Rifle Scopes Scope zeroing questions

[Braindoc]

On a lark I decided to put an Athlon Argos BTR 8x34x50 FFP mil scope with Vortex Viper medium rings (which was on my Ruger 10-22) on my Ruger American 7.62x39 rifle because I got tired of using a Nikon P300 scope with its BDC type estimations. So the Ruger has its stock 0 elevation Piccatinny base. The mounting was easy but when I went to zero it I found that it was shooting quite high even with the scope elevation all bottomed out, I had to use the mil markings above the crosshair. At 100 yards POA=POI at the +4 mil hatch, 200 meters at +3.5 mils and 300 meters at the +2.0 mil and my calculations using the ballistic app estimates clicking up 2.4 mils more to hit 500 meters.

Any suggestions on how to approach this? I am contemplating switching the Vortex scope rings fore and aft first. Maybe the front ring is taller than the rear? I don't recall the Athlon Argos having a scope stop that I missed? Maybe the scope base is off or the barrel is a little tilted up?

Thanks,
Ray

 

[dirthead1]

Have you checked to see if you are hitting the zero stop? You should have no problem zeroing, especially with a zero moa base.

 

[Braindoc]

I took the turret cap off, no washers or shims to act as a zero stop. From the bottomed out zero I have 15 mils of rotation to reach the top. Maybe I have to ask Athlon about the specs of the scope.

 

[dirthead1]

Do you have the owners manual? I would check the zeroing procedure. You can probably download it from their website as well. You are most likely just bumping up against the zero stop. Maybe try loosening the turret cap screws and turning the turret up about 3 mils, then retighten the cap screws. That should reset the zero stop down enough to zero.

 

[Dthomas3523]

That optic is spec’d for 13 mil total elevation. Theoretically with a zero moa base you should be around 6.5 mil travel in either direction when zero’d.

Something is wrong if you have it adjust all the way to the bottom of the erector and still cannot zero.

 

[Braindoc]

It is strange indeed. The Athlon was used on my Ruger 10-22 with a 20 MOA base before and was predictable with a ballistic app to hit at 200 and 300 meters. On the Ruger the scope was also close bottomed out but able to zero at 25 and 50 meters. Also of note was when I transferred the scope from the 10-22 to the American I only had to adjust a few clicks to the left and the POI was in midline. So what to look at next? Rings, base or barrel?

 

[Braindoc]

I finally took the setup apart and remounted the scope. I examined the Pic rail and notice that that at the rail wasn't entirely flat on top. There seemed to be a slight dip towards the very front end and so I remounted my front ring a notch back and the rear ring a notch from the end. Remount the scope as usual.

Back at the range I was able to zero the rifle with the 100 yard zero as expected near the middle of the elevation range. Windage zeroing was almost the same.

It looks like that Piccatinny rail defect was like a >20 MOA effect on the scope. Hence the difficulty zeroing.

Thanks to all for helping out!