Fixing scope rail

If you have purchased scope-rail from here http://target-tune.in/international/products/IHP-scope-mount.html then follow this DYI

This is all what you need Yes screw and drill machine is not shown here. Just follow the picture.

Place the rail (the side marked in red) as shown in the picture:

for 4mm Tap you need 3.2mm drill

Once done, dismantle (You can use the following link) the gun.  File off and wash out  unnecessary material. Assemble them back. Once done, use the screw to fix the rail, check if you can cock. If not remove the screw which is located towards the back sight file off a little (say 1mm) and screw it back. You should be able to cock now.

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Tuning HW30s or R7 Part- II Problem Identification

Ok! Now we are going to understand what needs to be look at. And why it is required to tune.

Lets follow the picture.

Here we are going to remove the cocking arm. There are two pin that needs to be removed in order to remove the required piece. There is another way too. By removing the main screw that holds the barrel with the receiver can be removed too. But this is simple way.

The next pin too has to be removed.

Now you see the cocking arm is removed. Interestingly if you

Closely, the surface of the receiver badly damaged.

Also see the cocking arm link. Bad in shape. That means metal to metal friction was heavy. So we have to reduce the excess material from the link and polish it. Also we have to File-off few micron of material from the receiver and then polish and blue them.

Not bad after bluing.

It is important to deburr carefully the arrow marked areas. While doing that, just keep in mind, while you will enter the seal, it may cut. So you have to remove all that possibly can cut the seal.

Also you see, the receiver is honed. The ID was Phospheted  from factory to avoid rusting. But it will also avoid nicely lube that important for seal.  Don’t worry about the rust. Go ahead and  hone the receiver with 320 girt if you are doing it with low speed. If you are good with hand tool you can go with high speed honing and in that case, 220 grit will do wonderful job. If you don’t have your hand on water soluble lard oil you can use singer oil for honing.

I have made a honing tool something like this. I wrap emery paper around the front part. The slit helps to secure the paper around it.

See how the deburring and honing is done. Some says they do mirror polish. I strongly object that. My suggestion, a fine Matt finishing is needed for an airgun. 

You are done with your receiver.

In next part, will talk about the spring, piston and the seal and of-course Lubricants.

 

Tuning HW30s or R7 Part- I Dis-assembly

After the receiver removed from the furniture these are the list of job you got to do. Just follow the Picture tutorial.

To remove the dowel pin, make sure you are using wooden hammer or plastic hammer like the one is visible in the picture.

Congratulation. You have completed a difficult task.

Next: In Part – II will discuss about what to clean.

How to Torture the Spring Guide?

The is very common in HW Spring guide. Is there anything wrong with the material? NO.

If you see closely, the material is cast Nylon 6 and the property below:

  • High modulus
  • Low stress
  • Good dimensional stability
  • Non galling
  • High fatigue resistance
  • Abrasion resistant
  • Low coefficient of friction
  • Vibration and peening resistance

But surely something is wrong with the fitment and balance between the steel ring and the guide; thus the 800 newton gives unprecedented off-axial force on the ring and you will have this result.

Good that they have used Cast Nylon . If they would have used Delrin the result could have been a disaster. Because delrin cannot take this much abuse.

Let me show you an example:

A customer purchased one of our Gamo tune kits and he decided to use a spring from a different source. He requested us to make the spring guide as per his requirement. He shared the dimension of the spring. After analysis, we had suggested what the OD of the spring guide should be. However, he wanted a much  bigger OD than that in our recommendation.

We supplied the tune kit together with  caveat that a bigger OD may cause that the guide to be tortured heavily. The customer informed us later that using bigger OD resulted in what we anticipated and warned against:

Lets see what might go wrong here.

1) Delrin is not like cast Nylon. It breaks.

2) If you see the broken part, left end, it looks like it is uprooted and it can happen only when the force acted somewhere middle of the guide heavily

This can happen only when the guide is too tight for the spring or the spring is not evenly coiled. And top of that, there is another possibility that can support this would be, the spring end was not grounded properly which led to the breakage of some part from the neck.

Anyway, the good news is: Globally we have a few hundred customers. But only one customer had this issue.

Interestingly, this customer, purchased the product on 3rd December, 2010 and after one year he came back to us and demanding for a REPLACEMENT!!

And top of that, he is kind of blackmailing by saying if we do not fulfill his demand, he will tarnish our company’s reputation.

We think, this demand is unreasonable on his part. We are sure you would find this unreasonable too.

