Rifle Scopes Zero Issues (LT-111 / T5Xi)

[spear76]

Looking for some help,

I have a T5Xi 5-25 secured in a LaRue LT-111 mount on a 6.5 RPR, shooting Federal Non-Typical 140gr. I have checked my zero on 3 different range trips at this point (Not consecutively) and the zero seems to have moved on me. I'm using 25 in/lbs of torque on the rings per LaRue's response via e-mail for 22-25. I am wondering if I am not torqueing the rings to the tube tight enough and should go a little tighter or if perhaps something else is causing the issue.

The following are my environmentals and adjustments needed to obtain zero on the range trips. POI is in inches.

Original zero: 01/15/19
Alt: 674'
Angle: 0*
Temp: 34*
Dist: 100yd

Second zero: 01/28/19
Alt: 289'
Angle: 0*
Temp: 27*
Dist: 98yd
This club didn't have enough room for me to move the target back while shooting from prone.
POI: 0.4Left, 0.43Low

Third zero: 02/14/19
Alt: 674'
Angle: +4*
Temp: 37*
Dist: 100yd
POI: 0.71Left, 1.70High

Could I need a higher torque? If so, what should my max be without harming the scope and in what increments should I start going higher? Is it because of the ammunition I'm using? Or is it the slight change in environmental?

I'm completely puzzled here and could really use the help.

 

[HellsCanyonArmory]

Does the rifle group consistently with each range session? Are you verifying all the parallax is removed from the sight picture? Parallax issues cause 90% of the issues with shooting small groups at 100 yards. Most the time because shooters just spin the knob to 100 and start pulling triggers.

Did you change shooting rests either time? My zero will absolutely change from a bench and bipod/bag to probe on concrete to prone on gravel or dirt.

If the groups aren’t stringing vertically, then most likely your mounts are fine and something else is to blame.

 

[spear76]

The rests have kind of changed, for everything I'm using an Atlas bipod. But each time was a little different, as far as, surface the bipod is on. Initial was rubber feet on a bench, second was spike feet on stone and third was spike feet on ice.

The groups are stringing vertically. 0.43 inch on the second zero and 1.7 inch on the zero today.

I'm thinking I may use a micrometer to measure and record the distance from a specific spot on the scope to a specific spot on the mount. That way I can tell if it's sliding fore or aft. Do you think that'll be a sufficient way to tell if it's sliding?

 

[_Windrider_]

Couple things.

1. Make sure the rings are pushed forward against the recoil lug on the rail.
2. Make sure the rail on the action is tight, mine was loose when I first got my RPR
3. Check torque on ring lugs that hold rings on rail, usually 65 inch lbs
4. Could be ammo but I doubt it

 

[HellsCanyonArmory]

The rests have kind of changed, for everything I'm using an Atlas bipod. But each time was a little different, as far as, surface the bipod is on. Initial was rubber feet on a bench, second was spike feet on stone and third was spike feet on ice.

The groups are stringing vertically. 0.43 inch on the second zero and 1.7 inch on the zero today.

I'm thinking I may use a micrometer to measure and record the distance from a specific spot on the scope to a specific spot on the mount. That way I can tell if it's sliding fore or aft. Do you think that'll be a sufficient way to tell if it's sliding?

I’ve measured from front of ring face to front of rail before with a set of rings that weren’t staying seated on the pic rail and noticed them changing .005” from mounting (seated forward in the slot) to returning from the range.

I would attempt to check POI shift from a few different shooting positions during the same range session. Also make sure and tune the parallax out every time. I’ve had scopes that would eliminate vertical parallax but wouldn’t fully eliminate horizontal parallax and groups always strung horizontally because of it.

 

[spear76]

Thanks for the tips guys.

Before my next range session I'll take the scope off and re-torque everything down, then remount and take a few measurements. At the range I'll confirm a zero then experiment with shooting from bench, dirt and concrete to see if I get any noticeable stringing.

 

[ShtrRdy]

Are your groups small but in different locations?
The POI change you listed - is that inches or mils?

 

[lancetkenyon]

I have found different POI for different shooting positions. From a bench to prone is usually about .5" L/R and .5" U/D. Recoil management is the culprit.

Which is why I could care less WHERE my POI when shooting from a bench. All of my scopes are zeroed for prone. I figure if I am shooting offhand, it is a close shot, where .5-1" is not going to matter anyway. Seated, the POI difference is much less. And prone would be for any long shot, which is where I need my zero to be spot on.

Have you been dialing between range sessions?
Have you performed a tracking/Return to Zero test?
Your look angle could make a difference at longer distances, but I doubt 4* would make much at 100 yards.
Have you adjusted parallax?
Wind?
Shooting position.
Cheek weld.

 

[spear76]

@ShtrRdy my groups are all under .4 inches and yes, my listed POI changes are listed in inches.

@lancetkenyon I have been dialing during range sessions to shoot at distance. I just received a few test targets from Box to Bench to test the returns. But so far, I haven't had an issue during a range session to return correctly. Stock and parallax are all set and haven't changed since I set up the rifle.

At this point I think my best approach is going to be recheck the torque on the entire rifle, confirm a zero and shoot from different prone surfaces on my next outing. Then do the tracking test as well.

 

[_Windrider_]

@ShtrRdy my groups are all under .4 inches and yes, my listed POI changes are listed in inches.

@lancetkenyon I have been dialing during range sessions to shoot at distance. I just received a few test targets from Box to Bench to test the returns. But so far, I haven't had an issue during a range session to return correctly. Stock and parallax are all set and haven't changed since I set up the rifle.

At this point I think my best approach is going to be recheck the torque on the entire rifle, confirm a zero and shoot from different prone surfaces on my next outing. Then do the tracking test as well.

One other thing to consider, the RPR is notorious for the barrel nut to be torqued way beyond what is necessary. Could be some stress in the barrel. My 2 cents, tear the rifle down and put it back together.

 

[spear76]

Didn't even think to mess with the barrel nut. Thanks!

 

[spear76]

Forgot to update this thread.

After a little experimentation I decided to remove the barrel nut and re-torque. Problem solved!

Thanks to @TacticalDillhole for his .2 cents!