Resealing the Crosman 38T target revolver: Part 5

by Tom Gaylord
Writing as B.B. Pelletier

38T
Crosman 38T.

Part 1
Part 2
Part 3
Grips & tips
Part 4

History of airguns

Today we have another guest blog by reader Ian McKee who we call 45Bravo. He shows us how to reseal a Crosman 38T revolver. The revolver he reseals is the same .22 that I am about to test for you and also the same gun whose grips he fixed for us, so I linked to all the previous Crosman 38T links, because this is a large series.

If you’d like to write a guest post for this blog, please email me at [email protected].

Take it away, 45Bravo.

Resealing the Crosman 38T target revolver

Resealing the Crosman 38TThis report covers:

This report covers:

  • Start
  • Disassembly
  • The seal kit
  • The piercing assembly
  • The tube assembly
  • The valve group
  • Assembly
  • Hammer and trigger assembly
  • The valve group
  • The barrel and shroud

The 38T is a vintage all-metal (except the grips, rear sight, and the rotating pellet cylinder) CO2 replica revolver that closely mirrors the lines and grip of a 1980’s Smith & Wesson revolver. 

In the firearm world, most revolvers are considered a simple design, and they do have relatively few parts.  But when you make a airgun replica of a firearm, you have to work within the envelope (profile and dimensions) of the original. 

That means you have to get creative with your engineering and layout as to where you can place your necessary components such as the CO2 cartridge, the valve, and the way to feed the intended projectiles. Typically, on a piece-by-piece count, an airgun will have more internal parts than its firearm twin. Today we look at such an animal.  

I apologize in advance that it is a long blog, but there are a lot of steps to cover.

Start

Start by removing the grips, the right grip is held in place by 2 screws, the shorter one of the 2 goes in the top of the grip, the longer screw goes in the bottom. The left grip is held in place by a spring clip that attaches to the CO2 cartridge, so the grip will not stay in place unless a CO2 cartridge is in the gun.  Remove the left grip, and then unscrew the CO2 cartridge piercing screw, and remove the cartridge.

TIP:  I would suggest leaving a cartridge in the gun, but not pressed into the CO2 face seal. Just tight enough to hold the grip in place.  You sometimes see these pistols listed for sale without the left grip as it has become lost over the years. 

These grips are thin, and tend to break and crack around the alignment pins and also where the CO2 clip is attached. The gun I’m resealing had those issues, and the repair has been covered in the GRIPS & TIPS BLOG.

Phase 2 parts

Disassembly

Included with this blog, are a few different exploded views of the pistol, please use them to guide you in removing the parts, which I will list as we go. 

The above parts diagram is for a Phase II gun, which is what I am working on, so the part numbers will match. There are a few differences in this gun from a Phase I gun, but the differences are minor. I will include a Phase 1 parts diagram at the end of the blog for those that have the earlier gun. I believe the Phase 3 guns will have the same parts as the Phase 2 guns.

Start by loosening the rear sight elevation screw 2 turns to relieve tension.

Remove the outer barrel shroud by removing the single screw that is under the barrel in the end of ejector shroud (140-013), then with a slight wiggle, slide the outer shroud off of the barrel. 

There are 5 screws on the left side of the gun, that hold the cover in place. They are all the same length, and it does not matter which hole they go into when the gun is assembled. 

Slowly lift the left side cover, there is only 1 spring that will want to pop out (38A083), and it is the spring that pushes the sliding loading gate into its forward position.  The spring is relatively weak, and not under much tension.  

38T cover off
Here are your thousand words. 

Remove the sliding pellet loader (38A042) and spring (38A083) from its tray. 

Using tweezers, remove the sear spring (38-039) and spring guide (38-089) that is behind the sear (38-040) near the rear of the trigger. 

Next, remove the detent ball (38-064) and spring (600-079) that are in the front of the gun, right below the base pin that the pellet cylinder rotates on. 

Remove the hammer spring (38-B038). It is a long flat spring that goes from the bottom of the grip to the hammer. Use needle-nosed pliers to remove this spring by lifting the bottom straight up out of its resting place. It is not under much tension. 

Depending on which phase your pistol is, there MAY be a small ball detent that is under the rear sight elevation screw, be careful not to lose it if yours has one. You may remove the rear sight and spring now, but it is not necessary for the reseal, or you may cover it with masking tape to hold it in place while working on the gun — your choice. 

You will see a large flat lever assembly (38A054) that goes from the trigger to the front of the gun. On the right side is a small roller (38-125) that is in a raceway, remove this roller. 

Congratulations! You have now removed all of the springy bits that are likely to take flight easily.  

Place your hand over the exposed components, turn the revolver over and remove the valve body screw (150-013) from the false “cylinder” on the right side of the gun.

