring guide. Note that the stock was not relieved where the trigger guard is fitted as it is with the B-4 rifle. The rear sight it ahead of the loading port and is spot welded to the receiver while the front sight is simply pinned to a turned-down section of the barrel.
You can basically break the B-3 into two categories, early model or late model. The late model rifles are preferable as the finish and assembly tends to be better, there is less wood filler on the stocks, and the improved spring guide is both stronger and shorter which allows for installation of a larger mainspring. It is easily identified by the white spacer found between the stock and butt of the rifle and the spring guide is typically black as opposed to the early model which is white.
Some of the options that have been used in tuning the B-3 include basic cleaning and lubrication, leather seal improvement, synthetic seal retrofit, B-4 spring upgrade, piston stroke modification, and transfer port tuning. I will try to touch on each of these as this guide progresses.
There are many options when it comes to enhancing the looks of your B-3. Some modifications not only improve it's looks but also improve other aspects of the rifle's performance. Some of these include shortening the barrel, installing a muzzle brake, shortening the cocking arm, refinishing or painting the stock, coating the stock with bedliner (as was done in the example picture on the first page), and many more. You are only limited by your imagination. I will try to address the bedliner application and cocking arm modification later in this guide.
Before getting into the steps involved I feel it may be best to cover a few thing that will help you avoid trouble.
The trigger group on this rifle uses several pins as pivots for items like the sear, trigger, and anti-beartrap mechanism. These pins are held in place by the stock so care must be taken during stock removal to avoid having these pins fall out. The best method for preventing this is to avoid having the rifle on it's side when you remove the stock. I usually lay mine on it's back so that I have access to the underside and have found that this works best.
The spring is under substantial load when installed in this rifle. Although I am able to remove the spring without a compressor, I would advise against it. A spring compressor should be used every time you tear down your B-3 as it prevents damage to the rifle as well as yourself
Moly (as in moly paste or lube) is harmful and should not be allowed to contact your skin. I suggest using latex gloves to avoid this and make cleaning up easier.
ALWAYS hold the cocking arm when the chamber is open, ALWAYS have the stock installed when testing the cocking action, and ALWAYS try to avoid having your hand between the cocking arm and the barrel with the rifle cocked. It only takes on incident to hurt yourself badly and injuries can include loss of limbs and broken bones so don't take these lightly.
are several ways to go about tearing down the B-3
rifle but I have tried to lay this out in a way that will assist
those who are doing this for the first time. As you gain experience
with your B-3, you may find your own way of doing things. Until then,
this will help you get the job done.
I must assume that you have a spring compressor and some mechanical aptitude otherwise you wouldn't be trying this. If you require a hospital visit after installing a light bulb, this probably isn't a great idea.
I am sure this will be overly simplified for many but it may prove useful to those who are just getting started in this hobby.
Barrel-the portion of the rifle through which the pellet travels after firing
Muzzle-the portion of the barrel where the pellet exits
Receiver-the portion of the rifle that the barrel attaches to, contains all internal parts
Cocking arm/lever-lever that you actuate to cock the rifle
Cocking link-connects the cocking arm/lever to the chamber
Chamber-the area where compression takes place, piston slides within
Piston seal-seals piston to chamber in order to compress air, leather or synthetic
Piston-powered directly by mainspring, slides within chamber to compress air
Mainspring-spring that drives piston forward upon firing
Spring guide-secures spring within receiver, stabilizes spring to avoid canting
Trigger-stamped steel lever that actuates firing
Sear-locks piston in rearward position during cocking and releases piston during firing when actuated by trigger
Trigger spring-connects trigger to sear
Anti-bear trap-prevents trigger movement when cocking lever is in the fully cocked position
Expansion washer-found within leather piston seal, helps seal maintain shape and helps to secure it to the piston
Breach-portion of the barrel where the pellet is inserted
Breach seal-seals chamber to the portion of the barrel where the pellet is inserted
Transfer port-orifice in chamber that air passes through before contacting pellet
Stock-the big wood thing
Butt-your sitting on it
With the rifle sitting on it's back, remove both front stock screws and the rear trigger guard screw before removing the stock. Work slowly and watch for loose trigger pins.
