More on QB78 Family Main Tube and Tube Cap Lengths

In order to know if your QB78-family air rifle has a short or long Main Tube, you need to measure it. Length of the old, short main tubes is about 14 7/8-inches, length of the new, longer tubes is about 15 3/8-inches. (They're actually made to metric measurements, of course). Long tubes will only work with long tube caps, short ones with short tube caps, due to the fixed length of Powerlets. All other parts are the same.

I spoke to the factory folk about this change when I was in Shanghai, recently. They developed the modification to make it easier to change the tube cap O ring. It applies to all Powerlet-driven QB78 family models, including the AR2078 and AR2078A.

Here's a photo of the old and new Tube Caps.


But some long tubes do not have the gas release hole at the threaded end of the tube - this can cause the tube cap to fly off of the gun if there's residual gas pressure when removing. This is not usually a problem if you know about it, but be aware! I was assured that all future production will include this gas relief hole.

As with most production changes in most factories where the old part is not defective in design, the change from short to long tubes/caps was cut in over time. For example, the most recent cases of guns that arrived with us last month have mostly long tubes, but some - in the same case and number sequence - have short tubes. So, the serial numbers I've posted for the change (08686XXX) should be seen as a guide to about where it began. Measurement is the only sure way to know.

This post amplifies some information posted earlier about the short and long tube caps that match these tube lengths.