Turn the gun back over, unscrew the base pin (38-127) on which the cylinder rotates. 

Now remove the pellet cylinder (38-107), the entire valve assembly (38-073), and lever assembly (32A054) all at the same time and set them aside. 

The lever assembly (38A054) is factory assembled with special jigs to assure proper timing and should not be disassembled. 

Remove the trigger (38B034), the trigger spring (38-126), and the transfer bar (38A102). 

Remove the hammer (38-106) and hammer pawl (38-021) that pivots inside the hammer, carefully remove the pawl spring (38-039 and guide (38-081).  

Now for the reason we are here. This airgun leaks and we need to stop that foolishness. 

38T valve breakdown

The diagram shows the valve is broken down in 3 sub-assemblies, 55 (the piercing assembly), 56 (the tube assembly), and 60 (the valve assembly).

TIP: The factory service manual says not to separate the 3 assemblies unless absolutely necessary, but since you will be replacing a seal on each end of the tube, you have to separate them.  It is also better to take them apart so you do not inadvertently bend the tube. 

(I tried it their way first, and DID accidentally bend the tube, and had to correct that problem when putting it back together).

Using 2 small adjustable wrenches, unscrew the copper connector tube and piercing assembly from the valve body, being careful not to bend or break the tube assembly.

A small metal washer (part 51 in the diagram) may come out with the tube assembly, but that is ok, just make sure it goes back in first. 

Then using the same 2 small wrenches, unscrew the piercing assembly from the tube assembly. Do not disassemble the tube assembly itself unless it is absolutely necessary, as it is flared on each end. 

The seal kit

The seal kit Tom ordered for this pistol came with all the parts necessary to reseal the pistol including a small bottle of lubricant I will call Pellgunoil.  It is a very complete kit, and the seals are very good quality compared to others that are sold online. 

38T seal kit
I have labeled the parts to match the part numbers shown in the diagram.

The piercing assembly

38T piercing assembly
The piercing assembly.

Using a wide blade screwdriver, or a spanner wrench, unscrew the guide collar (24), end seal (25), piercing pin (27), and piercing screen (28) from the piercing block. 

Clean the assembly with alcohol and a Q-tip. Using the new parts from the reseal kit, lubricate them with the Pellgunoil, or your choice of lube, and reassemble in reverse order and set aside. 

The tube assembly

38T tube assembly
Tube assembly.

Remove the old small seal (part 65) and lube the new seal and carefully put it over the flared end of the copper tube. 

Remove the old larger seal, (part 17) and lube the new one and carefully put it onto the other end of the tube. Set it aside. 

The valve group

Using a spanner wrench, or needle nosed pliers, or a wide blade screwdriver modified for this purpose, remove valve seat (91), being careful to keep finger or thumb pressure on as it is under spring tension. 

Remove the valve components gently using a dental pick to remove the inner parts.

Pay special attention to the parts orientation as they come out. 

Clean the assembly with alcohol, let it dry, and then lube the parts as you reassemble. 

38T main valve order 1
Main valve order 1.

Lay the cylinder (part 9) large end down on a rag or towel, lube the parts with the Pellgunoil as you assemble them. 

The o-ring (part 88) goes in first, valve washer (part 13) goes in with the small lip down toward the o-ring, and the flat side up toward the valve spring.

The valve spring (78A) is tapered, and the large end goes in first. 

Start stacking the components in order, 22, 78A, 18, 92, install the oring (part 58) on part 91. 

38T main valve order 2
Main valve order 2.

Being careful not to cross-thread the top valve seat (91), tighten until contact is made with the valve washer. Then tighten 1/8 – 1/4 turn more. This will squeeze the o-ring a little to make it seal against the valve body. 

Assembly

Now we are ready to put it all back together.

Hammer and trigger assembly

Wherever there is metal-to-metal contact, lube lightly with moly lube or your choice of lubricant. 

TIP: The key word is LIGHTLY, since the speed the hammer falls does have a direct effect on the velocity, and excess lube could slow the hammer fall. 

Install the hammer pawl (38-021) into the hammer (38-106), and the guide pin (38-081) and spring (38-039), and the small bushing (38-125), and place the hammer on the hammer pivot pin.

Insert the flat hammer spring (38B038) into the lower part of the frame, and into the hammer.

Install the transfer bar (38A102), trigger spring (38-126) and trigger (38B034) onto the trigger pivot pin. The transfer bar goes into the smaller of the 2 holes in the trigger.

The trigger spring goes over the trigger pin, the short leg sits on top of the trigger, the long leg rest on the lower part of the frame as shown in the photo. 

38T trigger and hammer assembly
Trigger and hammer assembled.