Remove trigger pins and set aside. The sear pin uses e-clips to retain it so carefully remove the e-clip from one side of the pin and slide the pin out. Do not remove trigger spring from sear/spring assembly. Doing so can cause premature spring failure and is not needed to service this rifle. Note: the sear pin, sear, trigger, and trigger spring can remain in place during tear down if desired. Be sure they are kept out of the way while servicing the remainder of the rifle.
Remove the anti-bear trap spring assembly ( just ahead of the trigger group) by removing one retaining screw. Leave screw in the spring retainer to keep the springs in place. The rest of the mechanism can remain in place at this time. This step is optional since the cocking link can be removed by extending the anti-bear trap springs and relieving pressure against the link.
Unlatch the cocking arm and unscrew the pivot pin/front sling swivel. With the pivot pin removed, rotate the cocking arm and link away from the barrel until it releases from the chamber. Once the cocking arm and link are removed, set aside the anti-bear trap.
Remove the plastic end cap at the rear of the receiver. Using a spring compressor, depress the spring guide into the receiver and drive out the guide retaining pin. Slowly release spring tension with the compressor.
Remove the rifle from the compressor, the guide from the spring, spring from the piston, and then slide the chamber/piston assembly out of the receiver.
Remove the piston from the chamber by pulling gently. Avoid catching the leather seal on the cocking slot in the chamber.
Remove the piston seal retaining screw and then the expansion washer from the seal
To reassemble the rifle, reverse the steps above making
sure to apply blue threadlock to all screw threads, especially the
piston seal retaining screw. The illustrations above show the correct
order of parts installation.
The focus of this tune is to smooth the action of this rifle and gain a small amount of power in the process. Most of your time will be spent eliminating any areas within the action that might create excessive friction between the moving parts. I will describe the process by breaking it down by individual parts. A thorough cleaning should be done both before and after all polishing or sanding.
Using sandpaper wrapped around a wooden dowel, smooth the
inner surface of the tube. Pay close attention to the areas that have
been spot welded and the opening where the sear protrudes. Any area
that might catch on the chamber or piston needs to be smoothed.
Also take a piece of sandpaper and round off the edges of the loading port to. Start with a course paper ad work your way to a finer grit as you progress. Some minor sanding marks in the surface are fine and will help to hold any lubricant in place. Also smooth the edges of the opening that the cocking link enters.
Lubricate the interior of the receiver with a light film of moly paste being sure not to get any on the trigger or sear. Do not lubricate the end of the receiver where the barrel enters.
Using sandpaper, smooth out the front and rear edges on the
outside of both ends. You want to eliminate sharp edges that may gouge
the inside of the receiver as it travels during cocking. Also round off
the edges of the opening that the cocking link hooks into.
Using an automotive brake hone and a drill, hone the inside of the chamber until the surface is uniform and as smooth as possible. If you plan on installing a synthetic seal, leave a slight crosshatch. If you are retaining the leather seal, get the surface as smooth as possible and then follow up with a very fine sand paper.
Lubricate the interior of the chamber with a very thin film of silicone grease (dielectric grease). Do not lubricate the exterior.
Using sandpaper, round off the front edges of the piston
behind where the seal seats and the opening that the spring enters. You
want to be sure that the front edge of the piston will not gouge the
chamber as it travels forward during firing and that the rear will not
gouge the receiver as it is cocked. Also use the sandpaper to smooth
out any weld marks and to soften the edges of the cocking groove.
Polish the indentation that the sear engages when cocked. Don't change
the angle or shape of the indentation but simply smooth the surface.
This will improve trigger feel.
Lubricate the exterior of the piston with a light film of silicone grease. Do not apply grease to the indentation that the sear engages.
Use a fine stone or sandpaper to polish the spring ends. Also
round off the cut edges of the end coils to keep them from digging into
the piston or spring guide. Inspect the spring for canting. If the
spring has serious canting then it is best to replace it.
