Canadian Airgun Forum

After my several unsuccessful attempts at making a replacement stem/poppet for my QB Chief I gave up and decided to bite the bullet (pun intended) and order one from Wes as suggested by other members.

Since the QB Chief 2 has a shorter stem, I was careful to order the one specifically made for the original QB Chief but, as I always say, nothing is simple.

When the part arrived (after a week in transit), I was all excited to be able to fix my rifle and I got up all my stuff and tools for the disassembly. Just before starting, I thought that I should probably compare the new part with the original part that was taken out from the Chief to make sure that all the dimensions were good.

I was in for a bit of disappointment, a quick visual comparison confirmed that the new part had a shorter stem than my original part. After measuring them I discovered that the part I received was 2 mm shorter than my part. It was 33mm long instead of the 35mm I needed to be the same length as the original.

I contacted Wes to verify if there could have been a mix up with my order when it was shipped but after he checked his stock, he confirmed that the 33mm was for the Chief and that the Chief 2 had a shorter stem at 31mm. I bought my Beeman QB Chief in November 2017, so I guess that my rifle is probably one of the early first generation which is different than the one Wes used when he took the measurements to have some replacement parts made. He told me to try it and that maybe the shot counts might improve.

This time to avoid another complete takedown if Wes’s part didn’t work, I was extra careful and I checked how all the parts interacted. It didn’t take long to discover that the shorter stem of the Chief’s version I received would not work.

The photo below shows, on the left, the comparison between both stems/poppets and, on the right, that the replacement stem didn’t stick out far enough.



My rifle was scattered all over my bench and the part that I ordered as my last hope for an easy fix didn’t fulfill its promise. The only option I could see to salvage the whole thing would require a little trip to my workshop to machine a tiny extension sleeve.

This could be tricky because the extension couldn’t be permanently attached to the stem for a future disassembly of the valve to be possible. This meant a sliding fit that must be snug enough to stay in place.

Finally, I was able to make a brass extension sleeve that fulfilled all the requirements and I was back in business.

The photo below shows again, on the left, the comparison between both stems/poppets and, on the right, that the replacement stem with the brass extension now sticks out enough.



I mentioned that to Wes and the next time he will order another batch of replacement stems he will ask to have a 35mm version added to the selection.

From that point on, everything was straightforward and after completing the reassembly I was able to fill the rifle without a leak and it was also shooting as it should.

A few days later and a lot of testing, there is still no leak and the rifle is shooting well. I had to do some adjustments because when I reassembled the Chief the preload on the hammer spring was practically non-existent. I had the feeling that it was shooting weaker than before and this seemed to be confirmed by a higher shots count.

The QB Chief is PAL rated and I bought it not too long after the purchase, in mid 2017, of a Benjamin Maximus also PAL rated. Since both pack a lot more punch than my regular stable of under 500fps rifles, they became my platform for experimentation with heavier projectiles.

To understand where it is coming from, I have to say that I acquired a under 500fps 9mm carbine from Bob Sterne (for my 2011 Christmas gift) and a pair of Crosman 1100 Trapmaster (one in 2015 and the other in 2016). The carbine was shooting Eunjin 9mm pellets that were difficult to find and the Trapmasters had their own type of shotgun shells not manufactured anymore.

After I tried making projectiles with all sorts of materials, at the end of 2016, I started experimenting with casting. I bought a lead melter with two molds (a .380 for the Trapmaster and a .350 for the 9mm carbine) to cast lead balls and both worked well when shot from their respective airguns. I wrote a post on the Trapmaster in January 2017 (post501134.html#p501134).

Since I had the necessary equipment, I wanted to cast pellets for my .177 and .22 airguns but, at that time, no mold was available anywhere when searching the internet. The only things popping up were a few swaging systems which was not what I was looking for.

In the Fall of 2017, I decided to try to make a .22 mold from scratch. It is possible to make a mold using basic tools (drills and endmills) for the cavities. It is better with high end equipment as a CNC mill (and since I had access to that kind of machinery, this is how I made my first version) but I made another version using only a band saw, drill press, belt sander and files to prove that it could also be done by artisanal methods.

In both cases, the idea was to stack multiple layers to obtain the shape of the bullet.

The resulting .22 cast bullets are around 34 grains. At that weight, they can only be shot in PAL rated rifles like the Maximus and the QB Chief.

I wanted to revisit the idea using again a CNC mill to make a modular mold where only the central parts would be changed for different shapes or sizes keeping the outer body and the handles common for all variations but never ended up doing it. What happened instead is that a bought, at the end of December 2018, a nice .22 pellet mold manufactured by Noe in the USA. It is casting actual diablolo pellets and those can be shot by any of my other rifles.

