Effect of Canting the Rifle on Accuracy

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.

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. 

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.

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!

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.