External ballistics question about non wind-induced drift....slugs specifically.
- Thread starter Franklink
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There is nothing scary about barrel indexing, in fact, I once ev
/gets swallowed whole by a T-Rex, before finishing the forum post/
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Barrel indexing is a completely different ball of wax. Most of what was discussed here was spin drift and/or rotating the scope in the rings to align vertical crosshair with the barrel/bore.
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Barrel indexing could do the same thing as rotating the scope in the rings depending on how crooked the bore is. None of them are straight....which is why I don't use the mirror method.
Mike
Mike
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I've had/have a couple guns that allow barrel indexing and yes it's very interesting to watch the impact point rotate around "center" as the barrel is clocked.
In this particular gun, that's not an option as a potential way to make everything line up. The transfer port is cut into the barrel on this one.
(And spin drift and scope cant were the topics mostly discussed thus far-hence barrel indexing being a whole different ball of wax).
In this particular gun, that's not an option as a potential way to make everything line up. The transfer port is cut into the barrel on this one.
(And spin drift and scope cant were the topics mostly discussed thus far-hence barrel indexing being a whole different ball of wax).
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The more I've (over) analyzed this, seems that between crooked bores, actual versus what feels "square" in the sight picture, spin drift, etc? I might be best served by simply accepting it for what it is and dealing with it (like I was doing all along lol).
At this point, it'll be interesting and maybe educating to see what effect rotating the scope in the rings has, compared to what I've been seeing. But I suspect that after a shooting session I'll want to go back to what feels square to me when looking through the scope. And that's mostly b/c what we're talking about here is a small percentage of the shots taken. Most shots won't be at these extreme (for fpe) distances.
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I would ,first, verify that the gun poi has been fixed by the mirror method. I don't remember you saying it was fixed, but haven't been following closely.
Adjusting the scope using the method I described takes nothing for granted. It will yield a perfect result every time...even if the barrel bore is not straight.
Adjusting the scope using the method I described takes nothing for granted. It will yield a perfect result every time...even if the barrel bore is not straight.
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No Mike, haven't had a chance to see what effect rotating the scope via mirror method has. I've been working all week.
With your method, looks like between 6 and 7 yards would be the same clicks as the 175ish. It'll be easy to do that comparison as well, the next chance I get to do some shooting. Since I messed with the scope in the mounts, I'll have to verify scope zero first.
With your method, looks like between 6 and 7 yards would be the same clicks as the 175ish. It'll be easy to do that comparison as well, the next chance I get to do some shooting. Since I messed with the scope in the mounts, I'll have to verify scope zero first.
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You have to get your zero and your 6/7 yard to fall exactly on the center of a plumb line. If your scope doesn't focus to 6/7y....just use the 6-7y clicks and shoot it at whatever the closest your scope will focus. I've always done the procedure at my zero and 10y. Every time you rotate the scope you should recheck your zero. If you are landing to the right on your short distance, you will rotate the scope ccw from behind. It's actually been a while since I set up a ft gun...but I think I'm saying it right.
Mike
Mike
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I may be wrong, but I believe you must have your zero correct anyway...even when using the mirror method.
Mike
Mike
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It was zeroed when I did the mirror trick and found bore to be right of vertical crosshair. So I rotated the scope in the rings to make vertical bisect the bore. Next step (I think) is to see what that did to scope zero.
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I think you are right unless your zero happened to be on the optical center of the scope. I think you would also have to redo the mirror procedure if the zero has moved. But again....maybe I'm wrong.
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When you rotated the scope, did you do this with the scope at 6x or 24x? Just curious if changing the magnification makes a difference to bisecting the bore. Or checking with the scope zeroed at say 40yds..then clicking up to the 174yd setting..still bisecting?
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Regardless of the rail elevation factor, what do you do with the windage turret during the mirror method? Adjusting that will also change how the vertical retical intersects the bore, and could be used to center it, vs rotating the scope. So would you want it optical center and then never touch it except to dial for actual wind?
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I was doing the mirror experiment with 24 and 16x, the two most used magnifications. Going between 24 and 16x didnt change the relationship between vertical reticle and barrel bore.
I did not add in the clicks for 174yards to see what it would do to the crosshair/bore relationship. The vertical turret adjustment was at the zero stop for all of the mirroring.
