XS60C PCP Repeater project

[QVTom]

Stalwart,
Are you willing to make new nuts to achieve your 3k0 fill goal?  If so the logical path would be to make two changes.  1) use a material like 1144 for its strength and ease of machining. 2) Increase the OD to give more wall thickness in the threaded area.  Is the room in between the nut and barrel to add diameter?  If so, how much? 

Tom

[rsterne]

Tom, the existing nut touches the barrel now, unless you put a spacer under the barrel in the barrel band to shim it slightly, then it just misses.... The OD of the existing nut is knurled with lengthwise grooves.... One thing, though, isn't the OD of a 22mm thread 0.866" instead of 0.878".... or is the larger number you used the Max. D of the female thread?....

Bob

[stalwart]

Stalwart,
Are you willing to make new nuts to achieve your 3k0 fill goal?  If so the logical path would be to make two changes.  1) use a material like 1144 for its strength and ease of machining. 2) Increase the OD to give more wall thickness in the threaded area.  Is the room in between the nut and barrel to add diameter?  If so, how much? 

Tom

Tom, I had hoped to both give the guys who already own my caps the option of upgrading their rifles in the future to 3 or 4.5K, without needing a different set up... and also to allow me to stock less part#s. Given the machine time needed to make a nut, and a cap... I don't see that making sense. The guys buying the 3Ks would be paying more than necessary.

Looks like I'm going to go with an internal thread in the tube. I sure appreciate the effort you made (guys, he did a second sim with thicker ridge... got the same results).

It looks like I will be eventually offering screw in 1.5K tubes with the internal set up, so a 3-4.5K upgrade would not need a new cap. I'll keep the standard style available for guys who have FDPCPs, and are happy at lower pressures. I think I can make the internal style look pretty clean.

[QVTom]

Tom, the existing nut touches the barrel now, unless you put a spacer under the barrel in the barrel band to shim it slightly, then it just misses.... The OD of the existing nut is knurled with lengthwise grooves.... One thing, though, isn't the OD of a 22mm thread 0.866" instead of 0.878".... or is the larger number you used the Max. D of the female thread?....

Bob

Yes the larger number was used (max for m22x1).  With the large variation in tolerances of the few examples best error on safety.  An enterprising air gunner could do a hydro test on the FD setup to see where it actually at. My guess you wouldn't need more that 4k0 test pressure to pop it unless that nut is some special material which I doubt.

FD-PCP tinkerers PLEASE be careful and DON'T EXCEED CO2 on a hot day (1k5 psi) pressures with a stock setup.

Tom

[QVTom]

Stalwart,
Are you willing to make new nuts to achieve your 3k0 fill goal?  If so the logical path would be to make two changes.  1) use a material like 1144 for its strength and ease of machining. 2) Increase the OD to give more wall thickness in the threaded area.  Is the room in between the nut and barrel to add diameter?  If so, how much? 

Tom

Tom, I had hoped to both give the guys who already own my caps the option of upgrading their rifles in the future to 3 or 4.5K, without needing a different set up... and also to allow me to stock less part#s. Given the machine time needed to make a nut, and a cap... I don't see that making sense. The guys buying the 3Ks would be paying more than necessary.

Looks like I'm going to go with an internal thread in the tube. I sure appreciate the effort you made (guys, he did a second sim with thicker ridge... got the same results).

It looks like I will be eventually offering screw in 1.5K tubes with the internal set up, so a 3-4.5K upgrade would not need a new cap. I'll keep the standard style available for guys who have FDPCPs, and are happy at lower pressures. I think I can make the internal style look pretty clean.

I like the idea of internal threads, my favorite method by far.

Tom

[rsterne]

I agree, and in CrMoly a huge safety margin....

Bob

[stalwart]

Tom, the existing nut touches the barrel now, unless you put a spacer under the barrel in the barrel band to shim it slightly, then it just misses.... The OD of the existing nut is knurled with lengthwise grooves.... One thing, though, isn't the OD of a 22mm thread 0.866" instead of 0.878".... or is the larger number you used the Max. D of the female thread?....

Bob

Yes the larger number was used (max for m22x1).  With the large variation in tolerances of the few examples best error on safety.  An enterprising air gunner could do a hydro test on the FD setup to see where it actually at. My guess you wouldn't need more that 4k0 test pressure to pop it unless that nut is some special material which I doubt.

FD-PCP tinkerers PLEASE be careful and DON'T EXCEED CO2 on a hot day (1k5 psi) pressures with a stock setup.

Tom

Amen.

[Yarp]

Regarding the safety issue stated above.

Would someone take the time to explain the term, 1K5? Until seeing this repeated I assumed this to be a typo for 1.5K which seemed to be a good estimate of the pressure in a carbon dioxide cylinder stored in a car trunk in my part of the world.

