Tuning Guide
Hercules/Cummins B-3 Rifle
By: R. Sauer & V. Palitang


Tuned B-3 featuring original stock finish and a Powerline 3-9x32 scope. Note that white spacer has been removed from the butt.
 
See RSE Performance Airguns for fully tuned B3-2's

 


Index

Copywrite and contacts
   R. Sauer
    V. Palitang

Introduction to the B-3 rifle
    Introduction
    Identifying the B-3 features
    B-3 variants
    Tuning options
    Appearance options
    Warnings

Tear down procedure
    Introduction
    Parts descriptions
    Procedure

Basic Lube Tune
    Introduction
    Procedure

QF2 mainspring upgrade
    Mainspring dimensions
    B-3 Mainspring
    QF2/B4 Mainspring

Mainspring pre-load and piston weighting

Leather seal expansion washer improvement
    Introduction
    Procedure

Making a muzzle brake for the B3
    Introduction
    Basic design
    Procedure

Mainspring bearing surfaces
    Introduction
    Procedure
    Dimensions

Bed-liner stock coating
    Introduction
    Procedure


 All text and images contained within are the sole property of their authors. Reproduction and/or modification in part or in whole is prohibited without specific written consent of the authors.
Questions or comments can be mailed to...
Russell S. Sauer guru1@charter.net
Virgil S. Palitang vspalitang@yahoo.com

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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.

Identifying B-3 features

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.


B-3 front sight



B-3 rear sight



B-3 trigger (note that trigger is 2 piece sheetmetal unlike milled B-4 trigger)



Typical late model B-3 grain pattern



Variants

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.

Tuning options

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.

Appearance options

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.

Warnings

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.

  1. 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

  2. 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.

  3. 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.

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Tear down procedure

Introduction

There 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.

Parts

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.

  1. Barrel-the portion of the rifle through which the pellet travels after firing

  2. Muzzle-the portion of the barrel where the pellet exits

  3. Receiver-the portion of the rifle that the barrel attaches to, contains all internal parts

  4. Cocking arm/lever-lever that you actuate to cock the rifle

  5. Cocking link-connects the cocking arm/lever to the chamber

  6. Chamber-the area where compression takes place, piston slides within

  7. Piston seal-seals piston to chamber in order to compress air, leather or synthetic

  8. Piston-powered directly by mainspring, slides within chamber to compress air

  9. Mainspring-spring that drives piston forward upon firing

  10. Spring guide-secures spring within receiver, stabilizes spring to avoid canting

  11. Trigger-stamped steel lever that actuates firing

  12. Sear-locks piston in rearward position during cocking and releases piston during firing when actuated by trigger

  13. Trigger spring-connects trigger to sear

  14. Anti-bear trap-prevents trigger movement when cocking lever is in the fully cocked position

  15. Expansion washer-found within leather piston seal, helps seal maintain shape and helps to secure it to the piston

  16. Breach-portion of the barrel where the pellet is inserted

  17. Breach seal-seals chamber to the portion of the barrel where the pellet is inserted

  18. Transfer port-orifice in chamber that air passes through before contacting pellet

  19. Stock-the big wood thing

  20. Butt-your sitting on it










 



  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Remove the piston from the chamber by pulling gently. Avoid catching the leather seal on the cocking slot in the chamber.

  8. 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.

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Basic lube tune

Introduction

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.

Procedure

  1. Receiver

    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.

  2. Chamber

    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.

  3. Piston

    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.

  4. Main spring

    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.

  5. Spring guide

    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.

  6. Cocking link

    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.

  7. 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 touch.
    No further lubrication is needed.

  8. Breach seal

    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.

  9. Barrel

    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.

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QF2 mainspring upgrade

Introduction

Besides 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 like www.southsummit.com. 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.

Procedure

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 with dimensions


Mainspring dimensions

For those who may be interested in finding alternative springs for the B-3, I have provided the specifications below. These dimensions are correct at the time of this writing. Due to production variations, your dimensions may vary slightly from what is listed.

B-3 mainspring
QF2/B4 mainspring
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Mainspring pre-load and piston weighting

Pre-loading 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 weight.

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.

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Leather seal expansion washer improvement

Introduction

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.

Procedure

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.

Original expansion washer, modded expansion washer, leather seal


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Making a muzzle brake for the B3

By Virgil S. Palitang

Introduction

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.