If anyone is interested to read about his complain we found the link of the customer and here it is.

http://bsaog.co.uk/forum/index.php?PHPSESSID=b57702e19435f08df0b1fde5d119849a&topic=36073.msg316151#msg316151

Reason to change Spring guide for HW30

This is what you usually cannot see with naked eyes.

In the picture below, you see on the original (OEM) spring guide hof HW30 showing some bucking.

The reason is very simple. The OEM spring guide is way below the required OD size for the spring.

Secondly, the Material that used for the guide is not strong enough to hold the power of the spring.

 

This picture shows the custom made spring guide.

No bucking observed. Alignment of the tophat is not inline with the guide thus the little difference you see down there.

 

 

Reason to change Spring guide for HW30

This is what you usually cannot see with naked eyes.

In the picture below, you see on the original (OEM) spring guide hof HW30 showing some bucking.

The reason is very simple. The OEM spring guide is way below the required OD size for the spring.

Secondly, the Material that used for the guide is not strong enough to hold the power of the spring.

This picture shows the custom made spring guide.

No bucking observed. Alignment of the tophat is not inline with the guide thus the little difference you see down there.

Understanding Airgun Spring -Part1

Spring! A simple word but not that simple a subject.

The intention of this post is to enlighten fellow “air gunners” looking at spring replacements for their air rifles to better understand some basic technicalities of springs while selecting the same.

To start with, let us study 3 different springs. For a slightly in-depth understanding, we will look at their chemical compositions and manufacturing processes as well.

Spring used for sock absorber

Spring used for shock absorber

shock absorber spring -close-up

A closer look at the surface of this spring reveals a quiet uneven and rough surface. Unfortunately, an untrained eye will not be able to pick the difference as these very springs, when they hit the market are usually polished. The spring steel used in these types of springs is usually cheap and has carbon content of between 0.50% to 0.80%. These springs also have a different drawn process compared to springs that are fit for Air Guns. The spring wire being perfectly round in these springs is questionable. These springs are also not capable of taking high stress, and therefore on load, it will set very quickly.

Carbon content is not the only factor that plays a roll in making spring steel better or worse. Percentages of Mn, Si, P, S, Cr and V are also very vital to the end result of the spring steel quality. A simple difference between high tensile steel and low tensile steel boils down to stringent quality control on the ratio of the above said chemicals and a “better drawn” process.

Furnished below is the drawn process:

For general shock absorber spring:

  • Wire Rod
  • Heat Treatment
  • Pickling –> Wikipedia
  • Drawing
  • Oil Treatment
  • Inspection
  • Wire Forming

In addition to the above, for a good Air Gun Spring, the following additional processes is introduced after Drawing.

  • Heat Treatment
  • Pickling
  • Drawing

The picture below shows a spring made from good quality steel using the above 10 steps of the drawn process with the right quantum of carbon and other chemicals mentioned earlier. This is very evident when one closely inspects the surface (Please compare the previous photographs and the ones below).

  • Airgun Spring

Airgun Spring -Close

Even if both the spring steel were to go through the same 10 steps in the manufacturing process mentioned above, the low carbon steel spring cannot attain the same smoothness as the high carbon steel. This is because there is a tight bonding between the metal and carbon.

In addition, elasticity can be increased in a good spring wire through a process called low temperature annealing. Most spring maker are either not aware of this process or choose to avoid it due to the high costs involved and the resultant increase in production cost.

Left -Shock absorber; Right - Airgun Spring

A comparison of the two spring steel quality side by side:

Close-up

Air gun springs available in the country are made from Shock absorver grade steel (seen on the left). This is largely due to the manufacturers lack of knowledge in spring engineering.  It is not uncommon to hear praises for springs like Cherokee, G Smith and many unknown brands for their quality. I have closely inspected these springs and they tell a different story. I have found all equally bad! I have heard people say that during installation these springs are extremely hard to install and later they become soft or slack. One thing is for sure. A good spring never changes its state so quickly.

There is a misconception among many air gunners that the hardness of a spring is directionally proportional to its power potential. “The harder it is, the better the spring will be”.

Please click on the following link to get an idea of what I’m trying to convey and for an idea of Plasticity (I do not wish to go in detail on this topic). http://en.wikipedia.org/wiki/Plasticity_(physics)

The third spring is good for working under high temperatures, and has a different chemical composition and manufacturing process and is usually very expensive. Due to high resistance of fatigue under high temperatures, this spring will last very long. The surface is smooth and very similar to the air gun spring we studied earlier, and is hard to differentiate with the naked eye!

