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Drifting problem

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Drumsnguns

Member
Jun 14, 2016
1,007
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North Carolina, United States
So I’ve double checked the scope, lined it up square using a plumb line. Zero’d dead center at 30. I have a bubble level mounted on the scope but at 100 yards it has drifted to the right about 1.5” on a totally calm evening. It generally drifts. 
What am I doing wrong other than being a bad shot. Mind you the group was 10+ shots at just over 1” (personal best). 

Using exact heavy MKll in my Impact. 
 
I quickly checked chairgun and a Jsb 25.4 pellet shot at around 900fps drifts about 3.75" at 100 yards with a 3mph wind (3mph isn't that much at all and might be hard to notice). I know you are using the heavies but my point is it would not take much of a breeze downrange to push your pellets off just a bit at that distance. If they are all grouping well I wouldn't worry about it. :)
 
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If that's your biggest problem,......... personally, I think that's awesome group and shooting!!!
What caliber are you shooting, velocity, weight, type of barrel (smooth twist, straight barrel, choked barrel).
A VERY slight breeze, that you don't think is there, could easily scoot that pellet the 11/2", so I would look there. As I said, it don't take much. 
Another possibility, is, the barrel might have to be indexed, much like benchrest shooters do. I don't know the entire process, but I do know that they will rotate the barrel until the group's end up higher or lower, (I forget which). If the group goes to the left or right, this is an undesirable effect, so they rotate the barrel so the group's are more vertical. This insures that the wind, when it is present, doesn't put the pellet farther than what they can predict.
Some guns' barrels cannot be rotated, due to the transfer port in the barrel, much like a Marauder.
If any seasoned benchrest guys see this post, they may be able to shed some light on this, or clarify some of the points I've made above.
Hope this helps,

Tom Holland 
[email protected] 
Assistant Match Director 
Eastern Suffolk Competitive Airgunners Association (ESCAA)Long Island NY escaaclub.com 
 
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You dont have a problem. 100 yards is far for a diablo pellet. That is great results. Also you may think it is a calm evening but the slightest breeze will make your pellets drift. Try using your first right side mil dot as your bullseye to see if it is you jerking the trigger or just the breeze. I wish I had your problem lol. Good luck.
 
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Congratulation. your shooting with an elite few. When shooting at longer range the slightest breeze will make changes in your POI you wouldn't think possible. Now you have reached this level try going back to the basics and practicing them. Hold on gun, cheek weld, tightness of grip and such. My big nemesis is position of my finger on the trigger. I was astounded how moving your finger around on the trigger would change POI. I have gone so far as to glue a #8 shot BB from a shotgun shell on the trigger so I could feel for the same placement every time. Good luck. sylvan
 
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Thanks guys. Just to say this. I wasn’t really upset at this. Am very happy right now with groups. It did cross my mind that there probably isn’t such a thing as a perfectly windless day and who knows if there is a pocket of wind lurking somewhere out there from muzzle to target at 100. I was just wondering if I was missing something obvious. Rings are accushot with 3 screws per side. . If anyone can recommend better please do. I’ll check video link, thanks. 
I’m shooting a .25 cal Impact with original smooth twist. Using JSB heavy MK II. Pellet speed is around 865 give or take. Hammer is set to max and reg is around 135-140 as best I can tell with OEM FX gauges. 
Again great input. Thank y’all very much. 
Now hoping for weather to improve. Been cooped up too long, cheers!
 
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It's likely one of three things:

1) Scope cant
Shoot at 10 yards to see if the hits lie on the vertical reticle. If they too are hitting slightly to the right, then it is a scope cant issue.

2) Gun cant
Double check your level alignment with the vertical reticle. And make sure that you hold it level when shooting.

3) Wind
If 1 and 2 are OK, then it really is just "drift" caused by a slight down-range cross breeze that you are not seeing/feeling.
 
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"scrane"If the scope is mounted slightly offset laterally from the bore centerline the displacement you describe will occur.
Click to expand...
And if it is, it's easy to correct. Loosen scope in rings. Rotate the scope counterclockwise in the rings. Re-tighten scope rings. Re-zero at 30yd. If done correctly, the poi at 100yd will no longer be to the right of the reticle.
 
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Thought I'd post the target. The group is high, went by Strelok. Actually, I took 16 shots; fifteen were in the main group and the last shot was the low one and checking showed I was off the regulator...honest, ;) Will be checking the scope and testing once the wind dies down. It's honkin' out there!

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I re-checked scope (w/ plumb line) and gun and found that the rifle cant level was off just a hair. Re-aligned it and the gale force winds died down enough today to shoot. I shot groups at 60, 80 and 100 yards.
While on the regulator, groups were well centered but as the gun went off the regulator, the 2nd 80 yard group drifted a little to the left. At 100 yards and back on the reg., once again things went way right even against a very slight/steady right to left wind.
I'm wondering if things might stay better centered if I slowed down to maybe 830-840 fps? Maybe the pellet starts to become unstable at 100 yards at higher speeds (865fps).
I'll try that when conditions approve. All thoughts/ opinions welcome. 
K
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Your still shooting some amazing groups. You might try backing the speed off and see what that does. Also try the MK-I's and MK-II's. Then try just a little lube on them. Somewhere right in there it's going to come together I would think. BUT, then I have days were I wonder. Whats wrong with this gun! Next day it will be fine again. Wasn't gun at all. It's me. sylvan
 
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Sylvan, the last thing you said couldn’t be more true. One day great another day WTH?!? I too figure it’s me. 
What lube do you use? That might be worth looking at again but the left drift at 80 yd, when the gun got off the regulator has me interested in experimenting with speeds. Barrel harmonics might also be coming into play along with diabolo design and stability. Thanks for the input. 
KP

Oh yeah, the Impact prefersthe MKII after trying both. My Cricket likes the MKI a little better. 
 
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KP,
That's the point I was making, that design is much like the Benjamin Marauder. It cannot be rotated, and from what you describe, cannot be rotated as well, because the transfer port has to line up. Some guns do not use a transfer port, thus no extra hole in the barrel for said transfer port. My Steyr had a barrel that could be indexed, as the Air is pushed into the barrel the same place the pellet gets placed in the barrel at the breech. No hole for transfer port.

Tom Holland 
[email protected] 
Assistant Match Director 
Eastern Suffolk Competitive Airgunners Association (ESCAA) Long Island NY escaaclub.com 
 
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