Basic design


Figure 1. Muzzle brake diagram. Not to scale

Figure 1 shows the basic diagram of the muzzle brake assembly and also the parts that are involved. Itemized list follows:

Important note: The 1/2 inch hose sleeve is a modified piece of hose. It was originally labeled "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.

Procedure

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.


Figure 2. Plug mold diagram. Not to scale.

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 fun!

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Mainspring bearing surfaces

Introduction

Due to it's very nature, a coil spring will twist during compression and expansion. In most applications this isn't much of an issue however, due to the length of the spring and the requirements we have for our airguns, this can present a problem when it comes to shooting. If spring twist is not controlled during the firing cycle, the rifle will produce substantial recoil which can effect accuracy. Since we can not eliminate this twisting action we must learn to control it. The goal of this modification is to install lubricated bearing surfaces between the mainspring and the remainder of the airgun action. This allows the spring to rotate independently in relation to the rest of the gun and may provide reduced recoil, higher velocity, and a quieter spring action. This procedure will add a minor amount of spring pre-load which must be taken into consideration in order to avoid coil bind.

Procedure

You will need to find two metal washers, one for the piston end of the spring and the other for the guide end. Although I have been unable to find washers which fit without modification, adjusting their size is relatively easy with a little mechanical inclination. The approximate washer dimension required are listed below.

Piston end
    Thickness=.075
    Outter diameter=.790
    Inner diameter= no specification required

Guide end
    Thickness=.075
    Outter diameter=.790
    Inner diameter=.470

The piston end must have an external diameter that allows it to fit inside of the piston and rotate freely. Thickness and internal diameter on not important here however, thickness will effect mainspring pre-load.
The guide end must have an internal diameter that allows it to slip over the guide shaft and rotate freely. The external diameter must be small enough to allow it to fit within the receiver without interfering with normal movement of the piston. The dimensions provided should work with most B-3 rifles. Once again, the thickness is only important in that it will effect spring pre-load.
Once you have the correct washer dimensions it is important that all surfaces be polished in order to reduce friction. A fine sandpaper will handle this nicely.

With properly sized and polished washers, apply a slight amount of moly on both sides and install them in their respective positions. Reinstall the mainspring and assemble rifle as normal. If, after assembly, the rifle will not cock fully then you have either coil bound the spring or the rear guide is too large and is preventing the piston from moving rearward enough to engage the sear. On an otherwise stock gun, coil bind should not be an issue as it can use approx. 3/8 inch of pre-load safely.

Note that metal washers are not required if suitable synthetic versions can be found. Normally I would suggest using synthetics at the piston end to avoid adding too much weight to the piston. When using synthetic washers, it is best to use two washers back to back per spring end to keep friction to a minimum. Doing this increases our pre-load more than the other options but can produce excelent results. Treat synthetic washers the same as metal ones as far as dimensions and lubrication are concerned.

Black B-3 guide with lubed metal washer installed


B-3 piston with lubed synthetic washers. Note that two are required when using synthetic washers.



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Bed-liner stock coating

Introduction

One of the biggest complaints concerning many of the Chinese manufactured airguns is the poor finish quality of the stock. The stock is often dipped in a stain/varnish mix and allowed to drip dry which leaves clouding, runs, and no hint of any grain at all. The unfortunate thing in many cases is that once stripped of this varnish, we find that the wood isn't exactly pretty. Another issue we encounter is the fact that the bedding is routed after the varnish has been applied which means that the bedding area is not protected from moisture. For those who use their rifles outside, this is a problem.
For those who have found their stock in too poor a condition to refinish or who simply don't care to go through the effort, the bed-liner option is quite appealing. It offers both the look and texture of a synthetic stock as well as excelent protection against the elements. Mine make trips through the woods very often and the coating manages to stand up to briars and anything else that I have thrown at it.
The following is the procedure I have used that I find obtains the best results.

B-3 stock finish showing exposed bedding area



Procedure

The only product I have tried so far has been the Dupli-Color brand of Truck Bed Coating. It has never given me any problems and it is readily available so I have had no reason to try other brands. Based on this fact, I can't speak for the results or techniques that might apply to other products. I would assume that the results would be the same with this technique but to do so is at your own risk.

B4 stock which has been scuffed as mentioned above

B-3 stock after bed-liner coating showing the protected bedding area



This illustrates the bed-liner texture after applying 3 coats



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