That’s all for now folks!

Hope this little article helps you in choosing the right spring for your baby.

P.S: Part II will give more dept…..

Springs for BAM B40

Let me share some technical details:

Piston ID: 21.25mm

Guide ID: 12.93mm

Allowable Solid height of spring: 96.28 mm (I will discuss Solid height and allowable solid height in another post)

Considering the Spring guide ID, a supplier of mine has sent me a spring whose spec is as follows:

Wire ID: 3.048mm

Coil ID : 13.43

Number of Coil: 31.5 and almost 10 inch long

Seems to be a good fit for the spring ID and very easy to cock the gun.

I was trying to insert it inside the gun…and oops…very hard. I could not do it by hand. Like most GAMO’s, the B40 has almost nil preload length and you don’t need a spring compressor to dismantle the gun. The spring was hard because the spring was not set.  So I decided to SET the spring by using a spring compressor.

This is what I did. I inserted the spring in a tube and then inserted a rod almost the same size as spring ID behind the spring and put them under compression, in solid height state for almost an hour.

The picture below shows the spring under compression.

Spring Compressor

Spring under compresson

Once the spring was removed from compressor chamber, I found the spring reduced by 20%. This is absolutely normal!! If you do not preset and try to inset the spring directly in to the gun, there is a high chance of accidents, and moreover greater chance of structural defect of the spring. Therefore “setting” spring is very important and has to be done very carefully.

After setting the spring, I found it  is very easy to assemble the gun. Once assembled, I found the gun to be very easy to cock and very less recoil. And power??? Yes the power has increased. 

The picture below shows the impact.

On wall from 8 meters

On wall from 8 meters--Closeup

Yes, that’s true; the pellet is IN a wall made of solid concrete. BAM!!!

21.25

Main Spring Busted

It was two weeks ago. A few of us went plinking and the agenda for the day was “shoot, shoot and shoot” 🙂 . After a lot of casual pinking came the serious part. I was very determined to hit the bulls eye and at a very descent distance. I leveled my rifle….set my sights….was very confident that the result of this shot would be the bench mark to follow for the day. As I squeezed the trigger, apart from my finger, my whole body froze momentarily to ensure the least possible deviation of my aim and ……Bang!!! A loud noise from my gun just like a .22 hornet. That wasn’t right. I knew it was not supposed to sound like that. I instantly knew for sure that this sound spelt bad news. This bang was very abnormal unlike the others before it. Everyone’s face turned to me with a big question mark. On opening the breech area of the BAM B40, the rifle in question, I found the pellet stuck close to the breech washer which caused a blank fire. Intriguing indeed! I still don’t have a clue how on earth this happened.

After removing the pellet, I went ahead and shot a few more rounds. I noticed that the firing cycle not as smooth as it was earlier. While cocking the gun, one thing was obvious. While pulling the under lever to cock the gun, the immediate resistance had reduced by about 3 to 4 inch. I could also feel some metal friction. It dawned on me that the only explanation to this sound was a broken spring. What was interesting however was that the Point of Impact of the pellet had not changed.

Back home and a week later, I at last fond time to dismantle the gun over the weekend. And yes, exactly what I thought. The spring was busted. What surprised me though was that the spring wire was fat and one could never have guessed that one blank shot could have caused this. Perhaps the spring was highly stressed due to buckling as the stock guide was not a good fit for the spring (please refer to the topic “Spring Guide! What is it” for a better understanding on this subject), or the stress was not properly removed during the spring manufacturing process.

Spring Busted

The Seal seemed to be okay. Not a single scratch could be found.

Seal Profile view

I have now replaced the seal with an Apex seal but could not find a replacement stock spring. I’ll soon have one custom made for a perfect fit. The existing stock spring has a 3.32mm wire dia. The spring I have designed will have a 3.2mm dia to get more tensile strength while simultaneously softening the cocking effort.

How to remove rust

This is what I am going to restore.

Rusted object

Rusted Object Anothe view

Now going to Add Cooking salt 1 spoon in a mug filled with water so much so that the object submerged it fully. Then I add equal amount of vinegar. Mix it well and the put the object.

Salt

Vinegar

submerged in water

Keep it for 1 hr. and then remove it and then wipe it off with a wet cloth. See the result..

Rust is removed

Rust removed