XS60C PCP Repeater project

[stalwart]

Found, and ordered a 10K gauge, so we can see if the remaining 3 will go at least that far.

In the mean time, I thought that given the 6K gauge has suffered in the accuracy dept (lol), I could go for another blow out. Not looking for numbers... a vivisection.

2 things I'm curious about: How far can I plow the screws through the receiver if I don't go to any pressures past what it takes to do that... Or (more fun), see if we can duplicate the damage done to DT2. Sample of 2?

What do you guys want?

[rsterne]

Interesting results, for sure.... It's only a sample of one, but it gives us more confidence that if the tube and receiver are within the normal tolerances I listed previously, it should be OK.... as you were well under the overlap that would create, right?.... I'm not actually surprised that the threads held, because of the very long engagement.... and we didn't see any sign of the tube pulling out of the receiver in the original failure.... This leads credence to the idea that the tube had a "spiral zipper" failure along the bottom of the threads and the threaded portion ended up like a long spring, unwinding out of the receiver.... Without the tube being found, we may never know....

It appears that the valve screws are the weakest link, and if you replace those, then the stronger ones will plow through the receiver.... both pretty much expected, I think....

Bob

[stalwart]

I agree. It seems clear that your recommendations put the guns well into the safe zone.

After the gauge pegged, I was applying less pressure than it took me to test the rig initially (15K), but not a lot less. My WAG, earlier, is pretty close.

DT3 has .0145" engagement... so we know I can't blow it up after mounting the new 10K gauge (should be here in 3 days), so should I try to dupe the DT2 damage? It's a really nice day out there... . Boom?

[Tommy]

I am glad you are doing this but please be careful
Tom.

[stalwart]

I am glad you are doing this but please be careful
Tom.

No worries, Tom... but, thanks for your concern!

After the first test, I was leery of this whole process. I had expected something like the second test... and the resulting violent mess was a bit of a shock. The force generated was a real eye opener for me (IOW, scared me, although I like the term "startled" better...lol).

Turns out Lloyd's suggestion to restrict the orifice was a great idea, and Butch's suggestion for the juice was a huge help. The process is now quick, not at all as messy as before (cleans up nicely with a rag)... and will be conducted, again, with me around a corner of a steel clad building. I was watching a monitor, and found the whole thing to be rather anticlimactic. When I decided to continue after the gauge pegged, I was expecting a "BOOM", and got a "phttt". Steven G can edit in some 'splosions, if it gets too boring... We may need him.

Now, I want to hurt some guns!

[rokitman60]

Now, I want to hurt some guns!

And your little dog too!!! hee hee hee hee hee hee hee

[stalwart]

Now, I want to hurt some guns!

And your little dog too!!! hee hee hee hee hee hee hee

It's on. Andy (the donor) has given the thumbs up to destroy DT3, for a second sample.

Butch... I'll think of you, as I clean my hands with a rag.

 

[stalwart]

Didn't expect this either...

I ended up stepping on the handle (right at the end, you can see it start to weep). This is what it took to get to 15K, while testing the rig. I was afraid to blow out the hose, or the fitting I was standing over. I let it sit, twice, after that pressure was reached... all it did was weep (not sure from where, but the receiver did swell .006" just behind the tube threads, all the way to my o-ring).

Thank you Andy. It's looking like over pressurization just doesn't explain the "incident".

[stalwart]

The fill cap nut still functions perfectly (measures .824 max  in 1 place... unchanged), and the tube threads screw in smoothly (.855 max... also unchanged).

The receiver F ID, again... up .002", if any.

If I wasn't the guy on the handle, I wouldn't believe it.

[stalwart]

DT4 and 5 are both well within tolerance... so, what to do with them?

[Sfttailrdr46]

I think that with all that has been determined and no missing air tube to examine for failure I think that a brief recap with pictures of the original posted failure pictures and all of your current findings posted under that would go a long way towards reassuring people that the rifles are ok to use when modded correctly. Perhaps some of the experts on these rifles can chime in with their thoughts at this time.

[rsterne]

I assume by "within tolerance" you mean that the "overlap", ie OD of the tube thread minus ID of the receiver, is greater than what you would get by using the maximum receiver ID from the minimum tube OD?.... That would be 0.8580" - 0.8328"= 0.0252".... If the threads exceed that overlap, then at least in theory the threaded joint should have the same strength as the minimum within tolerance threads would.... and you have tested threads less than that without failure....

I am a little gunshy about JUST using the overlap as a measure of safety, however, because we suspect that the mode of failure was not the threads stripping, but the tube cracking at the bottom of the threads because it was tapped too deeply.... It is slightly upsetting that most (all?) of the tubes you have measured are BELOW the 0.858" minimum OD at the threads.... The OD of the DT2, where the threads still held, was only 0.846", a full 0.012" below the minimum tolerance.... If we just go by the minimum OD on the tube threads, it would appear that a large number of the FD-PCP tubes would be disqualified.... while they may well be OK if mated with a receiver that isn't too large on the ID....

