Spin drift or other issue?

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guydudeman

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Minuteman
Apr 19, 2024
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Canada
#1
Hi

I am fairly new to precision rimfire.

Tikka T1x. Arken sh4. Sk match ammo.
50 yard zero. Area 419 20moa rail. Arken rings

I am grouping well at both 50 and 100 yards. My point of impact is dead on at 50 and punching one hole. At 100 yards I am my point of impact is .1 mil right of point of aim. Is this a normal amount of spin drift?

The range I shoot at has large berms along the side and gets almost no cross wind. Testing has been on multiple days at very calm weather no perceived wind.

I am just wondering if this would be a normal amount or if I should be looking at my scope mount or other setup issues.

I use this for prs rimfire matches
 
#2
Just trying to rule out wind for sure... does the wind travel the same direction as your bullet, even though there are berms there? 100y is still a decent ways for a 22lr to travel and not be affected by the wind, however small it is. And just because there are berms doesn't mean there isn't still air movement below them.
 
#5
guydudeman said:
Hi

I am fairly new to precision rimfire.

Tikka T1x. Arken sh4. Sk match ammo.
50 yard zero. Area 419 20moa rail. Arken rings

I am grouping well at both 50 and 100 yards. My point of impact is dead on at 50 and punching one hole. At 100 yards I am my point of impact is .1 mil right of point of aim. Is this a normal amount of spin drift?

The range I shoot at has large berms along the side and gets almost no cross wind. Testing has been on multiple days at very calm weather no perceived wind.

I am just wondering if this would be a normal amount or if I should be looking at my scope mount or other setup issues.

I use this for prs rimfire matches
Click to expand...
At 100 yards it hasn't been noticeable to me. At 200 and further it is to the point where I'll add some compensation (0.2 @200, 0.3 @ 300, 0.4 @400, 0.5 @ 500) otherwise you seriously start to question your wind holds. I'm also a T1x shooter (16" bbl 1:16.5" right twist).
 
#8
Your bore could be slightly off center so that it is adding what looks like an induced wind. OR the scope is not parallel to the bore. Something is canted

Do this. Zero at 100 yards and then go back to 50 yards. If the bore and the scope are not parallel then the 50 yard zero will be 1/2 of what you saw at 100 before and to the left. That would definitely show that the bore and scope center line are not parallel.

The suggestion about canting could be it also but I think to get that much the cant at 100 yards would be so noticeable.

David
 
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#9
guydudeman said:
I am grouping well at both 50 and 100 yards. My point of impact is dead on at 50 and punching one hole. At 100 yards I am my point of impact is .1 mil right of point of aim. Is this a normal amount of spin drift?
Click to expand...
Cant in either or both the rifle and the scope can easily explain a change in POI between 50 and 100. At the same time, if it doesn't happen repeatedly on all range trips, it could be caused by wind. In any case, a .1 mil POI difference is not great.
 
#11
This has been over 3 range trips. I don't have a kestrel but I don't feel any wind walking down to set up targets.

I did dial the 100 yards to zero and checked at 50 yards for windage. It was exactly 0.1mil left at 50. I did not measure distance. I just used the reticle to get angular measurement in mils.

I do have an bubble level. I use the "real avid level right pro" to level my scope/reticle.

I will be testing again this weekend.
I will try hold over to see if it's differnt. Then I will box test the scope with plumb line.

.1mil might just be the spin drift for 100 yards. My calculator says .04 but my inputs are no accurate so I don't really trust this anyway.
 
#12
I wanna see your paper targets for your next trip.

.1 mil right sounds like its inside your groups natural dispersion. 1 MOA groups (which is highly common at 100yds) is 0.3 mils in size and most can't hold 1 MOA even with good gear over 10 shots.

I shoot in a bermed range. We have a 50/100 bay, another 100 yard bay, a 200yd bay, and a 300yd bay.

