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Need help with a Burris Scope |
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phatjohn
Optics GrassHopper Joined: February/24/2009 Location: United States Status: Offline Points: 16 |
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Posted: March/03/2009 at 16:37 |
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I purchased a Burris 3x9x40 Fullfield II Tactical with ballistic plex rectical to go on a custom AR-15 flat top build I just completed. I have it mounted in Burris Xtreme Tactical 1" "High" rings. Went to the range today to sight it in.
At 100 yards, my windage adjustment is fine but I have run out of elevation adjustment. My POI is 1 to 1.5 inches low of POA.
At 200 yards. windage is still good but the POI is 3-4 inches below POA. I moved to the second dot on the vertical stadia of the rectical and it helped but I would think I would have enough internal adjustment to sight it my rifle to POA would be equal to POI at 100 to 200 yards.
Any ideas on what could be wrong and how to fix it would be greatly appreciated.
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Molon Labe
You don't get old by being stupid |
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Shenko
Optics Apprentice Joined: April/20/2008 Location: WA Status: Offline Points: 249 |
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Is there any chance that the bell of the scope is touching something?
What base are you using?
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hunter12345
Optics Journeyman Joined: November/21/2007 Status: Offline Points: 470 |
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Sounds like you need to shim the rear mount,try using a soda can or shotgun shell and cut a small piece so it covers only the bottom mount.That should solve your problem.Even expensive scope's like my Leupold VXIII was low by 2 inches at 100 yards, a quick fix by useing a spent shotshell corrected the problem.
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phatjohn
Optics GrassHopper Joined: February/24/2009 Location: United States Status: Offline Points: 16 |
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I've got plenty of room for the bell of the scope, nothing touching the gun front or rear. For the base, I'm using the picatinny rail that is part of the upper receiver (kinda like what Ruger does on their centerfire rifles, base is machined into the top of the reciever).
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Molon Labe
You don't get old by being stupid |
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Urimaginaryfrnd
MODERATOR Resident Redneck Joined: June/20/2005 Location: Iowa Status: Offline Points: 14964 |
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Want to add 22 MOA (thats 22 inches further up at 100 yds) This is the easy way.
Edited by Urimaginaryfrnd - March/03/2009 at 17:20 |
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"Always do the right thing, just because it is the right thing to do". Bobby Paul Doherty Texas Ranger |
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3_tens
Optics Jedi Master Joined: January/08/2007 Location: Oklahoma Status: Offline Points: 7853 |
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Sounds like the barrel may not be seated true in the receiver. |
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Folks ain't got a sense of humor no more. They don't laugh they just get sore.
Need to follow the rules. Just hard to determine which set of rules to follow Now the rules have changed again. |
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phatjohn
Optics GrassHopper Joined: February/24/2009 Location: United States Status: Offline Points: 16 |
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I don't think that if the barrel was seated improperly that I would be getting the tight, consistent groups I'm getting. It's just that my groups are hitting below my point of aim and I can't use the scopes internal adjustment to correct the problem.
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Molon Labe
You don't get old by being stupid |
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ccoker
Optics Master Joined: February/13/2008 Location: Austin, TX Status: Offline Points: 2041 |
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that's strange
never had that issue on an AR
maybe the rings are slightly off spec
do you find enough eye relief ?
most people find they prefer a mount that pushes the scope forward more
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phatjohn
Optics GrassHopper Joined: February/24/2009 Location: United States Status: Offline Points: 16 |
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eye relief is fine. I think I'm going to have to go with a riser as suggested above even though I don't fully understand how it will help. Burris customer service suggested either going with a MOA base or Signature Rings with an insert kit. I just hate having to buy another set of rings or a riser to fix the problem.
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Molon Labe
You don't get old by being stupid |
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rifle looney
Optics Master Joined: November/21/2008 Status: Offline Points: 2553 |
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Phatjohn cant help with your situation. I don't shoot AR's but was wondering how you like that tact scope over all and did compare it with anything ? thanks.