Lubricate the ends of the spring with a small amount of moly paste. If using spring tar, apply it lightly to the exterior of the coils except where you have applied the moly paste at the ends. If you aren't using spring tar, apply a light film of moly paste to the exterior of all spring coils.
Remove and molding seams from the guide where the end of the
spring will seat. The spring should be able to rotate as freely as
possible on this surface.
Lubricate any guide surfaces that contact the spring with a light film of moly paste.
Smooth all areas that contact the receiver or chamber using
sandpaper. Do not alter the shape of the hook that engages the chamber.
Apply a light film of moly paste on the portion of the cocking link that makes contact with the groove in the receiver.
Leather piston seal
Remove expansion washer and retaining screw from seal,
degrease it using automotive brake clean or preferred cleaner, scuff
exterior surfaces with sandpaper to raise a slight nap, then soak seal
in leather conditioning oil for approx. 15 minutes. Once seal has been
cleaned and soaked, knead the seal with your fingers while adding oil
as needed until it is pliable but not too soft. Once this is done dry
the seal using paper towels until it is just slightly moist to the
No further lubrication is needed.
Inspect this seal for cracks or other irregularities that may
prevent it from sealing. If the seal is not in good condition you will
have to replace it. Replacing this seal is as simple as pulling out the
old one and pressing in the new one. Sometimes the old ones are rather
hard and don't want to cooperate but it will come out. The QF2 cleaning
kit contains 2 new seals that will fit this rifle. See the section on
upgrading to the QF2 mainspring for more details on this kit.
No lubrication is needed.
Use a length of nylon trimmer or “weedwacker” line to pull
through a few cloth patches saturated with “Goof off” followed by dry
patches. Repeat this until the patches come out of the barrel clean. DO
NOT USE bore brushes or metal cleaning rods or damage to rifling within
the barrel may occur.
No lubrication is needed.
the basic lube tune, this has to be one of the
better modifications you can perform on your B-3. The QF2 spring is
found in the QF2 cleaning kit that is available online from retailers
It not only includes the spring but also includes 2 breach seals, a
new sear, and a synthetic piston seal. The piston seal will need to
be adapted if you wish to use it and the included oil and cleaning
rods shouldn't be used on any airgun you cherish. Those of you who
have the late model version of the B-3 with the black spring guide
have it easy. Those with the earlier white guide will have a little
work ahead of you.
With the black spring guide, the QF2 spring is a perfect fit and requires no modifications. If you have the white guide, you will have to cut back the area of the guide where the spring seats until it matches the dimensions above. The distance from the center of the retaining pin hole to the end of the spring seat must be no longer than 1.640 inches. A little shorter is actually better as it allows more freedom for you to pre-load the spring on the piston end. The new spring should be lubricated as outlined in the “Basic lube tune” section before installation.
What to expect. Cocking effort will increase very slightly, velocity can increase anywhere from 50-100 fps depending on your rifle, and the rifle will be much smoother to cock and fire. Installing the spring will take a bit more effort as it is stronger and longer than the original so be sure that your spring compressor is up to the task.
B-3 black guide
the mainspring is the act of inserting
spacers between the spring and piston to decrease the spring's
installed height. Adding pre-load can increase velocity and smooth
out the rifle sometimes but it needs to be done cautiously as it can
also cause damage to the spring or prevent the rifle from cocking.
People often use metal washers inside the piston where the spring
seats to add pr-load and weight. Adding weight can also add power
sometimes but adding too much will cause piston slam. Piston slam is
when the momentum of the piston moving forward overcomes the
resistance of the pellet in the barrel causing the end of the piston
to slam into the end of the chamber. This will send a shock through
the spring and into the plastic guide and can cause them to fail. For
those who wish to tune without adding much weight, ½ inch
nylon faucet washers found in hardware or home improvement stores
work nicely. Each washer is approx. 1/8 inch thick and adds little
Three lubricated nylon washers installed in a B-3 piston.
I've found that an unmodified B-3 with the stock spring
can usually run 3/8 inch of pre-load without binding the spring and
often provides good results. If you want to try adding weight,
pennies make a good testing medium and can be used in conjunction
with the faucet washers. Any washers or spacers that are installed
between the spring and piston should be lubricated with a small
amount of moly paste.