The valve group

Carefully screw the tube bushing into the piercing block, taking care not to damage the new seal. But do not tighten it yet.

Insert the metal washer 51 into the valve, and screw the other end of the tube assembly into the valve taking care not to damage that new seal. Again, do not tighten this end yet either. 

38T 38-073
The valve group — assembly 38-073.

As one complete unit, install the cylinder (38-107) (the plastic part that holds the pellets), the valve group (38-073) (the valve, tube and piercing block, and the lever assembly (38A054) (the long silver bar with the spring loaded hook on one end.)

NOTE: the piercing block fits into a matching recess on the right side of the frame, the gas tube should be in the position farthest from the hammer. 

Carefully holding everything in position with the palm of your hand, install the valve body screw (150-013) that holds the valve to the right side of the frame. 

Install the cylinder base pin (38-127).

Check that the gas tube is not rubbing on the hammer, and then tighten both ends of the gas tube. Check the clearance again. 

Install the ball detent (38-064) and spring (600-079) into the front of the cylinder, and the sear (38-040) on its pivot pin below the hammer, then install the sear spring (38-090) and plunger (38-089).

As it sits, the springy things should not want to fly out. 

Double check the bushing on the hammer/lever assembly is in place, the cylinder ball detent and spring are in place, and the sear spring/plunger are in place as indicated by the arrows in the photo below. 

38T springs in place
The springs have been installed (arrows).

Place the pellet loader (part# 38-42) in the loading tray of the main valve body with the rounded or tapered end toward the pellet cylinder. 

We will install the loader spring after the side cover is installed. 

Install the side cover with the 5 screws, they are all the same, so it does not matter where they go. 

Double check the trigger and hammer function in both single action and double action to ensure there is no binding.  

At this stage of assembly, if it is binding, the tube is probably rubbing on the hammer, or you forgot to tighten the valve body screw on the right side of the gun (part# 150-013).

The barrel and shroud

If you took the barrel off, look for the mark the set screw left on the barrel, and install it with that mark aligned with the set screw, insert a 0.004 feeler gauge or shim between the barrel and cylinder, and tighten the set screw (part#38-050).

Install the spring (38A083) for the pellet loader in the grove with the end that is tightly coiled toward the back of the gun, and using tweezers or a similar tool, put the front of the spring under the rear of the loader. 

Install the outer barrel with screw (140-013).

Install the right grip panel with the 2 screws.

Hopefully, you have no leftover parts. 

Now you can function test the gun again, checking that everything moves freely. Install a fresh CO2 cartridge, and check for leaks. 

Here is the Phase 1 parts diagram I promised.

Phase 1 parts

ONE FINAL TIP: The manual suggests using a coin to tighten the piercing screw, because a screwdriver could provide too much leverage and may possibly damage the gun.

If you are into revolvers you should have one of these very neat replicas in your collection. 

Thank you,

Stay safe.

Ian


Quick Shots

by Tom Gaylord
Writing as B.B. Pelletier

Today we have a guest blog by reader Ian McKee who goes by the handle 45Bravo. He tells us about some bits and pieces he is working on.

If you’d like to write a guest post for this blog, please email me at [email protected].

Take it away, 45Bravo.

Quick Shots

by Ian McKee 
Writing as 45Bravo

This report covers:

  • The like-new S&W 79G
  • Refinishing the Crosman MKI/MKII and a test
  • SIG Airgun Stuff — good news
  • SIG Airgun Stuff — bad news
  • Postscript from BB

This report is going to be a little different, instead of a detailed report, it will be just a few short updates on things that I have learned, and what is coming up. 

The like-new S&W 79G

A few months back I reported on a like-new Smith & Wesson 79g I had bought. I have decided that pistol deserves to be in the possession of a collector, not a shooter like me.

A TIP — if you have never noticed, on some of the Smith & Wesson 78G and 79G boxes, it is actually printed as having a box of cartridges and 250 pellets or a sampler pack (like this one) or nothing printed on the box, when it only included the pistol.

SW box 1
This older box shows the full 5 CO2 cartridges and a 250-round tin of pellets.

SW box 2
The newer box for the like-new S&W 79G indicates a sample pack of CO2 cartridges and pellets.

Refinishing the Crosman MKI/MKII and a test

I have 2 Crosman pistols that need refinishing, and a friend sent me 3 more to do for him. 

One of his custom pistols is already stripped to the bare metal, and he likes the look, but it keeps dulling because of no protection from the air. His gun will be finished using clear Duracoat aerosol finish. Brownells sells many types of products and parts for gun enthusiast of all types.