Also, as per the graph below, the temperature pressure relationship varies significantly with the percent of a CO2 cylinder's "rated" fill. The curve between 80% and 100% for temperatures of 90 degrees and 120 degrees F is astounding. There seems to be a good deal more uncertainty here than I anticipated and I'm wondering if some of us might "chip in" for a pressure test. I'm definitely game.

Thank You.

[QVTom]

David, 1k5 is shorthand for 1500.  The k being 1000. 

I believe the max accepted working pressure for CO2  1800 (1k8)psi.  I'm sure Bob can add more information.

Tom 

[StevenG]

David, 1k5 is shorthand for 1500.  The k being 1000. 

I believe the max accepted working pressure for CO2  1800 (1k8)psi.  I'm sure Bob can add more information.

Tom

1k5 would be 1005. If I understand this correctly. 1.5k would be 1500.
Or is this some odd notation style I have never seen before?

[rsterne]

1K5 means 1.5K or 1500 psi.... 1005 psi would be 1K005, the K replaces the decimal point in that type of notation.... The maximum safe working pressure for CO2 is that found stamped on CO2 tanks, 1800 psi.... A properly filled (to 100% of rated capacity by weight) CO2 tank is about 1900 psi at 120*K, which is the maximum temperature marked right on most CO2 cartridges....

My concerns with many of the Chinese made CO2 guns, including the QB79, are that I think (no proof) that they used 850 psi for their MSWP in their calculations, or they didn't do any.... The screws holding the tank block on a QB79 are WAYYYYYY  too close to the end of the tube, and if you take the stock off and put it in a car on a hot day, filled with CO2, and then examine those screw holes afterwards, you will find that the end of the tube is no longer flat, that the tube has distorted from the force of the screws.... This doesn't seem to happen if the two stock screws are in place, from what I have seen and heard, but to me it indicates just how close they are running to disaster.... I know of one QB79 that was converted to HPA that had a regulator leak and the tank and tank block assembly blew off the end of the gun during filling at 2600 psi.... The screws sheared, and the holes in the tube partially tore as well.... The tank assembly went spinning across the shop floor, the gun went flying the other way, but fortunately, nobody was hurt.... There were two problems there that contributed to the failure, besides the design.... One, the stock was not inletted for the tank block, so the block was not supported by those two extra screws (a very common thing for modded QB78s) and Two, the regulator only had one burst disc, a 3K to protect the tank, and nothing to protect the downstream side from going over 1800 psi (good paintball regulators have a 1.8K burst disc fitted, this cheaper design didn't).... The same thing could have happened if the 1.8K disc was replaced by a 3K, which is common practice when guys mod the HPA regulator over 1500 psi.... With a 3:1 or greater safety margin recommended for (every part of) the  strength of HPA systems, that failure at 2600 psi means the MSWP of the QB79 action, when removed from the stock, is 867 psi....

I questioned a few of the things about the FD-PCP and got my fingers wrapped, so I will not comment further.... It is interesting to see this data, however, as the safety of the fill fitting retaining nut is something I never even looked at....

Bob

[Yarp]

Many thanks for the education.
It would be interesting to test a few of these cylinders to failure. Would it be better to discuss this possibility on another thread?

Addendum:
It should be understood that this is not intended to express concern for the integrity of cylinders in unmodified PCPs. 

[stalwart]

I would prefer having that discussion right here, David. In fact... Please?

Quite a while ago, I offered to chip in a gun for testing, as airgunwarriors said he had access to facilities. It never gelled. If you want to set it up, I'd be thrilled to see the numbers... either way.

I have considered trying something here, using a Porta-Power type set up. I trust Bob's math implicitly, and would love to see just how high we'd have to go to blow a 3K up.

[rsterne]

Lloyd has done quite a bit of destructive testing, using air over oil hydraulics (no air in the test part, only to pressurize the oil).... However, I really like the idea of using a Porta-Power, making SURE the entire system is air-free, using a good pressure gauge (ideally with tell-tale), and working behind a suitable safety shield.... The thing to remember is that whatever the pressure at failure, the MSWP should be a third of that or less.... The only exception to that, for me, (and I'm not recommending this, it's just my opinion) is things like settling in of screw heads into the pockets in a tube to equalize the loads, which I actually view as desireable, and will accept on my personal guns at about a 2:1 margin (using yield strength) above what I use for an MSWP....

I can tell you that Crosman 22XX tubes have been tested to 10,000 psi without failure, but we don't know the grade of the tubing, even though they are also 7/8" OD x 0.065" wall.... tested at full wall thickness, of course....

Bob

[StevenG]

1K5 means 1.5K or 1500 psi.... 1005 psi would be 1K005, the K replaces the decimal point in that type of notation....

Interesting. Where does this style of notation come from?
I am used to placing the units at the end. Like 4.5GiB, 4.6Kg, or 5l. That is SI style notation. Commonly used in Scientific and IT realms.

I assume 1k5 means 1451psi-1549psi? Or is there another way to determine significant digits? Or does this notation assume a margin of error instead?

I love minutiae like this.
 