This is a long detour, but I am now coming back to the initial topic which was the power adjustment of the QB Chief. When I shot my 34 grains .22 bullets it seems that they didn’t collapse and expand as much as I remembered. Just to make sure I confirmed it by shooting the same projectiles with the Maximus.

After increasing the preload of the hammer spring, I was finally able to improve the power of the Chief but it might not be exactly where it was before the repair because I can now get 40 shots instead of the 30 that I was getting in the past. The bullets deformation being close enough with the one obtained from the Maximus I decided to not fiddle with it anymore.

The picture below shows, on the left, the mold made with the CNC mill with the lead bullets underneath and, on the right, the artisanal mold with the lead bullets underneath.



For reasons that would be self-evident I called the expanded bullets from the group on the left The Muffins and the ones on the right (fired or unfired) The Dumbbells. When I designed the first bullet (the one from the CNC mold), I thought that the large cylinder with the chamfer would be the head and the smaller one, the tail but when I started shooting it, I discovered that I had better result to do it the other way around and ended up with a wadcutter projectile. The smaller disk easily deformed on impact and expanded into the muffin shape. The Dumbbell was intended to be shot with the domed portion forward and it worked well like that.

In conclusion, I am happy to have my QB Chief operational and hopefully the new valve stem/poppet will be good for years of enjoyment.

Cheers.

R-Gun Pete

Even if I am happy that the rifle is repaired, I am still a bit annoyed, frustrated, and unsatisfied about what went wrong with my own versions of the replacement stem/poppet.

I received some general answers but what I experienced doesn’t make sense until I can understand where it has failed in my particular scenarios.

My first and second version were nearly identical except for the material of the sealing disks.

With the first version, the leak was still there but it was a slow leak and the rifle was shooting. I assumed the plastic was too hard and went to a softer rubbery material for the disk in the second version. The second version eliminated the leak completely but the drawback was that the airgun was not shooting either and I had to partially unscrew the pressure gauge to release the air it because the degassing tool didn’t work. From what I was told the rubbery gasket is compressed by the air pressure and the hammer force has to uncompress it before it could open and this makes sense to me.

This picture shows my first and second version and also a design similar to what I did that I found on the internet when I did some research after my failure. So it seems that somebody was having in the same line of thought as me where the valve stem/poppet can be reused and only the sealing material changed.



For the third version, I went to a face seal in the form of an o-ring deeply embedded in the head. As there are only a few thousands of an inch sticking out I thought that the decompression should be minimal and furthermore, unless I am completely mistaken, the footprint of the contact has been reduced a lot compared to the full surface contact of versions 1 and 2.

This is another case where it was sealing very well. In this case I could shoot the rifle only if I didn’t exceed 300 psi. After that point, no leaking but no shooting either. The degassing tool worked until it didn’t and, again, I had to unscrew the pressure gauge to release the air. This one didn’t make sense to me because I was told that the o-ring would get displaced but when I disassembled the valve it was still sitting deeply in its groove and looked the same as when I installed it. I also don’t understand why the valve didn’t opened at all. Getting weaker shots because some of the hammer blow was lost to crack open the valve would make sense to me but not a complete lock up.

This is the picture of that third version and how I expected it to work.



Since the best result I had at this point was with the first version, I decided to revisit it. After examination I decided to polish the sealing face to remove the machining marks.

After reassembly, I started to pressurize it and every 200 psi I was testing that it was sealing and was also shooting. I was able to bring it to full 2000 psi pressure without a leak and the rifle was shooting.

It went in storage for several hours and it was still pressurized when I got it out.

It is when I shot it that all hell broke loose. It was leaking full blast and multiple dry fired shots didn’t stop it until the pressure was really low.

I went through the cycles several times and discovered that it was holding air until the pressure reached 1000 psi then it would start leaking by itself.

Again it doesn’t make sense to me. Why is it holding air and starts leaking when the pressure is higher? I would expect that the higher the pressure the tighter the seal would be. Unless the air finds another path as shown in my picture below.



Anyway I already gave up and bought the part that fixed my problem so it is not really an issue anymore, nevertheless it would be more satisfying to understand why my solutions failed.

If somebody has some explanations related to my specific approaches, I would like to know them in order to understand better what was going on.

Thanks.

R-Gun Pete

Well, I'm glad you got it fixed; I have no explanation for your failed home made poppets other than the the seal materials are deforming unpredictably. Anyhow, you have data to show Delrin works.
I believe you have a Chrony, so why don't you run some chrony numbers on the Chief and the Maximus with your dumb bells (dumpells?) fps and FPE would be interesting. BTW I really like your dumpell design, although I know for sure it takes a lot of work and skill not only to manufacture the molds but also to carry out the casting and swaging.