There is ALWAYS wind on our range. The berms don't block the wind. It funnels it.....and very unnaturally compared to a wide open field.
Screenshot_20240906_194300_Maps.jpg


When the grass is mowed low, the sun heats the ground, and no wind flags are posted....its very difficult to guage wind speed and direction at times. We've had multiple stages in a single bay and it's not uncommon to see stage 1 on the far left to be right hold....stage 2 in the center to be no wind hold....and stage 3 on the far right being a left hold.
Screenshot_20240906_194318_Maps.jpg
 
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#14
50 yard and 100 yard targets. 10 round groups

I would say the horizontal stringing is my skill deficit and the vertical is more indicative of what the rifle is capable of. On the 100 yard group I have ignored the bottom flyer in my measurement because I slapped the trigger and I knew it right away. Still doesn't change the center. Still 3/4 to 1 inch right at 100.

I can accept this but I will continue to investigate. How would I accurately measure the more center and scope tube to see if they are parallel?
20240907_102001.jpg
20240907_102041.jpg
 
#15
The difference in impact between 50 and 100 yards?

Windage

Localized turbulence due to thermals or adjacent range features

Precession and nutation affecting the trajectories.
Bullets rarely travel a simple arc.
They spiral around the initial fight path.

Scope related alignment or parallax issues.

Recoil shift in barrel alignment compensated for at 50 yards
by the scope settings, but showing up at 100 yards.

Have I forgotten anything?
 
#19
One mil at 100 yards is about 3.6". A tenth of a mil at 100 is about 0.36". One MOA is close to one inch at 100.

Wind isn't always even between shooter and target. There can be more wind closer to the target than the shooter, or vise versa, or a mix of things in between. This means there could be more wind past 50 yards than before it.

Cant of the scope/rifle can explain what's shown by the OP. It can be one or more of the combinations shown below.

 
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#20
guydudeman said:
Hi

I am fairly new to precision rimfire.

Tikka T1x. Arken sh4. Sk match ammo.
50 yard zero. Area 419 20moa rail. Arken rings

I am grouping well at both 50 and 100 yards. My point of impact is dead on at 50 and punching one hole. At 100 yards I am my point of impact is .1 mil right of point of aim. Is this a normal amount of spin drift?

The range I shoot at has large berms along the side and gets almost no cross wind. Testing has been on multiple days at very calm weather no perceived wind.

I am just wondering if this would be a normal amount or if I should be looking at my scope mount or other setup issues.

I use this for prs rimfire matches
Click to expand...
There will be some spin drift at 100yds. You may have some wind also. I was at the range yesterday. There was no wind at the bench, it may be a good day for no wind. I shoot steel at 200yds and 300yds. I started at 200 yds. I was having to hold 0.5 mils for wind. At 300yds it was a full mil. As you go out in yardage, you will see this more and more, due to spin drift, wind, and weather conditions. I check my Ballistic app many times a day, for changes in the weather.
 
#21
When I see a shift like that, it is almost always a “natural point of aim” problem. Consistently .3mils at 100 when the wind is not always identical trip to trip, means bad position in some way. When I correct my shooting position, yes, including on the bench with a 17lbs 22LR, the group goes back to the Center.
 
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#24
HMRamateur said:
Just trying to rule out wind for sure... does the wind travel the same direction as your bullet, even though there are berms there? 100y is still a decent ways for a 22lr to travel and not be affected by the wind, however small it is. And just because there are berms doesn't mean there isn't still air movement below them.
Click to expand...
Berms can actually cause really weird wind. Depending on the layout and wind direction it could cause all different types of drafts.

For example a cross wind will follow the terrain which will cause the wind to go up, down, and then up again.

It also can cause temperature variables, again depending on the circumstances.

Whether or not any of that has any influence at 100 yards with a 22LR...I don't know.
 
#25
Is the center line of the retical center to the bore ? All can be level but if the center line is off you can sway one way or the other.

I would ajust the 50 yard to the left a tenth or so then redo the 100 yard. It seems to be to the right.
 
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