Help needed with regards to 'resetting' a barrel on a QB78

Help needed with regards to 'resetting' a barrel on a QB78

Joined: April 26th, 2005, 10:56 pm

April 2nd, 2010, 4:50 pm #1

My son has a QB78 that was built by Roy @ MountainAir with a .20 cal LW barrel. Gun has always been a tack driver. Last weekend he was trying to install a new muzzle break and without me knowing he was really forcing it onto the barrel without supporting the barrel with his other hand.

So ......

When we went to shoot he was about 2-3 inches off in windage at 20 yards and about 2 inches in elevation. Seemed at little random withmore flyers than we have seen before. His barrel band is slightly loose.

So I am wondering what to do in order to set his barrel 'back' if you will. Should I loosen the allen grub screw on top of the reciever and twist or turn barrel then retighten etc... Also how tight should the barrel band bolt be.

I assume once we rest it we'll just need to resight in his scope.

Any help is appreciated.

~GOD BLESS~

john
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Joined: May 29th, 2004, 2:30 am

April 2nd, 2010, 5:28 pm #2

John, I would loosen the barrel band screw first, then loosen the barrel grub screw. Once loose check to see if the barrel is loose in the receiver. The O-rings should keep it snug. Carefully reset the barrel by turning it slightly. You may be able to eyeball alignment as you reset it. Once in position tighten the grub screw. Last, assuming the barrel band is the original stock plastic version, VERY carefully snug the screw. Use a small screw driver to avoid over tightening it. That screw is thinned in the center to clear the barrel and will snap off VERY easily if over tightened. It just needs to be slightly snug (don't ask me how I know that). Your son probably "tweaked" the barrel when he forced the MB. Hopefully this will make things right again.

Dan
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Joined: November 17th, 2006, 3:51 am

April 2nd, 2010, 7:24 pm #3

To get the muzzle break on he probably "wiggled" it, rotating it left and right while pushing (or even whacking on it) it down. IF anything is going to loosen the grub screw that holds the barrel in place, this will. Will often tweak the barrel band at the same time. take off the scope, loosen both the grub screw and the barrel band, visulally center the barrel to the air tube, tighten everything back up again, and re-zero.


But there is another choice as well. You added weight to the muzzle, and that alone can change the point of impact.
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Joined: June 29th, 2009, 6:38 pm

April 2nd, 2010, 10:00 pm #4

My son has a QB78 that was built by Roy @ MountainAir with a .20 cal LW barrel. Gun has always been a tack driver. Last weekend he was trying to install a new muzzle break and without me knowing he was really forcing it onto the barrel without supporting the barrel with his other hand.

So ......

When we went to shoot he was about 2-3 inches off in windage at 20 yards and about 2 inches in elevation. Seemed at little random withmore flyers than we have seen before. His barrel band is slightly loose.

So I am wondering what to do in order to set his barrel 'back' if you will. Should I loosen the allen grub screw on top of the reciever and twist or turn barrel then retighten etc... Also how tight should the barrel band bolt be.

I assume once we rest it we'll just need to resight in his scope.

Any help is appreciated.

~GOD BLESS~

john
The new brake may be installed off center and you may have pellets clipping the edge of the brake on exit and that will cause exactly what you describe. I would also check that out. If you can, take off the new brake and see how the gun shoots. Then reinstall and check again. Let us know what you find.

Tom



"What, me worry?"
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Joined: November 17th, 2006, 3:51 am

April 2nd, 2010, 11:45 pm #5

#1. Be sure the rifle is EMPTY of co2 and EMPTY of a pellet.
#2. Check #1 again.
#3. Open bolt.
#4. Place a ball of white cotton (or tissue...or wahtever) into the loading area.
#5. Check #1 again.
#6. Arrange a strong light to shine on the white ball.
#7. look down from the muzzle, looking for how well that white circle is centered in the new muzzle device.
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Joined: April 26th, 2005, 10:56 pm

April 8th, 2010, 10:50 pm #6

My son has a QB78 that was built by Roy @ MountainAir with a .20 cal LW barrel. Gun has always been a tack driver. Last weekend he was trying to install a new muzzle break and without me knowing he was really forcing it onto the barrel without supporting the barrel with his other hand.

So ......

When we went to shoot he was about 2-3 inches off in windage at 20 yards and about 2 inches in elevation. Seemed at little random withmore flyers than we have seen before. His barrel band is slightly loose.

So I am wondering what to do in order to set his barrel 'back' if you will. Should I loosen the allen grub screw on top of the reciever and twist or turn barrel then retighten etc... Also how tight should the barrel band bolt be.

I assume once we rest it we'll just need to resight in his scope.

Any help is appreciated.

~GOD BLESS~

john
Thanks to everyone for your help. We fixed the problem and resighted the scope and it was back to shooting like she always had. My son has a MAQB78 in .20 cal and I have a MAQB78 in .22.

here is his in .20 cal




here is my .22




he shot this group @ 25 yards 8 shots with two flyers


Then we happened to see a tree rat. Dropped immediately. Shot was right behind ear


I am still trying to find the right pellet for my 22. Hope to soon so I an get the groups tighter.

~GOD BLESS~

john
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