The easy answer would be to simply stick with the posted tolerances and tell people that using anything outside that range is totally at their own risk.... Maybe not a bad thing for the GTA to adopt as a policy?.... but it may make a fair number of FD-PCP owners unhappy....

Bob

[rsterne]

I have been reviewing my data on this problem, and I would refer everyone to the scale drawing of the screw threads I made in Reply # 1293 on page 65.... Now that we know that the shear strength of the threads, even at minimum tolerances (or below) is not an issue.... I think we need to concentrate our thoughts on the wall thickness between the bottom of the threads and the ID of the tube.... That area is not only under pressure outboard of the receiver, it may be subject to additional stress from a sideways impact to the tube.... This is similar to the situation on the HiPac that failed at the bottom of the O-ring groove after the valve let go and shot into the guys leg....

Bob

[stalwart]

I assume by "within tolerance" you mean that the "overlap", ie OD of the tube thread minus ID of the receiver, is greater than what you would get by using the maximum receiver ID from the minimum tube OD?.... That would be 0.8580" - 0.8328"= 0.0252".... If the threads exceed that overlap, then at least in theory the threaded joint should have the same strength as the minimum within tolerance threads would.... and you have tested threads less than that without failure....


The easy answer would be to simply stick with the posted tolerances and tell people that using anything outside that range is totally at their own risk.... Maybe not a bad thing for the GTA to adopt as a policy?.... but it may make a fair number of FD-PCP owners unhappy....

Bob

Yeah, I said that wrong!

[rsterne]

The more I think about this, the more I think the GTA should recommend all tubes and receivers be within the standard tolerance ranges for 22mm x 1mm threads.... If the tube threads are smaller, there is a good chance the wall thickness at the bottom of them is reducing the safety margin below acceptable levels, even for the 1500 psi MSWP specified on the FD-PCP website.... IMO....

Bob

[ezman604]

So, is a user friendly safety checklist even advisable? Or do these airguns definitely need to be examined by someone with the proper tools, experience and knowledge? Personally, I would want mine checked out by someone more qualified than myself. Or just park it permanently. Whatever the recommendation is, we need to make certain it is correct the first time before publishing it.
Thanks to all that are helping get this resolved!!!

[stalwart]

Now that we have stepped above my pay grade, I can only say this:

"The easy answer would be to simply stick with the posted tolerances and tell people that using anything outside that range is totally at their own risk.... Maybe not a bad thing for the GTA to adopt as a policy?.... but it may make a fair number of FD-PCP owners unhappy.... ". I don't see GTA as having a choice here. We have proven that the connection is overkill, but without material specs, aren't we asking for trouble if those specs vary? Maybe in the eventual statement, we should specify that 1018 steel, or better, is the basis for these recommendations?

I was thinking about saving the last 2 guns for the boosted tester, and having fun watching the destruction... but, I'm now leaning toward taking them to the "15K" limit my gear is currently capable of, and adding them to the sample list. If we manage to swell the receivers without separation, we would (at least) have a significant indication the threaded connection won't ever be a problem if all the specs are even close to true.

Could we put that to bed with 2 more?

[rsterne]

I would want to see at least 1/8" of exposed threads past the end of the receiver in the next test.... enough to get to where the thread is full depth.... It's hard to tell from the photos, but my FD-PCP looks to have more exposed threads than the ones you have tested so far....

Bob

[stalwart]

I would want to see at least 1/8" of exposed threads past the end of the receiver in the next test.... enough to get to where the thread is full depth.... It's hard to tell from the photos, but my FD-PCP looks to have more exposed threads than the ones you have tested so far....

Bob

Could I stack 2 seals to get that? Or, to retain the full FDPCP threading (instead of adding my own extended threading) go with trimming the receiver in the front?

I'm here, at the shop.. it's a beautiful day... and I'm committed to this thing until not needed any more... say the word.

[rsterne]

Stacking 2 seals might work, if you could get it to seal.... if that won't work, then trimming the front of the receiver.... My tube is no longer in it's original position, it is screwed further into the receiver.... but what I remember is seeing at least 1 full thread that was cut to full depth in front of the receiver....

DEz, one thing that concerns me, is that most (all?) of the tubes Eric has measured are a couple of thou or more under the minimum OD at the threads give in the tolerance tables (mine was right on the minimum).... as in fact is the OD of the XS-60c tubes.... I would hate to come up with a recommend set of measurements that would reject most of the tube out there.... On the other hand, if the threads are below the minimum, then the wall thickness will be reduced as well, and so will the safety margin....

Bob