One of my pistols has more metal showing than paint. I intend to strip it and refinish it using Brownells-Aluma Hyde CLEAR finish. The other guns will be refinished with other colors of the same products. I want to test how easy the 2 products are to use, and how well the finishes stand up to use.   

silver Mark II
A friend likes the look of his silver Mark II, but the aluminum keeps dulling from exposure to the atmosphere
.

SIG Airgun Stuff — good news

For those of you that have belt-fed SIG airguns, I am sure you have experienced the issue with having a few good shots, then having one flier spoils the group. Well, there is hope. The belts do come apart very easily. You could rearrange the belt pieces until you have an entire belt that groups well.  It just takes time finding and replacing the chambers that are causing the fliers, and removing them from the equation.

Sig belt pieces
The Sig belts come apart, which means the chambers that cause accuracy problems can be removed.

Sig belt chamber detail
This detail of the black pellet chambers shows the lips that overhang the metal loops, keeping the belt together.

The belt pieces are asymmetrical, so make sure you have them all oriented the same way when re assembling them or you will have feeding problems.

Sig belt link difference
As you can see, the links are asymmetrical and the lips that overhang are only on one side.

Sig belt flipped link
If a link is flipped like this, the belt will not function and feed properly.

SIG Airgun Stuff — bad news

A friend brought me a SIG ASP 226 CO2 pellet pistol he had obtained through his work. It had been used as a display in a retail sporting goods store, and at some point in time, a safety conscious employee had “deactivated” it by drilling out the co2 piercing pin.

Sig ASP 226
Sig ASP 226 sporting CO2 pistol.

The valve design is very simple, and is a cartridge design that is easily removed for replacement or service. 

Sig ASP 226 valve
Here is a look at the valve of the ASP 226 pistol.

I have tried contacting SIG’s airgun division about buying the parts to repair the air gun, through several different channels, eventually talking with one of the reps I had met at the Texas airgun show in 2018.

SIG will let you buy almost any part for their firearms (except the serialized frame) online. The airguns, however, are an entirely different animal.

You have to get an RMA (Return Merchandise Authorization) and send the airgun back to SIG. If it is in warranty, they will assess if it needs to be repaired or replaced. 

If it is out of warranty, or the problem is not related to materials or workmanship, you will be contacted about the cost of repair/replacement, and they will proceed accordingly.

I asked how I could become an Authorized Service Center for SIG airguns, but all airgun service is done in house, or from the manufacturer that built the guns for SIG.

As much as we hate to believe it, a LOT more replica airsoft guns are sold worldwide compared to replica pellet/BB guns.This is partly because of some countries laws restricting airguns that fire metal projectiles, and in other countries, the parent’s perception that a plastic projectile is less dangerous than a metal one. 

Over the years, I have either owned or worked on guns from almost every airsoft manufacturer, I have scoured the many airsoft manufacturers, looking for airsoft companies that produce guns with a similar valve design, but at this point in time, I have come up empty. 

I THINK, Sig has contracted with a company to produce their licensed designs exclusively for them.

While I like SIG firearms and some of their airguns, and own a couple, I am seriously reconsidering any future SIG airgun purchases because of this policy. 

SIG publishes the numbers of “tested to 15,000 rounds”. For some owners that is a lifetime of shooting. For other owners, that number of rounds could be 3 months of shooting with the family in the back yard.

A couple of years ago, SIG introduced the ASP 20 break barrel air rifle, it made a big splash, and was well reviewed by almost everyone. As of now, if your SIG ASP 20 breaks, the gun is no longer in production, and SIG will not repair or replace it since it is out of warranty, and there are no parts available to the public to repair it. You now have a wall hanger

I would like to hear what you readers think about the closed service system for their airgun repair.

Ian

Postscript from BB

This bits-and-pieces guest blog dovetails into tomorrow’s historical blog for the weekend. It’s an airgun we haven’t yet covered.


Let’s make lemonade

by Tom Gaylord
Writing as B.B. Pelletier

History of airguns

This report covers:

  • Lemons
  • The bigger picture
  • Whodunit?
  • So what?
  • They got better
  • The point?
  • Summary

I was all set to begin telling you about my Beeman 400/Diana 75 today. Yes — my rifle is a Beeman 400. I’ve had people tell me Beeman didn’t sell a 400, but I’ve got one to show you. However — not today.

There is one part of the Diana 75 sidelever recoilless air rifle that I had to discuss with you first and, as I thought about it, this one component is more important than the entire target rifle. So today I tell all of you how to make lemonade. Some of you will make it, some will even set up lemonade stands while others will continue to curse the darkness.

Lemons

The world of airguns is replete with lemons. In 2018 I told you the story of a Benjamin 700 that was practically forced upon me at the 2018 Texas Airgun Show by one of our regular readers — I forget who. The price of $95 was certainly good. But then I had to get it fixed and, by the time that was over, I had three times the money invested in the airgun. By the way, that BB repeater now holds air indefinitely and is looking for a new home.

