Rifle Scopes Signs of a canted scope?

[Wheres-Waldo]

Hey guys, I wanted to ask about an issue I have when going from one range to a further range, and dial in my elivation.

Typicaly when I input elivation, I dont touch windage, as one shouldnt have to, unless conditions require.

BUT, the further out I go, the further to the right my POI shifts. Is this a sign of a slightly canted scope, or a tendency to cant the rifle during fallow through?

I have a Horus Vision ASLI on my rifle, and have leveled my scope via the feeler guage method, but I could imagine a slight amout of error in that.

The entire unit was leveled with the shitty "Level Level Level" Wheeler deal, on the bolt raceways before the ASLI was put on.

Any comments?

 

[45.308]

Re: Signs of a canted scope?

I chased POI right for months; me, wind or ???. I was told and always thought it was me or the wind but I wanted to get my scope / rifle perfect first. No use chasing multiple gremlins.

I hung a 3mm thick black pcord with a heavy weight on the end on a 48" tall cardboard target at 100 yards. I could tell by the top mildot, it was a strain to see, my scope was ever so slightly twisted CW when my ACD was bubbled level. I put a shoot-n-c paster dot at the bottom of the cardboard cut center by the pcord. At 36moa up I placed another paster cut center by the pcord.

Shot 3 rounds at the lower dot, cut center. Doped in 36moa which is 1000 yards and I was well over 3" to the right. Back to 100 cut center and back to 36moa with same results. So I twisted my scope so the top mildot cut center with the string, shot and now I was about 1" or so still to the right. Using a pencil mark on the rings and scope for reference, rotated scope slightly until I cut center 100 and cut center doped 36moa with ACD bubble level. Shot a group on a 5" shoot-n-c at 350 yards, it was centered vertically on the target, finally. I now have no issue with all groups always POI right. Not that I do not make shooting errors but I know my rifle and scope are perfect so any issue now its not the rifle / scope.

Hope this helps and good luck!

 

[Wheres-Waldo]

Re: Signs of a canted scope?

Thankyou 45.308 (still trying to wrap my head around the entire process though)

I called the local gun-shop and told them my rifles symptoms...
First thing he suggested? "Oh, your rail mt. holes in your reciever are off center."

.....This doesnt even make sense does it? Theoreticly if they were off center, and my scope was level...I could bring the POI on target, and end of story....

I let him know that I'm running a trued action, and that I could much more easily see it being a scope canting issue.

I dont have axcess to anything short of what you would concider feild conditions....

I may have to PM you 45.308, to see if I can better understand this process.

 

[Graham]

Re: Signs of a canted scope?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Wheres-Waldo</div><div class="ubbcode-body">BUT, the further out I go, the further to the right my POI shifts. Is this a sign of a slightly canted scope, or a tendency to cant the rifle during fallow through?</div></div>If you are shooting groups good enough to diagnose a canted scope, then I'm impressed.

Canting during follow-through probably won't acheive anything that isn't there when you fire the shot. That is, unless you are slapping or crushing the trigger.

What do you mean by "further out?" and what do you mean "further to the right"? If you are dialing a few right adjustments at 1000, then maybe. But my best guess is that it's you, yanking the trigger.

 

[glock24]

Re: Signs of a canted scope?

http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/ScopeChecking/

 

[clmayfield]

Re: Signs of a canted scope?

Here are some calcs for cant for a standard .308 running FGMM. Cant varies by drop, so if you are running faster, cant makes less of a difference, if you are running slower, it makes more difference.

range 1 deg 2 deg
yds inches inches
100 0.07 0.14
200 0.22 0.43
300 0.48 0.96
400 0.89 1.77
500 1.46 2.92
600 2.24 4.47
700 3.26 6.52
800 4.59 9.18
900 6.29 12.57
1000 8.43 16.85

As you can see, cant doesn't start making a real difference until 500 yards or so. You can probably see 2 degrees of cant. 1 degree of cant is hard to discern.

After doing the RO trigger school on this sight, I realize that a lot of my windage error is from poor trigger control. It doesn't show up much at close distances.

If you have a cant problem, an anti-cant will fix it easy enough. It is practically a must at longer distances, for me at least, but I am really bad at discerning cant.

 

[45.308]

Re: Signs of a canted scope?

