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11 February, 2011

QB78 Family Bulk Fill Capabilities

Up-date on 11 May. We now have a solution to this problem. The Archer Airguns Universal Bulk Fill Cap works with any QB78 family air rifle, including those with the 10mm vent hole location that caused the problem outlined in this post.

Over the past couple of weeks, we have received a (fortunately) small number of customer complaints about “leaking Bulk Fill Caps”. Thanks to the help of these customers, I’ve been able to identify the cause of the problem and it seems appropriate to share it here.

The problem is actually NOT due to bulk fill caps leaking.

The cause is, in fact, due to a manufacturing change in positioning of the tiny gas vent hole in the main tube of the gun. This vent hole is the one at the front of the main tube, within the threaded section of the tube, that releases any remaining gas when the tube cap is removed.

The location of this vent hole has varied over the years - some guns have had no vent hole at all - but has typically been about 2.5mm from the end of the tube. However, the most recent guns now have that vent hole about 10mm from the end of the tube. It is this change which has caused the problem.

As you can see from the diagram below, the current long Tube Cap has the O ring slot about 18mm from the outer end of the cap. This means that the O ring in that position will ensure gas tightness in the main tube, irrespective of the vent hole being 2.5mm or 10mm from the end.

But the Industry Brand Bulk Fill End Cap has the groove for its sealing O ring centred only about 7.5mm from the outer end (the same dimension as the old, short, Tube Cap). Due to manufacturing tolerances in O rings and their grooves, these figures are rather approximate.

This means that it works fine with vent holes 2.5mm from the end of the tube, but where the vent hole is 10mm from the end, it MAY not - hence the leaking from some guns when using bulk fill.

This effectively means that guns with the vent hole 10mm from the end of the main tube cannot be guaranteed to be capable of bulk filling using the standard Industry Brand Bulk Fill End Cap.

As far as I can determine, guns with the re-positioned vent holes have serial numbers of about 106XXXXX and above. The guns affected can be AR2078, AR2078A, QB78 Deluxe and QB78 models. Current guns in the US supply chain mostly have serial numbers in the 096XXXXX and 106XXXXX series. I strongly suspect that this issue will also be found on the “OEM branded” versions of the QB78 such as the Tech Force and SMK models.

I am making this issue known so that QB78 family users - and particularly potential purchasers - understand that the latest guns may not be capable of bulk filling.


Anonymous,  Friday, 25 March, 2011  

That sucks.It would have been nice to know the bulk fill problem,before I ordered it!

Stephen Archer Thursday, 31 March, 2011  

I agree it sucks. But Archer Airguns is the only dealer to have identified this problem and then advised our customers in multiple public fora. The factory did not inform us of the issue.

We're also working on a solution that should be available fairly soon. When it is, I'll publish details.

About This Blog

This blog shares information, ideas and knowledge about air rifles. It compliments the information Stephen publishes on the Archer Airguns website, on YouTube and the Chinese Airgun Forum.

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