The Schimel was a new CO2 pistol in 1950. It was unique, in that it was a CO2-powered .22 pistol that shot pellets at 550 f.p.s.! However, unlike Crosman who had been building CO2 guns for decades by 1950, the Schimel was made with high-tech all-new materials. Unfortunately many of them did not withstand the test of time. The metal parts welded to one another through electrolysis, the o-ring seals absorbed gas and locked the gun up tight for hours after the cartridge was empty, the paint flaked off all over the gun and the plastic grip scales shrunk and warped over time.

Schimel
The Schimel looks like a P08 German Luger and my wife, Edith, who saw the air pistol first, always called my 9mm 1914 Erfurt Luger a Schimel. 

The bigger picture

Those guns and others like them were unsatisfactory, but they were nothing compared to the tens of thousands of failures that were foisted upon the airgunning public in the 1960s and ’70s. Companies with solid reputations that we still trust today sold tens (hundreds?) of thousands of premium airguns to unsuspecting customers who only found their Achilles heel a decade later. Their piston seals were made of the wrong synthetic material! That material worked well when it was new and fresh but it hardened in the air and slowly turned into a dark yellowish waxy substance that fell apart in small chunks. I have found bits of brownish-yellow wax in the barrels of dozens of these airguns. Not one of them escaped this fate and in 2021 there isn’t one of them that still has its original seals.

124 perished seals
This FWB 124 pistol seal was white-ish when new. This brand new seal has never been in an airgun. Years of exposure to the atmosphere have turned it brown and dried it out. It does the same thing inside an air rifle.

I wrote about one of these airguns in the 15-part series, A shrine built for a Feinwerkbau 124, back in 2010 and 2011. Yes, the legendary Feinwerkbau put the new bound-to-fail synthetic seals on their iconic 124 (and 121, 125 and 127). That’s tens of thousands of airguns, right there! And yes, I did write a 15-part report about the 124. I also wrote a great many more reports about that model over the years. Many of them have been about replacing the original seals with ones made from modern materials. I have probably resealed 12 to 15 model 124s in my time.

Okay, get angry! Why would such a prestigious airgun manufacturer put something that was bound to fail in their finest products. Let’s see. Perhaps they didn’t know?

Why would Coca-Cola change the formula that made them the world’s leading soft drink producer? Why would NASA skip some of the testing for the Hubble Space Telescope before launching it into orbit? I could go on but the answer is always the same — they didn’t know.

Whodunit?

Now we come to the part of today’s report that explains why I didn’t start presenting the Beeman 400/Diana 75 today. You see — Diana also used this new synthetic material in their piston seals. That makes the following models subject to early failure.

Diana 5 pistol
Diana 6 target pistol
Diana 10 target pistol
Diana 60 target rifle
Diana 65 target rifle
Diana 66 target rifle
Diana model 70 rifle
Diana model 72 target rifle
Diana model 75 target rifle

And the companies that sold these airguns under other names, like Beeman, sold them under different model numbers, as well. But wait — there’s more!

Walther also used this synthetic material in their airguns made during this same timeframe. That made the following models that are prone to early failure.

Walther model 55 target rifle
Walther LGV target rifle
Walther LGR target rifle

I have resealed two LGVs for this problem, and I paid someone else to reseal one because he wouldn’t sell me the parts. I have an LGR that was also resealed.

So what?

BB, you’re painting a dismal picture here! This is why I won’t buy a used airgun.

Well, you do what you think is best, but I am telling you that this has opened up a grand world of opportunity to those who can work with it. You can either complain that the lower 40 acres on your Titusville, Pennsylvania, farm is all full of black sticky muck that clogs your plow or you can arrange to sink an oil well and become a millionaire!

Guys, what BB is telling you is there is a huge stock of wonderful airguns rotting away in closets because they suddenly stopped shooting when the barrel filled up with the brown waxy stuff. They would have been thrown away years ago but the supply of round tuits was temporarily exhausted. It’s hard to hold an FWB 124 or a Diana 72 in your hands and not realize what a diamond it is!

They got better

All those prestigious companies who were bamboozled by the early synthetics (remember, Benjamin Braddock — plastic is the future! {from The Graduate}) learned their lesson and made their seals out of new material that lasts virtually forever. They each went a different way but all of them figured it out, just like General Motors figured out that timing belt gears should not be made out of Nylon!