I forgot to add the precursor to my POI gremlin for those who want to know. I used a Wheeler Level Level to mount my SS. I used 3 different ones and they all had different bubbled level. Only when I starting out past 100 yards did I realize how far to the right my POI was. I could not a hit a 5" shoot-n-c at 300 when I first started chasing. I kept playing with the Wheeler trying to average between the three.

Then someone here sent me an ACD (a sincere thanks) and when I mounted it something looked funny. With the ACD bubble level, the hairs were way canted. I leveled the ACD with tin foil to match my SS, stupid idea.

So, I decided to start over and used LL feeler gauge method and instantly I hit the 5" target, still to the right though but happy. Thinking it was perfect I left it for a while but got frustrated and did the pcord method and found out feeler gauge was only off a bit. My ACD has no tin foil under it now and POI right always always always right is gone. Not that I do not make mistakes but that is my point now, my SS was canted and it is perfect now so when I do, I know its me which has eliminated my frustration.

And, using the Wheeler Level level once I pcorded leveled it all, it was a full bubble off of level, bubble did not touch the centering lines. I took them all back and got my money back.

 

[Rancid Coolaid]

Re: Signs of a canted scope?

Wouldn't a scope with a CW cant throw rounds left - since any change increase elevation would also push the reticle to the right, throwing rounds low and left?

Can't argue with results, but... gravity sucks.

 

[Wheres-Waldo]

Re: Signs of a canted scope?

I would use the feeler guage method, but my rail, although a 1 peice, is relieved in the middle....

I took everything off last night...

I leveled the rifle...then put the rings on and made sure the bottom halves still read level. Set the NightForce in and leveled the top cap, and toqrued everyhting to spec.

Im sure my POI will shift significantly, but as long as she's on straight I dont care.

This week-end Im gonna mount a plum-bob out at 100 and see how it tracks...

Im thinking a poster-board turned vertical with targets every few MOA, keep the same POA, and dial in a few MOA per shot...and see where my impacts land me once I have in 20-30 MOA.

And Rancid....I was thinking low-left myself..more left than low though?

What is PCord leveling?

 

[Greg Langelius *]

Re: Signs of a canted scope?

Zero at 100. Run the elevation up 30 MOA and shoot 3 shots ( one assumes you have about 3ft of white target paper above your aim point). Drop a plumb line from the bullet holes down to the aim point. If the line passes through the aimpoint, you're plumb. If it passes left of the aimpoint, you need to rotate the scope clockwise to correct. and vice-versa if it passes right. And if I got it backward, I'm an ass, but all you gotta do is opposite of what I said.

message ends...

Greg

 

[Wheres-Waldo]

Re: Signs of a canted scope?

Even easier.

Thanks Greg

 

[N2rockets]

Re: Signs of a canted scope?

This might help!

http://www.riflescopelevel.com/cant_errors.html

Pretty easy to see if canting is the real issue. Lots of good information here.

 

[wksinatl]

Re: Signs of a canted scope?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Carter Mayfield</div><div class="ubbcode-body">Here are some calcs for cant for a standard .308 running FGMM. Cant varies by drop, so if you are running faster, cant makes less of a difference, if you are running slower, it makes more difference.

range 1 deg 2 deg
yds inches inches
100 0.07 0.14
200 0.22 0.43
300 0.48 0.96
400 0.89 1.77
500 1.46 2.92
600 2.24 4.47
700 3.26 6.52
800 4.59 9.18
900 6.29 12.57
1000 8.43 16.85

As you can see, cant doesn't start making a real difference until 500 yards or so. You can probably see 2 degrees of cant. 1 degree of cant is hard to discern.

After doing the RO trigger school on this sight, I realize that a lot of my windage error is from poor trigger control. It doesn't show up much at close distances.

If you have a cant problem, an anti-cant will fix it easy enough. It is practically a must at longer distances, for me at least, but I am really bad at discerning cant. </div></div>

OK Carter I'll throw a wrench in the works. I know you are talking centerfire but.........if you were shooting rimfire at longer distances would it still not be a big deal. Being you have cranked in more elevation instead of just distance would that not matter? If a 22 is dead nuts on at 50yds and you add 25moa to the scope wouldn't it still throw it WAY off becasue of the scope adjustments more so than distance to the target?

