Range Report Riddle me this (please)

[Phylodog]

Doing some testing this morning for some upcoming training. The goal was to shoot a target from my AR15 at 50 yards which could be used in a classroom to discuss canting the rifle 90* right and 90* left and shooting under/over cover. What I discovered was that canting the rifle on it's left side yielded predictable results, the group was low and left of my POA. Canting the rifle on it's right side had a much smaller effect. Here is the target:

I attempted this twice with identical results. I then had one of my instructors shoot it with my rifle and he had the same result. Another of my instructors shot the same string utilizing an MP5 with an Eotech and his results were what I expected to see from my rifle, canting left put the group low & left, canting the rifle right put the group low right.

My rifle is a 12.5", 7 twist and I was using an Aimpoint T1 and shooting 55gr ball ammo. The only "logical" conclusion I can come to would be the direction of the rifling having an impact but that seems unlikely given the short distance (50 yards).

ETA: After further consideration, I am shooting a Surefire brake which vents left and right. As a right handed shooter when I roll onto my left side the brake is approximately 12" off of the ground. While laying on my right side the brake is moved to within a couple of inches of the ground. Could the close proximity of the brake to the ground be causing interference with the gasses venting equally and causing an unexpected result on target?

Does anyone have a theory as to why I would be seeing this result?

 

[pawprint2]

Good one! Are you going to try to "sand bag" the same weapon, left and right from a bench? If it does the same off the bench- my guess (and only a guess)is the gas ports on the surefire are slightly different as the proximity to the ground or reflective surface would remain the same. Your problem also made me think of firing from a bench with a large block several inches from one side of your gas vents, then the other (l-r) and see if it has an equal effect. I'm looking forward to hearing what you found out-good post.

 

[Phylodog]

I fired both from sand bags and from the ground but when firing from my right side I ended up with the brake close to the bag and blew out the sand bag from the muzzle blast. We just shot it again with a couple different rifles and one of my instructors had the same results, the other was closer to consistent right vs left but the right was still slightly less offset than the left.

I also put my 22lr training upper in and gave it a go. The results were close to exactly what I would expect with the left and right POI being very close to equally low right and low left.

Peculiar....

 

[gstaylorg]

Here is a link to a thread regarding the effect of side to side cant. IIRC, the OP also noticed a difference between the effect of left and right cant on POI, although the difference wasn't nearly as dramatic as yours with the right cant POI being much closer to that of no cant. It's an interesting read if you want to wade through all of it.

http://www.snipershide.com/shooting...7-effects-side-side-cant-field-test-pics.html

 

[Phylodog]

Anyone have any ideas?

 

[XL Mammal]

If you're right-handed, it could be trigger squeeze? If your hand is under the trigger, you may be making contact on the squeeze and slightly raising the rear of the rifle which would cause a lower POI than expected. That's my only guess.

 

[Niles Coyote]

I don't have an answer but will test and report back with an unbraked AR

 

[Niles Coyote]

I tried this but need to do it again with better ammo as my upright and 90 degree right groups blended together and on my 90 degree left group I held the rifle differently on the bench and it was not even close... about 5" low and a little left. Next time I won’t use the bench...

 

[Phylodog]

I appreciate your efforts Niles

 

[bobke]

Could it be a slight difference in how you shoulder the gun to shoot from either side? Or a slight difference in the orientation of your eye to T1? Are you strong right hand/left eye dominant? Couple of possibilities.