[rsterne]

I don't think it's designed to be used to indicate significant digits, but yes, I would round the results as per your example.... I have no idea where it comes from, but seems quite common in engineering circles.... The units, if specified, would still be placed at the end.... as in 1K5 (psi)....

Bob

[Yarp]

I would prefer having that discussion right here, David. In fact... Please?

Quite a while ago, I offered to chip in a gun for testing, as airgunwarriors said he had access to facilities. It never gelled. If you want to set it up, I'd be thrilled to see the numbers... either way.

I have considered trying something here, using a Porta-Power type set up. I trust Bob's math implicitly, and would love to see just how high we'd have to go to blow a 3K up.

I'll poll my two relevant contacts. The best bet is a former employer up north. The other is a testing lab a few miles down the road. What's your estimate of the minimum meaningful test pressure?

[rsterne]

Since we are interested in 3000 psi fills on stalwart's 3K gun, the gun should be tested to at least 10,000 psi.... If it stands that and nothing happens, no changes are needed for a 3K fill.... The way the FD-PCP was originally sold, as a 1500 psi gun, the test equipment should be capable of at least 5,000 psi, with 4500 psi being required for a 3:1 safety factor.... Since the vendor has said more than once in his gate not to fill the gun above 2,000 psi without undertaking precautions (ie safety mods), that implies a 6,600 psi minimum test pressure, with anything over 6,000 psi supporting a 2K MSWP....

I personally think that if would be great if both stock and 3K versions are tested to failure.... If the failure occurs at a lower pressure than 3:1, but in a non-catastrophic manner (eg. an O-ring leaking, or the screws deforming the supporting structure (but not tearing or rupturing it), then that may or may not be OK.... However, if the failure is sudden and catastrophic, then the 3:1 rule over MSWP pressure should be applied, IMO.... ie record the failure pressure, and take one third of that as the safe maximum.... No failure should be allowed below a safety factor of 2:1, again IMO....

When you consider that 4500 psi filling equipment is now relatively easy to obtain, it could be argued that any gun or tank filled with HPA should be safe for repeated fills to that pressure without danger of sudden and catastrophic failure, and I know I am not alone in that opinion.... If you fill from such equipment, there is always the possibility of that happening, even when using a regulator (they can fail).... I would note that these comments apply to all brands of PCPs, and to "self-builds" as well.... This does NOT mean that 4500 psi is the MSWP, but an acceptable test level unless you ONLY fill from equipment not capable of that pressure (eg. a hand pump)....

Bob

[RHytonen]

Regarding the safety issue stated above.

Would someone take the time to explain the term, 1K5? Thank You.

(having been explained above) I would just like to add, I've seen it in many non-airgun places, most  quite technical and some professional. (retired BSEE here;)
I believe it is, at the least, one de facto standard (of many.)
HTH,
Rod

[rsterne]

After months of thinking and waiting for winter to get here and ordering parts, I finally got my box of goodies to build the Grizzly prototype yesterday.... In case you don't know, the Grizzly is a .30 cal repeater with a 22CI 3000 psi tank, regulated to 2000 psi, with the receiver bored out for a through tube to eliminate the threads in the receiver.... The rest of the details will fall into place as Eric and I proceed with this build.... The purpose of these posts will be to let you see what goes into this gun, and follow the progress....

I got right into modding the Grizzly today, the first thing I tackled was the valve to see how big I could make it.... The good news is that I first drilled the throat to 17/64” (0.266”) and then I managed to use a 7/32” (0.219”) mill on a 20* angle to bore out the exhaust port.... I then used a 1/2” mill to bore out the rear of the valve, and completely removed the raised portion of the seat and drilled the hole for the stem to 1/8” and dropped in an MRod poppet.... Between the smaller poppet OD and the larger valve ID, there is lots of room for airflow.... I drilled the front of the valve to 3/8” instead of milling the slots bigger, and will use a tapered spring.... More on that when they come in....
 

 
The stem of the MRod poppet is a lot shorter, as below, but we have a solution for that.... Note the HUGE port, 75% of the bore diameter for the .30 cal....
 

 
The striker on the hammer can be extended, into the hole in the steel backing block, so that is not an issue.... What IS a problem is going to be getting a signficant increase in the travel.... As I see it, the lug that catches the sear will hit the front trigger mounting lug leaving only 0.8” maximum travel, including the valve lift.... This photo shows the cocked position....
 

 
and this photo shows the sear lug on the hammer where it would run into the front mounting lug for the trigger, which is inside the tube....
 

 
All the rest of the stuff on the hammer is not a big deal, from what I can see.... The striker portion can be longer and thinner to fit through the backing block.... The entire hammer should be able to be 0.74” diameter, except for a flat machined on the bottom in front of and behind the lug that catches the sear.... Therefore, we can certainly make the hammer a lot heavier.... Eric has an idea on how to avoid the interference with the trigger mounting lug to get more travel, which would be nice.... More info to follow as it develops....
 
Bob