External ballistics question about non wind-induced drift....slugs specifically.

[Ranchibi]

I have been using this gizmo for a few years and it seems to work very well. I’m not a competitive shooter, outside of biathlon, but my Pantheras hold up at 100+

Level-Right® Pro

ACCURATE SCOPE MOUNTING MADE EASY A level reticle is critical to long range Accuracy. For longer shots a canted (or unlevel) reticle will pull or push the bullets trajectory off of vertical center. It gets worse the further the distance increases. A level scope means that the reticle...

www.realavid.com

I somehow understand how this alignment tool(s) works........will probably pick one up! Works like a plumb bob and lets one know if the barrel is aligned with reticle.

 

[bigHUN]

 

[JungleShooter]

I did not read all the replies so sorry if it was mentioned before.

With right-hand twist barrels, bullets and slugs will spindrift to the right. Pellets will spindrift to the left. I had the same query but then read on a few websites about it. I don't have LINKS now so you can do a search.

Here is a LINK!

By ballistician Miles Morris, on HardAir Magazine's forum:

Spin Drift

Following a recent question and discussion on spin drift for slugs, I was asked if I could post this old thread from a UK forum. I wrote it for sub 12FPE guns using pellets, so the speeds are low and slugs are not considered. The general effects are the same at high speeds and for slugs. The...

community.hardairmagazine.com

 

[dgeesaman]

Wow that scope leveling tool is way fancier than my Wheeler Engineering reticle leveling tool. It would seem they do the same thing though.

 

[thomasair]

Use either scope leveling tool and it may or may not work. It takes some things for granted. After being burned by the wheeler long ago ...I switched to the zero and near distance method I already described. It never fails because you are actually using poi results to align your reticle. The mirror method has failed me as well.

Mike

 

[beerthief]

Use either scope leveling tool and it may or may not work. It takes some things for granted. After being burned by the wheeler long ago ...I switched to the zero and near distance method I already described. It never fails because you are actually using poi results to align your reticle. The mirror method has failed me as well.

Mike

zero and near distance method I already described . where please , it is not in this thread . Thanks Stan

 

[thomasair]

Post 13....but additional info after.

 

[bigHUN]

I am using that my diy 3d printed tool to set the bubble only.... and btw me shooting of the bench only so with consistency I am on safe side.
My Impact MK2 has a "floating" picatiny rail, after every deeper surgery I must do the 20 <-> 100 drill there and back until it hits the same vertical.
But lucky me, after a year or so playing FX mechanic finally I settled with a fixed distance/amo and didn't had to move that rail since last summer
A good learning curve tho, you folks shall taste it

 

[EBREWER]

If all the pellets are grouping at the same location to the right I have a hard time believing the scope cant issue. the shorter ranges would typically be to the left in that instance. Coriolis effect at 100 yards is hard to believe.

 

[Franklink]

Stretched it back out yesterday evening (171 yards this time).

This is after the mirror trick, and the shooting close trick, and the plumb bomb trick, and the etc etc etc trick. Readjusted the bubble level on the gun so that I know when the bubble level is good, my vertical crosshair is truly vertical.

So, first shot @ 171 drifted right again, off the paper. Maybe 12-15inches? and only basing that on the fact that it hit that woven wire fence (like it did the first attempt at 170+ a few weeks ago) and threw some shrapnel back into my cardboard. I did see the woven wire vibrate when hit, but hard to pinpoint exactly where hit. Adjusted it to the left so that I could shoot my groups. Wind was pretty dang minimal. Very slight headwind, and only on some of the shots. I'd guess most shots were no wind, but I could feel a gentle push straight in from the target on some of the shots, couldn't have been more than 2-3mph at it's peak, and it wasn't peaking very often.

I think spin drift.

 

[Scotchmo]

Stretched it back out yesterday evening (171 yards this time).

This is after the mirror trick, and the shooting close trick, and the plumb bomb trick, and the etc etc etc trick. Readjusted the bubble level on the gun so that I know when the bubble level is good, my vertical crosshair is truly vertical.

So, first shot @ 171 drifted right again, off the paper. Maybe 12-15inches? and only basing that on the fact that it hit that woven wire fence (like it did the first attempt at 170+ a few weeks ago) and threw some shrapnel back into my cardboard. I did see the woven wire vibrate when hit, but hard to pinpoint exactly where hit. Adjusted it to the left so that I could shoot my groups. Wind was pretty dang minimal. Very slight headwind, and only on some of the shots. I'd guess most shots were no wind, but I could feel a gentle push straight in from the target on some of the shots, couldn't have been more than 2-3mph at it's peak, and it wasn't peaking very often.

I think spin drift.

Spin drift won’t be 12” at 171yd. Maybe a couple of inches. 3mph wind could do it with a pellet or low BC slug.

 

[Franklink]

Spin drift won’t be 12” at 171yd. Maybe a couple of inches. 3mph wind could do it with a pellet or low BC slug.

