Bulk Fill Cap for QB78

[Jonah]

Anybody where to get a bulk fill captor the QB78?

[Ribbonstone]

Short quick answer: don’t know of any place that has one for sale.

Long answer:


Somewhere along the line, the QB78 bulk fill end cap evaporated...they just don't have them to sell.

From something that use to be (way back) included with some rifles….not to be found now.

Noticed some years back they changed the gas tube...it’s a little longer and the tiny emergency vent hole (hidden in the threads) is farther back.  Changed the 12gr end cap to work with the current longer tubes.

Right about that time, the bulk fill end caps disappeared.  Haven’;t been looking hard, but I’ve never seen a factory one for the new longer tubes.

Two on the left are for the older QB78’s….one of the right if for a current Qb78.

DSCN2857 by Robert Dean, on Flickr

 Have had posters swear there is no vent hole in theirs….and it could be hidden under the barrel.  But to get an idea of what that matters.


An old tube...can see the tiny vent.  The red “*” marks about where the current tubes have a tiny vent. To work, the oring on the end cap has to be on the pressure side of the vent, so the old end caps/bulk fill won’t work.



DSCN2853 by Robert Dean, on Flickr



However, if you find one of the old bulk fill end caps….would need to mod it with a lower 0-ring and it will work.  Have to cut a race for the o-ring to seat; lathe work, but just a simple cut and a new o-ring.




Alternative ideas:

Look thorough the custom parts suppliers/rifle makers.   Several DID make one for QB’s…..although discontinued now. 

Can convert a 12gr. end cap. Think that’s what Wil2506 did with one of his...would have to PM him and ask.


If Mike at Flying Dragons had any of the ones he used on the FDPCP’s, it would be pretty much like the old QB78 fill cap (and the short size that needs the new lower o-ring).

[nervoustrigger]

Like Robert, I’m not aware of a source that offers them.  Maybe the XS60C cap has the same threading.  Does anyone know?  If so, maybe try Mike at FDAR.
 
I’ve usually resorted to taking the OEM cap and drilling and tapping it for a Foster fitting.  Kinda tedious but I always keep a spare Foster fitting or two in the parts box, so I end up looking at the two pieces in my hand and realize I can either go looking for a ready-made one and get it in a week (if I can even find one) or break out the tools and have it the same day.  Apparently my impatience exceeds my laziness.

[johnbrown]

In 2018 I have tried to find a bulk fill cap with no luck.

I want a QB78 but on HPA not CO2.
I could buy a QB78s for $60 but I will not because I cannot convert it to HPA.

I have several Crosman 2400KT and 2240 which could be easily converted to HPA using a GMAC Powerlet Eliminator.

No such luck for the QB78.

[nervoustrigger]

I want a QB78 but on HPA not CO2.
I could buy a QB78s for $60 but I will not because I cannot convert it to HPA.

What am I missing?  The synthetic stock precludes converting to HPA? 

I have an example of both converted to HPA by doing nothing other than adding a Foster fitting to the end cap.

[Nvreloader]

Guys
Question....

I have a bulk fill cap, but I am not sure what it fits, Crosman or QB models etc or something else,
has a double "O" rings on the insert of the brass tube shank, and a black plastic plug in the end,
which contains a brass "Star" shaped one-way air passage plug, and there is a standard one-way valve/plug in the fill nozzle?.

The 2 "o" rings are spaced about .350" apart, starting about .150" from the end of the brass tube insert,
and the brass insert is approx .900" long, that the cap fits up to and hold this part into the pressure tube.

I can't seem to get the cap to thread onto a Crossman or QB tube..........the threads inside the cap appear to be fine threading.
(I haven't taken it apart to measure the threading yet etc).

My bulk fill adaptor is very close to Ribbonstone's photo,
except mine has the black plastic plug on the end, (where his is metal) and the 2 "O" rings are spaced along
on the brass part.

Is there a reason I can't take this cap off and bore out a Crosman and or QB cap to fit this bulk fill shank?
How do I tell if this bulk fill adaptor is CO2 or HPA?

Ribbonstone
How far is that hole from the end of the tube?

Thanks,
Don

[nervoustrigger]

I just checked the end cap from my XS60C.  It looks identical to the QB's end cap and threads onto the tube perfectly.  They each look like the right-most example in Robert's picture.  So if you can find a bulk fill cap for the XS60C, I see no reason it won't work on a QB78.

[Bentong]

I just checked the end cap from my XS60C.  It looks identical to the QB's end cap and threads onto the tube perfectly.  They each look like the right-most example in Robert's picture.  So if you can find a bulk fill cap for the XS60C, I see no reason it won't work on a QB78.

Got Gen1 XS60C that I swap around the bulk fill cap with older QB78 with no problem but cannot use the bulk fill cap with my QB78S, vent hole is farther back.

[Ribbonstone]

That's what I found with the XS60C end cap....but it has the length to add a 2nd o ring lower down to make it work with the current QB tubes.

[nervoustrigger]

Got Gen1 XS60C that I swap around the bulk fill cap with older QB78 with no problem but cannot use the bulk fill cap with my QB78S, vent hole is farther back.

Ah okay, thanks for chiming in.  My XS60C is a 1st gen also so I checked my folder on the hard drive and found an early photo, and what do you know?  It's wearing a different end cap.  Then I remembered...the reason its current end cap so strongly resembles one from a QB78 is because it is one from a QB78.  The Mickey Mouse one that came with it was faulty and I had to replace it straight away.

Sorry for the confusion!

So as you say, the XS60C bulk fill cap will work with older QB78 tubes (absent the vent), or newer 78 tubes (with vent) if you add a second O-ring as Robert indicated.

[Ribbonstone]

So close, it’s hard to tell an old QB78 and an XS60 end cap (one from a FDPCP).

DSCN0028 by Robert Dean, on Flickr

But if you had either one, could add a 2nd (lower) o ring race and o ring and it will work with the current QB78 tubes (and still work with the short old QB78 tubes).

DSCN0168 by Robert Dean, on Flickr

Not being able to find either one...rsuspect the question will come up again and again.

[SADave]

This guy was making QB bulk fill caps and selling them on ebay.

Didnt see any currently posted,  he'd had a batch a month or two ago.

https://youtube.com/channel/UChaz79XEuccoBcPL9XNg78Q