Canadian Airgun Forum

Ordered in one of these HPA tubes from scopes and ammo. Derek Vinyard did a bang up job on these- great looking tubes...



Shown with the screw driver required for valve installation.



There's the fill fitting, with the heads in shear mounting screws...



...and the fill cap/cover.
I like what I'm seeing so far. It'll be a while before I get it set up on the gun. I'd like to learn the internals of the 78, and shoot the heck out of it on co-2 first. Plus, I'll have to wait a bit to finance a fill source... getting kinda tapped on all this a/g stuff (again)

Regards,

Doc Sharptail

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"Ain't no half-way"
-S.R.V.

After the shoot in Calgary on Saturday and seeing everyone's pcp, I considered buying a pcp tube from S & A. Let me know how it works out for you. Looking forward to seeing more of your review.

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B51
QB78
Crosman Phantom
a pair of 1377s
2240
.357
Sigarms 1911
Condor

What are you guys going to run for a hammer spring to allow 3000 psi fills?.... My experience is that the stock hammer setup on a QB peaks out at about 1200 psi.... I know that some of the older guns had a heavier spring (0.051"), but the new springs all appear to be made from 0.047" wire.... You can shim the spring up to about 1/4", but that still only moves the peak on the velocity up to about 1800 psi with 14.3 gr. pellets and less on heavier ones.... To make full use of a 3000 psi fill, you are going to need a hammer spring that will peak at around 2200-2400 psi.... If you have a source of suitable springs I'd be interested in hearing about it....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!

Life is too short to be wasted worrying about the opinions of others.

Hi Doc..Where Oh Where did you get that Screw Driver? What is the Length?
Got a Ten(10 inch) Blade length from HomeDepot and that was the longest they got; for the standard QB78.
Also sent a Note to Eric(S&A) to ask the same question, how do you tighten up the valve when it is in position.
So, now he might know that is what is needed.
Thank you for the Info...

Why are these tubes refered to as "HPA" and not "PCP"?


Not Doc, but I've got the same driver, from the same location; Princess Auto. OAL is 23.5 to 25 inches(QC is Horrible); just looking at the pic of Doc's, I'd bet his is at least 2 inchs longer than the one I own, as the shaft of mine is ~2" deeper in the handle.

They're often "sale" priced at $3.33; regular price 8 or 9 bucks. HTH's.



G'day Bob! Next time I'm in the the Big Smoke (Winterpeg), I'll take a run down to the local spring shop where in the past I had picked up a small metric crapload of spring stock. If you'd give me a range of OD and wire guage you'd be interested in aquiring, I'll have a look at what they've got in the bins, and send some your way.

All the spring stock from this supplier comes in 12-14" lengths, and is close wound (think expansion spring, not compression). What they advised me to do is stretch the coils to ~110% of desired finished length, and oven cure them (450-500*) for 30 minutes. The 110% is to allow for "set" on the first compression to coil bind. I've got several of these springs running primarily on my DPH'd guns, and they seem to be standing the test of time.

I'm not sure what Doc's plan is, but I'd be guessing it has something to do with a final tune that uses much less than 3K psi for an intial fill. However, similar to yourself, he is a tenacious SOB, and all it'd take for him to figure out how to use a 3K fill, would be for someone like yourself to imply it couldn't be done. . . . .

Really though, lemme know on the wire dims.

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Don't Be Sexist - Broads Hate That.

Blade and shaft section on that screw driver is 24". It came from Princess Auto, and cost me 6.99, yesterday. They had a pile of 50 or so of them at the Panet Rd. store....

As for the hammer springs:

As stated above, it's going to be a while before I get that tube up and running on the gun. I have no intention yet of filling it to 3000 psi- until I know what I'm doing. This is my first hpa tube, and the learning curve looks a little steep right now. Also, as stated above, I want to get the gun down pat on co-2, before I proceed.

I'm not really a fan of shimming hammer springs. From what I've seen, both shimmed and/or heavier hammer springs have a tendency to increase pull weight of the trigger. I'll probably join the multitudes looking for a more powerful hammer spring at a later date.....

Bob- Are you pinning the valve, or valve plug on your 78's on HPA? Inquiring minds wanna know

Regards,

Doc Sharptail

_________________
"Ain't no half-way"
-S.R.V.

Let's clarify something here.

HPA refers to the regulated paintball air/N2 systems that consist of a tank AND regulator set at CO2 pressures for use in markers interchangeably with CO2.

We use these systems in guns like the QB79, Airforce and others.

What you have her Doc is actually a PCP tube for a QB. Your gun will have the capabilities of a Disco once setup.
Let us call it what it is a PCP.