The "I think" part of that was b/c all the scope futzing didn't resolve it.

Dunno the exact reason, but rightward drift is pronounced. Wind flags at 30 and 100 yards were hanging straight down for a good percentage of the shots, could just barley feel a hint of "wind" coming at my face during this session , and only on some of the shots. I'd call it more of a thermal rolling up and out of the creek than wind.

What tiny hint of wind I had the last time on paper at this same location was from behind me. So two completely different winds, and rightward drift for both sessions.

In various locations at various pdog towns over various days and various directions, impact point always further right as distance increases. Zero for 60 yards is not impacting right of aim point.

It just does it, very predictably, which is the best kind of DOPE to account for (the predictable kind).

 

[fisherhunt3]

The drift doesn't seem to be a stability issue, because they're consistently drifting. Ie I can make em go where I want, if I account for that drift like I account for trajectory arc. Seems if they were losing stability the impact points wouldn't be reliable.

But your underlying implication that slower may drift more is interesting.

Slower fps= more flight time so more time to drift at least that's my theory

 

[thomasair]

If you rotated your scope significantly as you implied....it's not possible that you can obtain the same results unless something else has changed.

Which way did your scope end up turned compared to your original setting?

Mike

 

[Franklink]

If you rotated your scope significantly as you implied....it's not possible that you can obtain the same results unless something else has changed.

Which way did your scope end up turned compared to your original setting?

Mike

Hard to say with absolute certainty b/c I messed with the scopes orientation in four different sessions, spread over the last 10ish days.

First big adjustment was scope going counterclockwise, from shooter position. That was an overadjustment so in the second futzing I went back clockwise maybe 1/2? of the first first rotation. Third and fourth adjustments werent as big of rotational jumps.


The "best" combination of mirror test, close and far impact points, and the plumb bomb puts the rifle canted quite a bit more than it was before all of this craziness. It seems the rifle MUST be canted to get the scope at true vertical while also keeping impact points intersecting s vertical line at near and far (55yards) distances.

Just before the recent 171yards session with slugs, I shot 10, 30, and 55 yards with the sub20fpe tune (pellets, not slugs) and the impact points are lining up on the vertical at those three distances. This was using the scopes same orientation from a few days prior (4th scope futzing).

I'm not touching it again. It does what it does, impact point drifting further and further right as distance increases.

 

[thomasair]

Whether or not you intend to change it, I think it's important to understand the reason it's happening. It's certainly not spin drift accounting for the bulk of your error.

Mike

 

[Franklink]

Whether or not you intend to change it, I think it's important to understand the reason it's happening. It's certainly not spin drift accounting for the bulk of your error.

Mike

I agree. I'd REALLY like to understand what's causing it.
That was the intent I had in starting the discussion.

 

[lbc_PSI]

I assume you’re clicking to the 171yds distance? Do you get the same amount of drift when using hold-over?

Have you tried switching to a different scope or rings? Same results?

Is the scope FFP? Have you tried a SFP scope?

Does the same drift occur with all projectiles you’ve tried?

When you’re clicking to the further distances, is there a point when the drift begins or is it gradual? How close to the max click travel are you? Could the erector tube be coming in contact with something inside the tube?

Grasping at ideas…

 

[Franklink]

I assume you’re clicking to the 171yds distance? Do you get the same amount of drift when using hold-over?

Have you tried switching to a different scope or rings? Same results?

Is the scope FFP? Have you tried a SFP scope?

Does the same drift occur with all projectiles you’ve tried?

When you’re clicking to the further distances, is there a point when the drift begins or is it gradual? How close to the max click travel are you? Could the erector tube be coming in contact with something inside the tube?

Grasping at ideas…

Great ideas.

Scope is a ffp. I own sfp scopes but have not tried to swap out the scopes or the rings.

With how much further pellets get pushed by wind at these distances, it's hard to say if the same thing is happening with pellets. @ 100 yards the slugs ARE already drifting to the right of the impact point of pellets, bout 1 to 1.25"

Drift seems gradual, as distance increases so does drift.

I'm quite a ways from max travel, clicks were between 76 and 80 clicks on the most recent session. I'm away from home to check right now but from memory I've got 100 clicks per revolution with this scope. Seems like I can remember getting about 180 clicks of elevation before it bottoms out (tops out?) but again, I'm away from home and only going off memory.

 

[JDGriz]

It is possible that the reticle part's vertical line is not perfectly aligned with the vertical travel direction of the inner scope tube. However if this was the case, there would be equal ammounts of MOA POI shift in the other direction at distances below the zero(ed) distance. Or maybe it moves in a slight curve at extreme click amounts.
A different scope or a jack plate arrangement with the same scope might settle it. Or using holdover.

Actually, you could just check how well the scope zero traces a plumb bob line from 0 to 100 clicks down (with a clamped down rifle or just the scope).