While “they” were figuring it out, the aftermarket guys also got with the program and better synthetic piston seals began showing up worldwide. So today a 124 that’s no longer being used is a loving puppy that needs to be adopted. I once bought one for $35 — from an airgun dealer! I bought a nice one for $200 a few years back — from a gun dealer who took it on a trade in for a “real” gun. That one I still have.

I even bought a 124 complete action in a deluxe stock at a gun show for $50 a few years ago. But I sold that one to another airgunner who said he had a barrel.

The point?

If you haven’t gotten it by now, bless your heart! What I’m saying is that there are thousands of worthy airguns laying around that are simply in need of a new piston seal. These aren’t cheapies, either. These are good airguns. Just look at the list up above again. But their owners don’t appreciate them anymore.

I bet if there was a pristine 1957 Chevy Bel Air parked out in the street and the For Sale sign said its original 283 original engine was’t running, people would find a way to do something about it! BB Pelletier just told you that there are thousands of them and you just have to look for them.

Look in odd places. Don’t look in the car trader magazines for ’57 Chevys. Everybody looks there. Look behind the body shops and repair shops around town. That’s where the mechanic parked them, waiting for the owner to pay his bill. And he never came back. Sure there is no title, but we are talking about airguns — not cars! Don’t need no title for an FWB 124 or an RWS 75.

Read the ‘spensive Gun Broker ads that say “I don’t know how well this RWS Diana 75 rifle works because I don’t have any pellets to shoot in it.” Sure — we all believe that. So you contact that guy and tell him that a piston seal replacement for a Diana 75 will cost you at least $350 — $250 for the work and parts and $100 for shipping both ways. Tell him you’ll give him $250 for his $575 air rifle, plus $50 to ship it and then, if it does have the bad piston seal problem, you do have to pay the rest to get it fixed. And you come out about even. But if it doesn’t… oh, happy day!

Or, you can fix it yourself. Or, you will luck out and discover that it works fine. Or, the seller will discover that he actually does have some .177 pellets and the gun does, in fact, work. Then you ask him what pellets he has and what velocity the rifle shoots them at and he tells you that he doesn’t have a chronograph. And on and on…

Summary

Now I’ve told you all that is behind the piston seals of a Beeman 400/Diana 75. That means that on Monday you can light just one little candle and stop cursing the darkness.


A little about o-rings

by Tom Gaylord
Writing as B.B. Pelletier

o-rings
An assortment of o-rings.

This report covers:

  • History
  • Flexibility is key
  • O-ring failure
  • O-rings as a face seal
  • O-ring-assortments
  • Hardness
  • Some o-ring facts
  • The seats or channels they sit in help o-rings work!
  • O-rings used other ways
  • Summary

An o-ring is a donut-shaped elastomer (pliable) seal that performs sealing functions for hydraulics and gasses. Airguns use o-rings a lot, and for different purposes. They help us enjoy our hobby with a minimum of fuss. But what do we know about them?

History

The first patent for an o-ring was by the Swedish inventor, J.O. Lundberg. It was granted in 1896. Not much is known about him, but Danish machinist, Neils Christensen who came to the U.S. in 1891, patented the o-ring in this country in 1937. No doubt his work originated from his development of a superior air brake that Westinghouse, a leader in air brake technology since George Westinghouse invented the first fail-safe railroad air brake in 1869, gained control of. In World War II the U.S. government declared the o-ring a critical mechanical seal technology and gave it to numerous manufacturers, paying Christensen a stipend of $75,000 for his rights. Long after the war was over and he had passed away his family received another $100,000

Flexibility is key

For an o-ring to work it usually needs to be flexible. One of the most noteworthy failures of an o-ring that was not flexible was the space shuttle Challenger disaster in January, 1986. Caltech physicist and Nobel laureate, Richard Feynman demonstrated that the cold experienced during launch as the rocket rose had hardened the large o-ring that sealed the right solid rocket booster to the point that it crumbled in failure. Let’s see why flexibility is so important.

o-ring
An o-ring sealed two adjoining parts (top and bottom)

o-ring under pressure
When under pressure (gas is coming from the left in this drawing), the o-ring deforms and presses against the tiny opening at the upper right, sealing it tight.

In both drawings I have made the clearances between the parts larger than it should be, to make it easier to see.

O-ring failure

O-rings don’t just fail in aerospace applications. We have seen them fail from rigidity in airguns, too. Read the report titled Crosman Mark I and II reseal to learn a lot more about them. In those two reports we saw how a hardened o-ring crumbles when it’s removed, and how a fresh one reseals the airgun instantly.

Another way an o-ring can fail is if it extrudes (gets squeezed through) the opening it is trying to seal. That happens when the ring material is too soft for the application or the tolerances between parts are too great or the o-ring channel is cut improperly.

