With a scoped rifle, it’s fairly easy to hold the rifle reasonably “level” using the horizontal reticle line as a horizon reference. Not so easy with iron sights. 

Some simple math shows the lateral error in direction the barrel is pointing becomes quite significant at high rear sight elevations.  For most shooters, this would mean 600 yds and beyond.  

What I thought to be missed wind strength and direction calls at 1000 yds was probably variations in the angle of cant in holding the rifle. 

To give a bit of perspective, if my No. 4 7.62 conversion firing my Long Range load (which requires much less elevation of the rear sight compared to .303 Mk 7 ball) is rotated about the bore axis by 5 degrees, that results in a lateral shift of the bullet point of impact of 3.5 minutes (35 inches at 1000 yards). It is considerably less at 800 yards, about 2.25 MOA (18 inches at 800 yds, half the amount at 1000 yds).  At 600 yds, it’s down to 1.5 MOA (9 inches at 600 yds, or one quarter of what it is at 1000 yds). 

So, how much is 5 degrees? Well, looking at an analog clock, 1 minute movement of the long hand equates to 6 degrees. I’d think looking thru an aperture sight, it would be tough to judge less than a 6 degree cant. 

In any typical 10 shot group, there will be deviations in the angle of cant.  Unless you are using some sort of leveling device, such as a spirit level attached to the rifle, it’s difficult to hold this error to less than 5 degrees (meaning +/- 2.5 deg). 

These errors are enough to move the bullet out of the 10 ring at 600 yards and out of the 7 ring at 1000 yards approaching a complete miss of the target.  If you shoot competition, that’s a big deal. 

This prompted me to try and quantify the deviations in angle of cant in my prone shooting position. Based on my results at the target, I doubted it was as much as +/- 2.5 degrees.  To measure this, I fitted the MantisX training device to the muzzle of the No. 4 and did some dry firing. This records movement of the rifle just prior to and just after trigger release and plots the information in the vertical plane on a target overlay. It also displays the angle of Cant at the moment of trigger release. 

The deviation (max - min) in angle of cant for the 10 rounds of dry fire was 2.8 deg.  I think a 3 degree cant deviation would be reasonable to expect during actual firing, and sometimes probably more. 

A 3 degree deviation results in just over 2 MOA lateral point of impact change at 1000 yds. This seems to explain why I’m getting more than 4 MOA lateral spread on average at 1000 yard 10 shot groups.  It’s not all because of missed wind calls. 

Errors sometimes add, sometimes cancel out.  If my aiming error is 2 MOA, angle of cant is 2 MOA and missed wind shifts is 2 MOA, that could sometimes mean a group that is 6 MOA wide, The diameter of the 7 ring on the Long Range Target.  But, sometimes the errors cancel, and you get what I had last time with 4 consecutive shots within less than 1 MOA. 

If anyone has made it this far, you’re a shooter for sure! 

MantisX installed on No. 4 DCRA below: 

MantisX display showing muzzle movement: 

   Blue line -  during the hold just prior to striker release

   Yellow line -  movement during striker release

   Red line - after striker release. 

Angle of cant shows in the upper right box, it is 4.4 degrees.  The zig-zag line shape I believe is due to my pulse. 

This is a useful training aid to show you how much rifle movement occurs at the time of striker release. This image is zoomed way in to the inner “X” ring on the target overlay. Movement is much more in the standing position. 

Just found this snippet in the 2004 Bisley Bible Geoff; I seem to recall such items were banned in Target Rifle in the past but not Match Rifle where anything (scopes, Gallien sights etc.) goes. 

I ran another dry fire test, this time breaking position for each shot (taking rifle down off the shoulder, working action, then back up on the shoulder and “fire”).  This time I really concentrated on holding the rifle as level as possible based on the vertical front ring supporting strips.  That got the canting angle deviation (max - min) down to 1.6 degrees (1.12 MOA lateral spread at 1000 yds). That’s much better.  

I never really thought about this or paying particular attention to trying to hold the rifle consistently level.  Now curious to see if I get any improvement next time I shoot the rifle at 800 and 1000 yds.

Me neither Geoff; I'm at 600 & 900 at Bisley on the 14th; I hadn't planned to shoot my No.4 but you've roused my curiosity! 

