Discovery/Katana POI shifts... Need some advice...

Discovery/Katana POI shifts... Need some advice...

Joined: September 22nd, 2010, 12:29 am

March 29th, 2013, 4:15 pm #1

Hi, All,
I've been trying to dial in my Benji Katana and could use some direction. I'm getting 1/2" and sometimes 3/8" groups at 50 yards,BUT the POI will shift from fill to fill. Yesterday evening I got it dialed for 50 yds, next fill the POI shifted 3/4" down and 3/4" left. Still a very tight group, 1/2" five shots. I am aware of the tiny breech screw issues and have tightened it down. I haven't put a second barrel band in front of the breech yet, but I guess that's my next step. Have tried two different scopes with no difference. I am using cheap Barska rings and may try upgrading to something better like a BKL. I've done some searching on this and i think I've covered just about everything, but any advice from here would be welcome, That tack driver is so close I can taste it! John
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Joined: November 17th, 2006, 3:51 am

March 30th, 2013, 1:11 am #2

If you think a barrel band ahead of the breech might help, then use a plastic tie (one of those ties that zip closed and won't back up) TIGHT at that spot and test. Will look ghetto, but will give you an idea if its worth inletting the stock and fitting the band before you start cutting.
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Joined: September 22nd, 2010, 12:29 am

March 30th, 2013, 4:59 am #3

Cool idea! Will give it a try...Thanks!nt
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Joined: December 28th, 2006, 10:05 pm

April 1st, 2013, 11:41 am #4

Hi, All,
I've been trying to dial in my Benji Katana and could use some direction. I'm getting 1/2" and sometimes 3/8" groups at 50 yards,BUT the POI will shift from fill to fill. Yesterday evening I got it dialed for 50 yds, next fill the POI shifted 3/4" down and 3/4" left. Still a very tight group, 1/2" five shots. I am aware of the tiny breech screw issues and have tightened it down. I haven't put a second barrel band in front of the breech yet, but I guess that's my next step. Have tried two different scopes with no difference. I am using cheap Barska rings and may try upgrading to something better like a BKL. I've done some searching on this and i think I've covered just about everything, but any advice from here would be welcome, That tack driver is so close I can taste it! John
John, have you resolved the issue yet?....nt
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Joined: September 22nd, 2010, 12:29 am

April 1st, 2013, 2:19 pm #5

Haven't had time-I'm hoping to work on it today..got any ideas?nt
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Joined: December 28th, 2006, 10:05 pm

April 1st, 2013, 4:02 pm #6

If that doesn't fix it I have something you can try. I had one that acted very similar to what you describe.

While you have the stock off to install the tie, check to see if there are any hi spots in the stock that are pushing against the air tube. Ideally you want the air tube to be a free float from the gauge port and forward.

I had one that drove me crazy until I figured it out. Metal has a "grain" just like wood and sometimes it will change with pressure. The one I had would actually move into a very slight curve as the air pressure was increased and then relax as the pressure dropped. This wasn't anything that you could notice simply by looking at it. As the tube moved it also moved the barrel and hence the group would also move.

I replaced the air tube and the gun shoots normal now.
I like to use two barrel bands on the Discos.

ART
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Joined: September 22nd, 2010, 12:29 am

April 1st, 2013, 4:10 pm #7

Is your setup one band very close to breech and one out near the muzzle? I've got a band with six screws to use at the muzzle-I adjust so the barrel screws just touch. Haven't even considered the stock might be a factor, I'll inspect for contact marks when I tear down. And to think I thought Chinese springers were frustrating! At least this one shows some amazing poitential, though.
John
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Joined: December 28th, 2006, 10:05 pm

April 1st, 2013, 8:36 pm #8

I position the rear band about 1/2" ahead of the gauge and the front band about 1" behind the fill port dust cover, seems to work good that way. The big thing is getting the breech mounted solid and the band to add additional strength to the whole set up.

ART
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Joined: October 29th, 2008, 2:38 pm

April 4th, 2013, 7:13 pm #9

If that doesn't fix it I have something you can try. I had one that acted very similar to what you describe.

While you have the stock off to install the tie, check to see if there are any hi spots in the stock that are pushing against the air tube. Ideally you want the air tube to be a free float from the gauge port and forward.

I had one that drove me crazy until I figured it out. Metal has a "grain" just like wood and sometimes it will change with pressure. The one I had would actually move into a very slight curve as the air pressure was increased and then relax as the pressure dropped. This wasn't anything that you could notice simply by looking at it. As the tube moved it also moved the barrel and hence the group would also move.

I replaced the air tube and the gun shoots normal now.
I like to use two barrel bands on the Discos.

ART
Art's idea may be the ticket. If not then look to getting the breech mounted good and flat.

I had one that the POI shifted after each fill or from day to day. That was until I figured out how to get that breech correctly mounted flat to the tube. The POI no longer moves from day to day or fill to fill or even as the pressure changes in the tube.

And your correct... these Discovery rifles are very accurate if everything is put together just right.
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Joined: October 29th, 2008, 2:38 pm

April 4th, 2013, 7:19 pm #10

If that doesn't fix it I have something you can try. I had one that acted very similar to what you describe.

While you have the stock off to install the tie, check to see if there are any hi spots in the stock that are pushing against the air tube. Ideally you want the air tube to be a free float from the gauge port and forward.

I had one that drove me crazy until I figured it out. Metal has a "grain" just like wood and sometimes it will change with pressure. The one I had would actually move into a very slight curve as the air pressure was increased and then relax as the pressure dropped. This wasn't anything that you could notice simply by looking at it. As the tube moved it also moved the barrel and hence the group would also move.

I replaced the air tube and the gun shoots normal now.
I like to use two barrel bands on the Discos.

ART
Leave a few inches of wood in place for securing the wood to the gun. You need something for there to tighten up the stock or it will rock on the single mounting screw and that will make things worse.

A piece of 3/4" PVC pipe wrapped with sandpaper works well to remove the wood from the stock. Just be sure to not remove too much.
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