O-rings as a face seal

We also see o-rings used as face seals in some airguns. One common use is as the breech seal of a breakbarrel airgun. I have shown you this many times as I rebuilt Diana air rifles over the years. The most recent was the Diana 27S, whose breech seal had hardened from the passage of time. When I replaced it with a fresh o-ring the rifle gained some velocity, though not the 300+ f.p.s. I initially thought.

Diana 27S breech seal
Diana breech seal.

Not all breakbarrel breech seals are o-rings, even though they may look like they are. Weihrauch has used specially designed breech seals that appear to be o-rings when they are installed, but when you examine one outside the airgun you see a big difference.

Weihrauch breech seals
Weihrauch breech seals look like o-rings when they are in the gun, but they are not.

O-ring-assortments

Beware, because here comes The Great Enabler! Several months ago I realized I was buying o-rings one at a time for projects as I needed them. That’s not the wisest thing for a dedicated airgunner to do. So I went online and searched for assortments of o-rings. I found many and it came down to two things — what did I need and how much did I want to spend? For me this is a business expense, so yes it comes out of my pocket — sort of. But when I buy something like this I get to spend it before Uncle Sam can.

When you need an o-ring they are specified by their internal diameter (ID) and the diameter of the ring material. The outside diameter (OD) of the o-ring is just given for informational purposes, because when you think about it, the ID and ring material size determine the OD automatically.

I bought an SAE assortment and a metric assortment, but because they are pliable , they will interchange if they are close. If you want to get really picky, o-rings come in aerospace standard 568 (AS568) and ISO 3601 sizes. They also come in a wide variety of materials with Buna (Nitrile), Neoprene, Urethane, Viton, Teflon (PTFE) and Silicone being some of the most common. Airgunners tend to use Buna, Teflon and Urethane. Buna is more pliable and Urethane is more resistant to tearing and abrasion.

Hardness

A lot of people use the term durometer when referring to o-rings without understanding it. A durometer is a test instrument that measures a nonmetallic material’s resistance to puncture and abrasion. The Shore scale is used. When we talk about o-rings I see the term 90 durometer tossed around a lot. A 90-durometer rating only has real meaning when matched to the Shore hardness scale to which it applies. On the Shore 00 scale a 90 rating is medium hard, while on the Shore D scale a 90 rating is extra hard — almost as hard as it gets! Your car’s tires are a zero to 10 on the Shore D scale and a 90 on the Shore 00 scale.

Some o-ring facts

1. To perform correctly, a hard o-ring needs tighter tolerances than a softer o-ring.
2. An o-ring usually needs lubrication to do its job – but not always.
3. When an o-ring seals something, it only needs to be finger-tight.
4. An o-ring can look fine yet hide a tear or a puncture that will leak under pressure.
5. An o-ring can look ratty yet still seal perfectly.
6. The durometer rating of an o-ring can change over time, as it hardens.

The seats or channels they sit in help o-rings work!

If the seats are too wide or too deep, the o-ring will not seal the joint as intended. Also, the shape of the o-ring seat or channel is somewhat important. While there is a lot of room for slop with an o-ring (that is one of their endearing qualities), you can’t get away with murder. A perfectly square channel with no radius in the corners may present sharp edges to the o-ring under pressure. It can cut the o-ring, causing it to fail quickly!

O-rings used other ways

Besides seals we find other uses for o-rings in airguns. Sometimes they are used to hold things together — sort of like precision rubber bands. I find that a lot in silencers. And a number of rotary magazines use o-rings to hold the pellets inside in place. I’m sure they are used in other ways, as well. We owe a lot to the common o-ring

Summary

There is a lot more to know than what I have presented today. These have just been some of the basics about o-rings. We deal with them so much I thought it would be nice if we knew a few things about them.


My fair Daisy: Repairing a Daisy 717 pistol

by B.B. Pelletier

Blog reader Vince has been disassembling and repairing so many guns lately that I believe no gun will ever leave his house without some part of it being removed, replaced, repaired or refined. He’s a master at fixing just about any gun that crosses his path. Sit back and read as Vince shows you the ins and outs of fixing a Daisy 717 pistol.

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by Vince

A diamond in the rough, that’s what I thought when I looked at the beat-up Daisy 717 in a hole-in-the-wall gun shop not far from my parents’ house just about 2 years ago. Sure, it was a bit ugly, but (as the proprietor demonstrated) it pumped up and went pfffft when you pulled the trigger. So, I let him talk me out of $10 for it.


$10 is a minimal investment for a gun that now sells for $149.

Turns out that going pfffft was about the only thing it did well. Putting pellets on paper in the same spot certainly wasn’t in its repertoire! I fiddled with it on and off for some time. I oiled it and cleaned the barrel, and it got a little better — but not great. It really struggled to do under 1″ at 10 meters for 5 shots, which is about twice the group size I can get from my Marksman 2004 (now known as the Beeman P17).