I hope you know what I'm asking. I'm not even sure if I know what I'm asking????

Seems like Greg's way takes this into consideration.

I'm not saying you are wrong just tryin' to understand.

thanks,
Keith

 

[Buckoman]

Re: Signs of a canted scope?

Ok here something that's a different possibility. I talked to Vern Harrison about a year ago in regards to which gear, gun barrel, bla bla bla. The one thing he suggested for me was a 1:12 twist barrel because the higher the twist, the more centrifugal drift occures downrange.

So, in my response, could this be a possibility as to this gentleman's issues?

 

[Wheres-Waldo]

Re: Signs of a canted scope?

Master, I appreciate the insight.

Im gonna contribute the issue to just flat out plain ole "scope wasnt level"

Ive leveled everything and mounted a NEW Horus Vision ASLI.
According to Wikipedia, as I'm not nearly well versed on external ballistics, spin drift would lend to an inaccuracy of only about .7 MOA at 1000 yards.

Ide imagine this effect would decrease exponetialy as the range decreased, but then again, I'm pretty much guessing.

 

[clmayfield]

Re: Signs of a canted scope?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KS</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Carter Mayfield</div><div class="ubbcode-body">Here are some calcs for cant for a standard .308 running FGMM. Cant varies by drop, so if you are running faster, cant makes less of a difference, if you are running slower, it makes more difference.

range 1 deg 2 deg
yds inches inches
100 0.07 0.14
200 0.22 0.43
300 0.48 0.96
400 0.89 1.77
500 1.46 2.92
600 2.24 4.47
700 3.26 6.52
800 4.59 9.18
900 6.29 12.57
1000 8.43 16.85

As you can see, cant doesn't start making a real difference until 500 yards or so. You can probably see 2 degrees of cant. 1 degree of cant is hard to discern.

After doing the RO trigger school on this sight, I realize that a lot of my windage error is from poor trigger control. It doesn't show up much at close distances.

If you have a cant problem, an anti-cant will fix it easy enough. It is practically a must at longer distances, for me at least, but I am really bad at discerning cant. </div></div>

OK Carter I'll throw a wrench in the works. I know you are talking centerfire but.........if you were shooting rimfire at longer distances would it still not be a big deal. Being you have cranked in more elevation instead of just distance would that not matter? If a 22 is dead nuts on at 50yds and you add 25moa to the scope wouldn't it still throw it WAY off becasue of the scope adjustments more so than distance to the target?

I hope you know what I'm asking. I'm not even sure if I know what I'm asking????

Seems like Greg's way takes this into consideration.

I'm not saying you are wrong just tryin' to understand.

thanks,
Keith </div></div>

Yes, a rimfire will need an anti-cant device for anything over 50 yards and it would be a good idea at 50 yards. I am not talking about scope zeroes, I am talking about actual drop if the gun were aimed exactly horizontal. What you do to zero a scope is you move the vision path (I don't know the technical term) downward to compensate for bullet drop.

When you cant the scope, rather than this path going straight down to adjust for gravity, it moves down and to the side. As a result, it undercompensates for gravity and over compensates on the horizontal (windage). The numbers above are not precise. All they are is the Sin of the cant angle times the amount of drop if the bullet started with a flat trajectory.

With a 22LR, the effect of cant is as follows:
range 1 deg 2 deg
yds inches inches
50 0.10 0.20
100 0.32 0.65
150 0.73 1.46
200 1.34 2.67
250 2.16 4.33
300 3.24 6.47

I am not really trying to counter Greg's way... Greg's idea is right... I was just pointing out the effect of cant. For centerfire at shorter distances, it is miniscule. At longer distances, it starts to make a difference. For rimfire, it makes a difference at almost all ranges; it just depends on the drop for whatever bullet you are using.

I was just trying to quantify how far off you are. If you are playing at longer ranges, buy an anti-cant device, mount it to your scope, and center it to the scope using a plumb bob. Some people mount to the pic rail, but I think you are taking too many leaps of faith about things being square. If you mount directly to the rail, the reticle needs to be square to the scope, the scope needs to be square to the rail, and the ACD needs to be square to the rail. Little errors in all of these can start to add up.

 

[wksinatl]

Re: Signs of a canted scope?

Thanks Carter. It looks like it makes a significant difference.

Keith