The Effects of Scope Cant

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Saw this over at the Hide and I finally found it again. Figured it was good info to share with you guys. Not sure if it was posted yet

I drew up a file in autocad with 1" thick bars running horizontally across a 36" wide piece of paper. The top bar was canted 5° right, the middle bar was level, and the bottom bar was canted 5° left. My intent was to match my reticle to the thick black bars (thus canting my rifle 5° left or right) and to use the 6" orange circles in the center for my aiming point.

The top left aiming point was to get my zero. The top right was to run a 5 round test group after verifying my zero so I knew whether or not I could proceed with the test. I wasn't going to go ahead if I was shooting like s**t... this target has been riding around with me in my truck for three weeks waiting for a good opportunity to get pasted.

Test platform:
AI AE mkII - 24" barrel
Atlas Bipod on AI Spigot
Premier Heritage 3-15x50 on AI 45MOA base/rings
Sight height over bore = 2.3"
Load: 155 scenar at 2900fps.
39°F, 29.35 inhg, 50% humidity. Wind variable from 4-6 o'clock at 2-6mph.

Now I know you're going to say that 5° is a lot of cant, but it was done this way because I have a very controlled enviroment to shoot in at 600yds and didn't want to increase the range just so I could decrease the cant and my comfort. I would go further and say that I don't actually think 5° would be all that unlikely if someone was shooting in a position off of a sidehill (or you name it scenario) and didn't have any good references to find level.

Setup
001_web.jpg


Shooting
002_web.jpg


Results
003_web.jpg


Results:

The top group aggregate measurement from centerline is 10.3" right (group measures 6-1/4")

The middle group is right on centerline (group measures 2-7/8")

The bottom group aggregate measurement from centerline is 8.1" left (group measures 4-7/8")

Note: There is a small hole just low-left of the 5° right canted orange aim-point. This is a bullet fragment from the steel we were shooting after the test.
Click to expand...
 
I wonder if all the people that posted in another thread, not too long ago (scope level thread maybe), that said scope cant doesn't make a difference will get the picture now.
 
CyaN1de said:
I wonder if all the people that posted in another thread, not too long ago (scope level thread maybe), that said scope cant doesn't make a difference will get the picture now.
Click to expand...


Thats the reason I went crazy looking for that article. It does make a difference but only when you really get out there...pictures dont lie :D
 
This is why there are the various bubble level devices.
You can't cant.
The greater the range, the more critical it is.
 
I hope all the naysayers have a look. Great way to illustrate the reasons for not canting. I guess a picture is worth a thousand posts!
 
The higher the scope is above the axis of the bore, the more important it is not to cant the rifle.
Some of the chassis systems require a really high scope mounting.
 
Good work; looks like a well-designed and well-run experiment. The guy knows how to shoot well too (half-minute verticals at 600 yards for all three groups).

FWIW the theory predicts a 5 degree cant will produce a 7.7" (1.2MOA) displacement under these conditions. It looks to me like the theory agrees with the holes in the paper; it's always nice when that happens!

To the extent that you trust the theory, it predicts that the same 5 degree cant will produce a 28" (2.7MOA) shift at 1000 yards for this ammo.

I might be one of the people being thought of as a "naysayer" but I don't think that's necessarily true (what I was saying, and what I still say, is that in most cases a scope shooters doesn't need a bubble level rather his reticle alignment is good enough. And my other point was that the cant of the scope relative to the rifle is immaterial, the important factory is that the scope cant relative to the target level be kept consistent)

Now while choosing 5 degrees was a good choice for this experiment, under shooting range conditions it a visibly-obvious error that a shooter firing in competition will not willingly make. Shooters should have a look at the third picture in the first post and estimate what fraction of that angle they'd be able to detect in shooting conditions. If you think that by visual reference between your scope reticle and the target frame you could hold your cant error to no more than one-fifth of that, then that means you could expect a horizontal error due to cant to be no more than 1.5"(0.24MOA) at 600 yards and 5.6"(.56MOA) at 1000 yards
 
Excellent read! Thanks for posting. Very useful info for those of us who may not be shooting off level ground at a target with a horizontal reference line. :) And with a sight height over bore at almost 3" it would only be worse for me.

Speaking of missing threads...does anyone know where the one about anti-cant devices from here went? I thought it was within the last couple of weeks, but I can't seem to find it.
 
Farmer Harv said:
Excellent read! Thanks for posting. Very useful info for those of us who may not be shooting off level ground at a target with a horizontal reference line. :) And with a sight height over bore at almost 3" it would only be worse for me.

Speaking of missing threads...does anyone know where the one about anti-cant devices from here went? I thought it was within the last couple of weeks, but I can't seem to find it.
Click to expand...

http://www.canadiangunnutz.com/forum/showthread.php?t=672764
 
So assuming everything else (including me) working properly*, at 300 I'd expect to miss a standing gopher with two degrees of cant then?

Hmmmm. Good to know. Definitely going to be installing and using a level now.

*Rifle shoots .75 MOA w/windage and elevation dialled in correctly vs average gopher hit zone less than 3" wide x 4" tall
 
Wow. Thanks for taking the time to follow this through and post the results for us to see. May have to look into one of those little levels after all.
 
Next purchase is definitely going to be a scope level. Does anyone have any suggestions as to what mfg make a good one for a 35mm tube?

Thanks,
Justin
 
Farmer Harv said:
So assuming everything else (including me) working properly*, at 300 I'd expect to miss a standing gopher with two degrees of cant then?

Hmmmm. Good to know. Definitely going to be installing and using a level now.

*Rifle shoots .75 MOA w/windage and elevation dialled in correctly vs average gopher hit zone less than 3" wide x 4" tall
Click to expand...

Shooting a standing gopher at 300 yards is a pretty challenging shot.

Canting two degrees (using a .308/155@2900fps) will shift the POI by 0.7". (I used JBM. So your 3/4 MOA group (2.25" diameter) will shift 0.7" left (or right). I would expect most of the shots in your group to still hit.
 
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