Barrel, anyone? Fair chance that’s the ticket. For all I know, some ding-dong used to shoot BBs through this thing. Like I probably would have done as a kid. But there’s a complication. I’m aware that Daisy still makes the 717, but they also make the 747 with a superior Lothar Walther barrel — a gun that appears to be identical in every other respect.

I got the parts diagrams and price lists for both pistols, and lo! Barrel aside, everything is indeed the same between the two. Well, except for the metal shells that are stamped 747 instead of 717. But certainly everything else.

Now I had to decide — $18 for the Daisy barrel, or $793 for the Lothar Walther? Ha! Only kidding! The LW barrel is only $50, still a bit steep for me, especially when I’m worse at pistol than I am at rifle. Is it worth the extra bucks? Will Wobbles the Pistol Pointer really be able to tell the difference?

I went to the expert: Mr. B.B. himself, who told me, “Absolutely go for the better barrel. It ain’t MY money!” Well, he didn’t phrase it quite like that, but he certainly did recommend the Lothar Walther. After kicking it around for about 18 months, I finally got off my keister and ordered it. For good measure, I also ordered a new valve assembly for $3. TWO DAYS LATER, I got them. I’m serious — I ordered Thursday, they showed up Saturday.


The replacement parts have arrived.

It wasn’t until I took the above picture that I noticed something. Seems that the new barrel assembly comes WITH all new valve guts, making that extra $3 superfluous. Not even worth sending back. Oh well, live and learn.

Anyway, down to business. The 717 comes apart rather easily, beginning with the three screws you can get to after lifting the pump handle.


Disassembly is a piece of cake.


The cover just lifts off. No little parts go “sproing.”


Before you do anything else, note how the trigger fork engages the valve.

From here, you can either lift the barrel and grip assembly away from the right-hand cover, or you can pull the grip off (rearward and downward) first. It’s not particularly difficult either way.


It didn’t take much to pop this apart.


While you’re at it, you might want to replace the o-ring on the bolt. A standard #006 seems about perfect. (Original old, squished o-ring on left, #006 on right.)


With a little coaxing the barrel slides out the back.

Now, you’re ready to put everything back together. Oil the o-ring on the new barrel assembly and put it all back together in reverse order. When you put the grip back in place, make sure you put the trigger fork over the valve stem as I pointed out in the above photos.

Everything is now all back together, and I’m itching to start punching one-holers. But, there’s a problem. I pumped the gun and heard a very light sssssssss from somewhere. It doesn’t take long to figure out that it’s coming from the muzzle, which means that my brand new valve is leaking. Grrrrrrrr.

Again, I take it apart and pop out the valve.


I took out the valve, again. (I cheated. This is the old barrel. When I originally did this, I neglected to take pictures, so I’m showing these steps using the old barrel as a model.)

Hmmmm. No lint, no dirt, nothing apparently wrong. Aha! Maybe I just need to use that other valve assembly I bought after all! So I grabbed it, reassembled, pumped, and…sssssssssssss.

Right. Back apart, again. Looking at the guts of the valve, it’s obvious that the fault lies either in the valve plunger or the seat. Since I changed the plunger, that leaves the seat. It shows no obvious flaws, but I know that there’s got to be something wrong with it. So, I dug up a rounded Dremel-type stone that will fit the seat.


Dremel-type tool for modifying the seat…ever so slightly.

Gently, by hand, I reface the soft pot metal valve seat. I’m emphasizing gently and pot metal because someone might be tempted to go a little too nuts. The leak was obviously rather small, so the flaw in the seat must be pretty nominal.


Very moderate-to-light pressure while twirling back and forth for a few seconds.

Clean it out, back together again — with the original valve guts — cock it, give ‘er a pump, and…

(Crickets chirping)

No sssssssssssssss! I left it for a few hours and it held just fine. Now I can go back to finding out if my B.B.-induced extravagance on a $10 pistol worked out.

In a word, yes. Suffice to say that my group sizes are cut in half, meaning that it’s shooting at least as good as my Marksman 2004. Which, believe it or not, is saying something, considering how poorly I shoot pistol. One thing that makes it tougher than it has to be is the trigger. It seems awful heavy, and a check with my fishing scale shows it’s breaking at about 6 lbs.

Six pounds? We can do better than that. And I did. I opened ‘er up, again, fiddled with springs and such and cut the trigge-pull weight in half. It’s not quite as straightforward as just putting in a lighter trigger return-spring, because the same spring moves the hammer and opens the valve.

I was able to get around that problem pretty simply. How? That’ll have to wait for another day.