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Age quod Agis, et semper ubi sub ubi.

Hi Duke.

You are right. Delrin works. I will probably have to order some on Amazon but I am not sure if they have the actual Delrin or just the generic acetal. I will have to investigate.

As for chronying my lead bullets, I am a bit lazy but I guess I should set it up and run some tests with both rifles as you suggested. It might be interesting.

Have a nice evening.

Pete

i was able to use a crosman 2240 CO2 seal for sealing the poppet
https://www.ebay.com/itm/301387705493

Generic acetal is what delrin is. Just that 3m or whoever it is put the name 'delrin' on it.
Don't buy from Amazon. Too much money, check out aircraftspruce.ca they have everything you need, or if possible shop local. Delrin is cheap if they'll cut you a piece.

And get white, or natural. Black apparently has a dye to make it black, and can have some inclusions in it, making it a poor choice for poppet seals. I believe it is a bit weaker as well. Also it smells funny when you machine it

Hi Pistolero!

I used your link but it shows a resealing kit for the 2240. I am not sure which seal you suggested but at this price it is probably best to buy the stem/poppet intended for the QB chief.

Thanks.

R-Gun Pete

Hi Killercrow.

I went to the site you suggested and you are absolutely right, the price are more reasonable than on Amazon.

I checked quickly through their site but I cannot find how much it might be for shipping.

If you ordered from them you might be able to give me an idea. It seems that they are located in Ontario which is also where I am living, so it is not too far.

Is it better to order in shorter length (like several one foot pieces) or it doesn't really matter?

Also what are the best diameters to order?

Thanks.

R-Gun Pete

yes that's the one i use, the orange reseal for the CO2, i pryed the delrin and squeeze that orange reseal rubber into the hole, but i use it for the 2240 hipac and it works

They charge fairly for shipping... Best way to find out would be to fill your cart with lengths of materials in mind and go to checkout, it gives you a shipping quote if you supply your details.

As for diameter? Depends what you want to build. Poppets alone, I'd go with 3/8". Whatever you feel you can make work. Obviously you can make smaller, not bigger.

You know, just a little pondering here ...
Not to say alter your gun to fit the stem length that you have now, which is shorter than OEM... But now, as long as the hammer has a clear path and won't clip any screws or contact the valve body... I guess you need to account for the cocking pins too.
But say it all works out, you gained an extra 2mm of hammer stroke. That does count for something.

Maybe if it were feasible, drill and tap the hammer, install an adjustable striker... Pretty simple ish looking task if you have some tools.

Hi Pistolero.

I understand now, the link you provided was just to show the part, if you have it in your possession it would make sense to use it.

Thanks.

R-Gun Pete

Hi Killercrow.

Thanks for the hammer suggestion.

It seems that my first two entries of this topic might not have been clear enough.

The first was covering the successful repair of the QB Chief. It is now fully functional and nothing else needs to be done. The shorter stem was handled by making an extension sleeve and it solved the problem without any modification to the original rifle.

The second entry was to find some clues about why my versions of the stem/poppet ended up as failures. I cannot make sense of what was wrong and I was interested to learn from my mistakes by having some input specific to what I tried.

Anyway at this point I should probably let go and just forget about it.

Thanks for the info about the Delrin.

R-Gun Pete

I remember many years ago when I brought home from Canadian Tire the Crosman 2289 backpacker. I immediately tried to shoot squirrel in my backyard. That beast would thumb its nose at me because this airgun was grossly under-powered. I gave it 5 or 6 pumps, the speed was at borderline of 300 fps. I disassembled it and found that the valve was made of "white plastics". I could not help but to scold Crosman for making this airgun cheap by using plastic valve and plastic breech. Since the only purpose at that time was to plug the hole, I just assembled it back and replaced the breech with a steel one so I could mount a scope. I did come up with two valve designs. The first one was like yours: aluminum with o-ring. The core diameter should be larger than ID of o-ring so the o-ring is under tension. The groove edges should be slightly lipped. When the hammer strikes the stem, high pressure air would not go the back side to lift up the o-ring. The second design was to use a solenoid to open the valve. The trigger became a switch with negligible resistance force. When the trigger switch is closed, the circuit board would send a capacitive discharge current to the solenoid to open the valve. I didn't do any mod to the valve. Anyways, the backpacker was used at my cottage in Kenora. It worked pretty good for target practice at 15 to 20 yards distance.

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Crosman 2289