Many people choose to keep the leather seal that the B-3 came with but wish it could seal a little better. This modification will improve the leather seals ability to do it's job and will make it's diameter adjustable so it can be fitted to the chamber better.
You will need two 3/8 inch faucet washers and one ½ inch faucet washer. Remove the retaining screw and original expansion washer from the seal. Remove the retaining screw from the expansion washer and then install the ½ inch faucet washer followed by the two 3/8 inch faucet washers. Install the new assembly into the seal, apply blue threadlock to the retaining screw threads, and install assembly onto the piston. The tighter you turn the screw, the larger the mouth of the seal becomes. Adjust is so that there is a light amount of drag when the piston is moved within the cylinder.
washer, modded expansion washer, leather seal
The B3 - for all its charm - does come standard with something no air rifle deserves to be afflicted with. A stamped iron front sight that is riveted and cross-pinned to a turned-down section of the muzzle. Out of the box, my B3's front sight had a deformed hood, probably from sliding around unsecured in its box during shipment. The iron sights worked, no question, but they were also the most hideous things I'd ever seen. So when I came across a scope at the local sporting goods store, I figured it was time to get rid of the 'cancerous mole' - the front sight.
After grinding down the rivets, punching out the retaining pin, and prying the front sight assembly loose, I found that the turned down section of the muzzle was almost as ugly. It was mostly bare metal, but had picked up some blueing in certain areas. There was even more of that wok oil in the small ridges of this section. I suppose I should have cut it off, but then I would probably not be writing this article.
Figure 1 shows the basic diagram of the muzzle brake assembly and also the parts that are involved. Itemized list follows:
The 1/2 inch hose sleeve is a modified piece of hose. It was originally
"RV water hose" at the "mart of wal". This has 2 layers - a clear outer
layer and a white
inner sleeve. These layers are separated by criss-crossed fiberglass
threads. If you
have seen it, you know what I'm talking about. It might also be
marketed as 1/2 inch
garden hose. The inner sleeve is what should be used. Discard the outer
layer and the glass threads.
1. Prepare the muzzle. Make sure it is clean and free of oil or grease. Slip the hose sleeve onto the turned down section as far as it will go. It will be a tight fit because the muzzle is a tad larger than 1/2 inch.
2. Prepare the muzzle brake body. Cut the threaded sections off of the PVC pipe nipple. Keep one of the cut off sections. This will be the mold for the plug.
3. Slide the PVC piece onto the muzzle. The sleeve will make it a very tight fit. I sprayed a little WD-40 on the sleeve to help slide it on. The WD-40 evaporates and the PVC piece stays put.
4. Making the plug.
As it turns out, the head of a 1/4 inch carriage bolt fits inside a 1/2 inch PVC nipple. It's a bit loose, but not so much that it's unacceptable. The length of the carriage bolt isn't super critical as long as the smooth section is making contact with the the JB weld. Drill a 1/4 inch hole in a wood block for the carriage bolt to go through. Put a lump of JB weld in the mold and push the carriage bolt down to form it into shape. It might make things easier if you polish the carriage bolt with auto wax before using it. I didn't, so it's not disastrous, but in hindsight, I think I should have waxed the bolt to make release a little easier.
5. Install the plug. It may take some persuasion, but once the JB weld has hardened, it can be removed from the mold. This plug should now be installed into the muzzle brake body. It will probably look a little rough, but don't worry, JB weld is sandable.
6. Finishing. Once the plug is installed, drill into it and put in the set screw. I don't have access to any fancy screws so I just countersunk a small metal screw into the plug. This keeps it in place while the face is sanded into an acceptable finish. I used a sanding block with 120 grit, then 220, then finished with 320. Use a 1/4 inch drill bit in the muzzle brake exit to widen the hole a bit, and adjust the hole if it seems off center. Paint the entire assembly your choice of color. Black seems to work nicely, but if your personality/creativity calls for something else, feel free to take this opportunity to express yourself.
That's all I have for now. As always, be safe and have
Mainspring bearing surfaces