The only time I pay any particular attention in shot to shot angle of cant is at the 600 yd prone slow fire stage with the AR Service Rifle looking thru the scope. I also check my initial position during the 200 yard sitting rapid fire stage as I deliberately cant the rifle about 15 degrees to the right so I could get good head position on the stock and eye alignment to see thru the scope. I “index” the angle of cant by looking at the horizontal reticle line position on the two adjacent targets such that it is at the top edge on the target to the left and bottom edge on the target to the right.  This amount of cant causes a significant shift of the bullet POI at 200 yards and the sight elevation and windage settings adjusted accordingly.

 It’s all about shot to shot consistency. 

Mick, I actually think it was you that got me thinking of this some months back! But I put it in the back of my mind until I saw the results of last Mondays 1000 yard shoot. 

I have a tendency to cant to the right. Always the right no matter what rifle! Its just something i instinctively do, just not a good instinct! With the FAL I used the magazine as a guide! if it was not just touching the inside of the left forearm I was canting right!

For that reason & the fact there's precious little "Square, Vertical, or Horizontal" places on a No4 I found & added this little bubble level to the scope mounting rail! It was just a few bucks on E-Bay.

Its reasonably well sheltered from knocks or anything & mounts to the dovetails in the mount so it IS square! You can see it simply  by opening the left eye & glancing slightly downwards.

I originally intended it to be a temporary "training aid" to break the habit, but its become a fixture since I don't compete formally any more

My copy of the textbook of small arms p64 has a bit on the effect of canting the rifle during the act of aiming.

It would be interesting based on the determination of two accomplished shooters and with use of some of the technology as described above to see what else can be learned by what they actually  experience.

Because I cant shoot well enough to any great distance I personally cannot say.

Or really I should probably say that Im not dedicated or squared away enough to make an accurate distinction based on my own application of marksmanship principles.

Anyway, I have often read to where others express (even argue) that there is no effect of canting the rifle to which I don't believe based on my own humble experience.

Hey, nice to see you posting.

Ask those same shooters if they square their scope reticle or just get it close & see what they say!

It has been proven experimentally as well.

 Here, I’ve attempted to quantify the amount of shot to shot variance in the cant angle by use of the MantisX training aid.  I’ve read in a few places that the best marksman can hold to an angle of 3 degrees or less. That seems to be true based on my own measurements.

Canting does also affect elevation POI, but this is not significant for relatively small angles (6 degrees and less) out to 1000 yards, here is an example:

For a 40 MOA rear sight elevation required for 1000 yards (typical .308 with a 168-175 grain high BC long range bullet at a MV of 2600 to 2650 fps): 

  5 deg of cant gives 0.15 MOA reduced elevation POI and 3.5 MOA lateral POI deviation. 

10 deg of cant gives 0.61 MOA reduced elevation POI and 6.95 MOA lateral POI deviation.

10 degrees is very excessive and would be obvious to any level of shooter I would think. For a serious Service Rifle competitor, anything over 1 MOA deviation is worth trying to correct or minimize.  Guys shooting long range PRS, Bench Rest or F-Class definitely worry about this and do what they can to minimize it.

If you’re shooting at 100 yards, you can ignore this entirely, but you would see an impact if you shoot gangster style laying the rifle over on its side like in the movies!

If you read the installation instructions for most of the old Target sights they are big on "squaring them" which is a (kind of) reverse cant!

Literally shims, heating & bending mount adopters a so on are all mentioned as essential.

My "Central" sight for the SMLE actually has a neat double screw coaxial adjustment built in for doing this without heating, bashing or bending the plate.

In setting up the scope on the T, great care was taken by H&H to culminate and true the scope to the individual rifle.  I can’t detect any change in lateral POI in my T between 100 and 600 yard scope settings as long as I hold the horizontal graticule line in the scope level. 

im putting one on my kimber bench rest rifle as well , 

The mantlet on Century range at Bisley is far from straight in some places and I have to rely on a bubble which makes the scope cross hairs look crooked.

It did occur to me and I haven't had a chance to experiment yet; shooting at a tin hat target with a standard Enfield foresight post would I believe make you correct the majority of cant by instinct?? 

Thoughts?  

With a scoped rifle, the natural tendency is to hold the horizontal reticule line parallel to the horizon, or some other reference. As far as I know, the target line at Talladega is level, so I align the horizontal graticule on the No. 32 scope with the line of target frames. 

But, shooting with a front and rear aperture sight, there is not much of a line on the sights to hold a horizontal reference to. Just those little strips of metal in the foresight insert.  

What’s absolutely critical, I believe, is holding a constant angle of cant thru an entire string at long range (800 yards and up).  Otherwise, you will see wide lateral spreads that you may think are due to poor wind calls.