QB78D barrel band moving...

QB78D barrel band moving...

Joined: December 18th, 2009, 3:35 pm

March 23rd, 2012, 12:03 am #1

I was playing with my sons qb78D..

I was having accuracy problem a while ago so I re-crowned it... made a huge difference so been doing some testing when I can at 10m to see how it is doing.

Tonight it was shooting bulls eye every time.... Put it down and picked it back up and 1/2 to the right..... slowing going back to center. I played with things for a bit and realized the barrel band was allowing the barrel to shift. I tightened it as much as I dare but still having slight consistency problems if I touch the barrel.

What does everyone normally do to fix this permanently?

The gun will hit a fly at 20 yards almost every time when its on... but a little bump or site it down leaning against the barrel and it will shoot to the right or left....

Thanks,
Bruce
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Joined: March 3rd, 2005, 1:38 pm

March 23rd, 2012, 1:06 am #2

just need to fix the band to the tube, set screw (non pointed) or can try an adhesive...

mailto:flyingdragonairrifles@hotmail.com Flying Dragon Air Rifles 515-924-3699
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Joined: December 18th, 2009, 3:35 pm

March 23rd, 2012, 1:51 am #3

I was thinking of that but afraid the metal of the band is so thin.. Was also thinking of making a new band from aluminum then the trick would be anodizing...

Thanks,
Bruce
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Joined: September 2nd, 2010, 2:00 am

March 23rd, 2012, 2:03 am #4

I was playing with my sons qb78D..

I was having accuracy problem a while ago so I re-crowned it... made a huge difference so been doing some testing when I can at 10m to see how it is doing.

Tonight it was shooting bulls eye every time.... Put it down and picked it back up and 1/2 to the right..... slowing going back to center. I played with things for a bit and realized the barrel band was allowing the barrel to shift. I tightened it as much as I dare but still having slight consistency problems if I touch the barrel.

What does everyone normally do to fix this permanently?

The gun will hit a fly at 20 yards almost every time when its on... but a little bump or site it down leaning against the barrel and it will shoot to the right or left....

Thanks,
Bruce
I recently observed the same thing on my AR2078.
I put a second grub screw in the breach behind the original, spaced so it's as far back as possible and misses the barrel O-ring. I also replace the original barrel grub screw with a 10-32 stainless one, and I snugged up the barrel band as much as possible. The barrel stays put now.
The original barrel grub screws are a soft steel, M5 thread. The 10-32 screw is almost identical, and being better steel with a well formed socket - you can get it nicely snugged up.
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Joined: November 17th, 2006, 3:51 am

March 23rd, 2012, 2:44 am #5

just need to fix the band to the tube, set screw (non pointed) or can try an adhesive...

mailto:flyingdragonairrifles@hotmail.com Flying Dragon Air Rifles 515-924-3699
Band moves because there is nothing locking it in place...bottom half can rotate on the air tube and pull the top half (and the barrel) along with it. Shim the bottom in place so it won't rotate against common pressures, and it generally stablizes.

Cranking on the cross screw usually just breaks the cross screw.

Can add set screws to the bottom tube (and I'd add them angled in from the top, through the thickest solid part of the band). N

Now the sneaky way to keep the barrel band from rotating is to:

File a flat spot on the bottom of barrel band...be careful here, you do not want to make a flat big/deep enough to weaken the band. Will work with the plastic bands as well as the metal ones. GREASE the band and air tube around the band lightly. Scuff up the inletting in the stock for the barrel band to give it a rough surface and use a dab of epoxy in the inletting for the band. Put the gun together. Once the epoxy is cured, can get it apart because you lightly greased everything the expoxy could contact..and with that flat spot bedded to a spot of epoxy, it an't rotating.

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Joined: December 18th, 2009, 3:35 pm

March 23rd, 2012, 2:57 pm #6

I was playing with my sons qb78D..

I was having accuracy problem a while ago so I re-crowned it... made a huge difference so been doing some testing when I can at 10m to see how it is doing.

Tonight it was shooting bulls eye every time.... Put it down and picked it back up and 1/2 to the right..... slowing going back to center. I played with things for a bit and realized the barrel band was allowing the barrel to shift. I tightened it as much as I dare but still having slight consistency problems if I touch the barrel.

What does everyone normally do to fix this permanently?

The gun will hit a fly at 20 yards almost every time when its on... but a little bump or site it down leaning against the barrel and it will shoot to the right or left....

Thanks,
Bruce
Thanks everyone now I know exactly what to do nt.
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