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Dave Wilson
Optics Apprentice Joined: January/29/2009 Status: Offline Points: 88 |
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get the Burris rings with the inserts. they work very well.
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13181 |
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Before you go and start buying new stuff, you should probably figure out what is out of spec.
The first step is to swap out either the scope or the rings and see if the scope is still pointing up. For example, if you put a different scope into the rings and you do not run into the same problem, that would mean that the Burris needs to go back. Conversely, if you plop the Burris into different rings and there is not problem, the rings need to be tossed. Simply adding the riser doe snot necessarily solve the problem if the scope is its source, for example. ILya |
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RONK
Optics Master Extraordinaire Joined: April/05/2007 Location: United States Status: Offline Points: 3199 |
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The rail that Urimaginaryfrnd suggested will correct the problem, as will Signature rings, by in effect, tipping the muzzle (objective) end of the scope downward at an angle in relation to the rifle's bore. You then have to raise the muzzle upward more to get the crosshairs back on target, thus raising your POI about 22 moa, or 22 inches for each 100 yards of distance. Since you are currently only a couple inches low at 100, you'll have to readjust your elevation about 19 inches "Down" to get where you want to be, but then you will probably have plenty of both "Up" and "Down" elevation adjustment remaining in the scope, unless that is defective.
The problem is that you will then have a scope mounted in High rings AND setting on a riser. Too high to get a solid cheekweld on the stock. So you will want to get new Low or Medium rings to get it back down! Or a thick cheek pad or an adjustable comb stock.
Your not done spending money, I'm afraid.
Shims will help, but it's a quick fix and if not done right can result in tube damage or slippage, so don't get too heavy-handed if you go that route.
edited to add: I read Koshkin's post after typing mine; he makes a good point about addressing the cause first.
Edited by RONK - March/04/2009 at 21:20 |
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phatjohn
Optics GrassHopper Joined: February/24/2009 Location: United States Status: Offline Points: 16 |
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koshin and ronk + others who responded to my OP, here is an update to my predicament.
As near as I am able to determine, I think the picatinney rail on top of my rifle is slightly out of spec.
To fix the problem I deferred to two very good friends of mine who own a machine shop and are avid rifle shooters. To keep things short, they fabricated a custom, one off shim set for me the fit is so exact that you literally cannot see it. It cured the problem on the first try!!!!!!!! When I went to the range to re-sight in my rifle, I was shooting over the top of the target stand (about 10-12 inches high at 100 yards). I used the internal adjustment to move the POI to POA and all was well. I now have plenty of vertical adjustment for any situation I may encounter for the intended purpose of this particular rifle. And I am extremely pleased with the way the rifle shoots, MOA @ 100 yds. It's got a NATO chamber and 1:8 twist and seems particularly fond of Nosler Custom Competition 77 gr. FMJBTHP's.
Thank's to all who replied to my post, it really helped me figure out what I needed to do to fix the problem.
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Molon Labe
You don't get old by being stupid |
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phatjohn
Optics GrassHopper Joined: February/24/2009 Location: United States Status: Offline Points: 16 |
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So far, I really like the Tact. FF II scope. I didn't really compare it with anything else because the only scopes that would do a better job for me on this rifle would have been out of my price range. As far as glass quality goes, my eyes are too bad to notice much of a difference between the mid range scopes and the "top of the line" models from the likes of Swaro, Niteforce ect. The XTR rings are monsters, there is so much surface area on them that I can't think of a rifle short of a .50 BMG that they wouldn't be able to handle the recoil from.
I have to admit though, I'm a Burris scope fan. I have several in variable and fixed configurations dating back to the mid to early '80's. I've never personally had a problem with their customer service when I have had to send anything back (which has only been 1 scope in about 20 yrs).
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Molon Labe
You don't get old by being stupid |
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rifle looney
Optics Master Joined: November/21/2008 Status: Offline Points: 2553 |
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Thanks for that reply. I too own an older fullfield from when the turrets were up close to the bell I really like it as well. Glad you got your rig shooting good.
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