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The problem with optical center of a scope is that it rarely agrees with impact point. So even if optically centering for the mirror trick, a guy is going to have to UNoptically center to get the scope zeroed. I understand there are adjustable scope mounts, but that's a potential for slipping out of adjustment that I just don't want to deal with.
There has to be a starting point, the scope was zeroed for the initial mirror-ing. I'm guessing it'll need some adjustment to be rezeroed now that I rotated it ever so slightly. I'll recheck the mirror after rezeroing to see if crosshair still bisects the bore.
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@Franklink the relative rough position of the windage turret when zeroed by shooting might still be indicative somehow (this could be hard to know).
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Spent the last 2 hrs playing scope cant versus rifle can't versus true vertical versus perceived vertical.
By the time I got it how I want it I had all kind of stuff spread across my back yard. Plumb bombs hanging from the bug light Shepard's hook, pellet traps at 10, 30, and 55yards. Cardboard boxes with vertical lines drawn on them at 7 yards and 55 yards, mirror @ 15 feet, I even had the 3foot bubble level out to make sure those vertical lines in the cardboard were vertical....this endeavor isn't for the faint of heart.
Hoping the semi-decent wind conditions hold for me to stretch it out further but at this point I've reached some conclusions.
1st. The mirror isn't the end all, be all. Vertical is very different from perceived vertical at close ranges like used for the mirror.
2nd. I was running in circles til I hung the plumb bomb.
3rd. Seems that a combined process of going back and forth between the plumb bomb, the mirror trick, the bubble level on the gun, and taking shots in paper at near, zero, and far distance (7, 1
0, 30 and 55 in this case) is necessary.
Essentially I had over-rotated (counter clockwise) the scope in the rings the other night in the living room. I had to come back some (clockwise) to still bisect the bore, while keeping the vertical crosshair truly vertical.
And yes, even the slightest rotation in the scope rings messes up the scope zero.
So right now I'm zeroed and at a point that I could shoot a <55yard ft match and probably do well.
Now on to heavier pellets and slugs and further yardages.
By the time I got it how I want it I had all kind of stuff spread across my back yard. Plumb bombs hanging from the bug light Shepard's hook, pellet traps at 10, 30, and 55yards. Cardboard boxes with vertical lines drawn on them at 7 yards and 55 yards, mirror @ 15 feet, I even had the 3foot bubble level out to make sure those vertical lines in the cardboard were vertical....this endeavor isn't for the faint of heart.
Hoping the semi-decent wind conditions hold for me to stretch it out further but at this point I've reached some conclusions.
1st. The mirror isn't the end all, be all. Vertical is very different from perceived vertical at close ranges like used for the mirror.
2nd. I was running in circles til I hung the plumb bomb.
3rd. Seems that a combined process of going back and forth between the plumb bomb, the mirror trick, the bubble level on the gun, and taking shots in paper at near, zero, and far distance (7, 1
0, 30 and 55 in this case) is necessary.
Essentially I had over-rotated (counter clockwise) the scope in the rings the other night in the living room. I had to come back some (clockwise) to still bisect the bore, while keeping the vertical crosshair truly vertical.
And yes, even the slightest rotation in the scope rings messes up the scope zero.
So right now I'm zeroed and at a point that I could shoot a <55yard ft match and probably do well.
Now on to heavier pellets and slugs and further yardages.
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Interesting discussion...
I haven't seen it mentioned but you said you were adjusting the elevation to shoot at the very long ranges. If the windage adjustment isn't perfectly centered ( maybe even if it is), the poi will move laterally as you approach the limit of the scope. If you can secure your rifle well enough, you should be able to see the tracking drift against a vertical line when approaching the limit.
I really appreciate the selection of good, adjustable mounts today as we had lots of those type issues early on in our ft journey with 1" tubes and poor barrel/ receiver alignment.
Bob
I haven't seen it mentioned but you said you were adjusting the elevation to shoot at the very long ranges. If the windage adjustment isn't perfectly centered ( maybe even if it is), the poi will move laterally as you approach the limit of the scope. If you can secure your rifle well enough, you should be able to see the tracking drift against a vertical line when approaching the limit.
I really appreciate the selection of good, adjustable mounts today as we had lots of those type issues early on in our ft journey with 1" tubes and poor barrel/ receiver alignment.
Bob
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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+
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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...
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