As to the valve with good support from the breech/stock bushing for teh valve I would say 2,000psi is not a problem.
With the valve anchored the same as teh fill then this assembly should be 3,000psi capable. Check with Derick as to his design.

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Walter

http://scopesandammo.com/storefront/pro ... tube-p-361

That's how it's marketed and sold....

If it's a pcp tube, good. If it's what it's being marketed and sold as, good again...

I'd still like to hear back from Bob on his take on pinning these valves, or valve bushing plugs...

Regards,

Doc Sharptail

_________________
"Ain't no half-way"
-S.R.V.

I have made some of these pcp's like the Disco and don't pin the valve 2000 psi and under and 2000 to 3000 psi and pin the valve. As Walter said pin the valve like your fill assembly is pinned on Derek's pcp tube and you will be good for 3000 psi. Walter's advice was right on the money.




George.

The valve needs to be addressed... The tube and fill cap can handle the pressure, but not the valve in it's current state with the current valve stem. It will simply lockup around 1700psi, wouldn't be usable.
Some people pin the valve with fasteners in shear, others part #0200 the inside plug (located directly behind the valve), some do both.

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Daisy Red Ryder
Marksman 2004
Finally acquired a Crosman 760!

Derek, your tubes are looking good there!

What are you using for tube? 4130 o.o65" wall tubing?
I prefer to anchor the valve as that eliminates concern over the fit of the bushing to valve. The other advantage for me is the valve body is easier to chuck in the dividing head for drilling and tapping of the holes.

Oh and the bluing, are you doing your own or farming it out?

Be well
keep up the good work
Walter....

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Walter

Just so"s there's no misunderstanding:

I do want to be safe as possible with this tube. I've had more than one tell me the rear internals need to be secured.

I do have concerns about that small brass section on the QB valve. It's like the old Wendy's commercials-Where's the beef?

At any rate, I won't be proceeding for a while yet...

Regards,

Doc Sharptail

_________________
"Ain't no half-way"
-S.R.V.

I haven't done the math on the valve securing screws, but I will and get back to you.... On the QBs I have worked on, the valve was right up against the steel sleeve, so providing you have all three screws in place before pressurizing it "looked" OK to me, as the screws are significantly bigger than on a Disco.... which also has a total of three screws.... Obviously, if there is a space between the valve and the sleeve, you would either need to shim it, or add screws to the valve....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!

Life is too short to be wasted worrying about the opinions of others.

Here's the math I did on the QB valve attachment.... As usual, we don't know the tensile strength of the screws, so we have to guess.... End force on the valve is 1308 lbs. at 3000 psi.... 872 lbs. at 2000 psi....

Two of the screws are 5mm, the other one (stock bolt) is 6mm (measured at the threads).... Using the minimum diameter at the bottom of the threads to calculate the shear strength.... and using the tensile strength for a Grade 2 fastener (74,000 psi).... derated to 60% for shear loading (44,400 psi).... I get the following....

5mm screws - 827 lbs. at failure each.... times 2 equals 1654 lbs....
6mm screw - 1142 lbs. at failure.... plus 1654 gives a total load at failure of 2796 lbs....

At 3000 psi, that gives a safety margin of 2.14:1.... assuming that the steel is actually 74,000 psi tensile.... If we back down the strength to mild steel (eg. 1010) the tensile would be 53,000 psi, and the shear strength would be 31,800 psi.... That would reduce the total load at failure to 2003 lbs.... and the safety margin at 3000 psi to 1.53:1.... At 2000 psi, the safety margin would be 2.30:1....

I'm personally OK with a safety margin of over 2:1, but that's just me.... If the safety margin is over 2.22:1 then metal fatigue is no longer an issue.... because metal stressed to less than 45% of its tensile strength suffers no degradation from working stress.... The question remains, how good is the steel that the fasteners are made from.... I would think that 2000 psi is not a problem, if you want to be super safe, maybe add some extra screws for 3000 psi....

All of this assumes that the valve is in direct contact with the steel sleeve behind it.... as 2 of the 3 screws are in that sleeve, only 1 is in the valve.... Install the sleeve, push the valve hard back against it, and check to make sure that the valve screw fits accurately into the hole in the tube.... If necessary, add a shim to insure that all 3 screws are taking equal load....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!

Life is too short to be wasted worrying about the opinions of others.

Once again, thank you very much, Bob. This isn't the first time I've gotten an assist from you.

I have a bit of checking to do, and some decisions to make...

Regards,

Doc Sharptail

_________________
"Ain't no half-way"
-S.R.V.