Why might my rifle have lost zero

[stan_wa]

All right, well like many of you. I think it’s really important for your rifle to be zeroed well and to stay zeroed.
I sightes my rifle in and I established a zero using 10 shots and the center was right where I expected it to be using the group analysis app I was splitting the difference between .1 mill and couldn’t get the center of the group any closer than it was.
So I take the rifle hunting shoot some rocks while I’m out there and seems to do fine. Come home make a trip out to the range two weeks later after no significant abuse and just ridding around highway in the case I’m .4 mil low .2 mil right @ 100 yards
Both initial and follow up zero where shot with the same bipod and rear bag.

Environmentals did change 500 ft 50 deg vs 1800 ft 75 degree

Set up
Rifle : havak element with integrated pic rail
Scope :trijicon ten mile ffp 3-18
Rings : seekins precision rings
Install : seekins recommended torque value with blue lock tite in actions screw, ring to pic rail screws and scope clamp screws .

I’m stumped only thing I can think is maybe I need to center the rings on the tube more , rear ring is .150” away from zoom
Ring

 

[ResearchinStuff]

Check your rings for cracks.

 

[Mortar]

Could be the power sensitivity to temp, although that is not a drastic change in temps. Also different lot numbers in ammo can be a factor. Keep detailed notes on your changes after checking your torques and rings. Ammo for me has been the most common offender. I typically shoot factory loaded ammo.

 

[Macintosh]

Witness marks on the scope tube/rings to see if the scope slipped?

Do the groups look different, ie was one round and other strung horizontally, or something like that, in a way that might indicate it was a recoil/position difference?

I havent seen environmentals shift a 100 yard zero measurably, but I would not expect a 1300’ elevation change to do that, even in combination with a temp change.

 

[Wrench]

Is this at 100yds or 1000yds?

 

[DangerRanger]

What’s the recommended torque value on the rings?

 

[stan_wa]

Could be the power sensitivity to temp, although that is not a drastic change in temps. Also different lot numbers in ammo can be a factor. Keep detailed notes on your changes after checking your torques and rings. Ammo for me has been the most common offender. I typically shoot factory loaded ammo.

These are all hand loads using Rumbo so it’s pretty temperature insensitive at least about as good as you can get, and I have not been tracking the lots on the powder itself

 

[stan_wa]

What’s the recommended torque value on the rings?

100 yards
But I was pretty low at 700 As well , I actually started at 700 was low and that made me
Check zero

 

[stan_wa]

What’s the recommended torque value on the rings?

Ring clamp is 50-55 inch lbs. Ring cap is 20 inch lbs.

 

[Lawnboi]

Is your rifle broken in? I don’t expect a barrel to stabilize until it has 100-200 rounds through it

 

[TaperPin]

If you like to load the bipod, it’s a good idea to shoot groups with different amount of load - the more pressure the more groups will go low. Even without a bipod, more shoulder pressure will shoot lower.

Also, what the bipod is sitting on can change vertical zero. Harris bipods are famous for having issues on hard surfaces as they try to hopp during recoil.

What your groups are doing will make more sense with more context - some of us keep shooting logs so every zero change is recorded - I always note what kind of rest and if it’s a bipod, what surface it’s resting on. Moving zero back and forth might be scope, mounting, bedding, bipod, barrel touching stock, plastic stock warping in sun, inconsistent ignition. Ranges without wind flags, or ignoring wind, contributes to a moving zero.

 

[slowelk]

What about action screw torque?

 

[Mortar]

Just came across this video don’t by MDT on YouTube. He loosens muzzle brake, front then rear action screw and scope to show the shifts one thing can cause. Immediately thought of this post. Good watch for refrence.

 

[stan_wa]

Is your rifle broken in? I don’t expect a barrel to stabilize until it has 100-200 rounds through it

600-700 rounds on it no cleaning between trips

 

[stan_wa]

What about action screw torque?

I contacted Seekins and the spec for the action is 55in/lbs. so that’s what I used and I degreased bolts abs used blue lockite

If you like to load the bipod, it’s a good idea to shoot groups with different amount of load - the more pressure the more groups will go low. Even without a bipod, more shoulder pressure will shoot lower.

Also, what the bipod is sitting on can change vertical zero. Harris bipods are famous for having issues on hard surfaces as they try to hopp during recoil.

What your groups are doing will make more sense with more context - some of us keep shooting logs so every zero change is recorded - I always note what kind of rest and if it’s a bipod, what surface it’s resting on. Moving zero back and forth might be scope, mounting, bedding, bipod, barrel touching stock, plastic stock warping in sun, inconsistent ignition. Ranges without wind flags, or ignoring wind, contributes to a moving zero.

I have also experienced this, bipod load, hand pressure , ground surface and face pressure all make an affect. So shooting my 2nd zero check I tried gravel and concrete, fully loaded and no bipod load. I could see these changes create a larger than normal group as I was purposely not being consistent , but the center was way off

So my process was initial sight in


Adjust to get zeroed then shot this in 4/28 the scope tracked as expected and basically I have 13 shots to Inform this rifles zero



Then went hunting for a 5 days , shot rocks had good hits, came home went to the range after some shooting and missing shot a zero check that produced this.

And yes Memorial Day zero check produced a “worse group “ but keep in mind I was switching positions and intentionally adding different bipod load and face pressure to see if I could get the shot “back to zero”



I’ll check muzzle break for tightness , rings for cracks and marks in The scope indicating a slip when I get home

 

[Wrench]

"Bipod load and face pressure" that's enough to change the group.

I am not a great shot from a bipod but shoot very well from a backpack set up to mimic bags. I have to assume it's because I can be most consistent with recoil when supported by the bag.

 

[stan_wa]

"Bipod load and face pressure" that's enough to change the group.

I am not a great shot from a bipod but shoot very well from a backpack set up to mimic bags. I have to assume it's because I can be most consistent with recoil when supported by the bag.

Im fairly certain that was not the cause I was testing extream variances in theses inputs and could see only a small shift and it was still way off center

 

[TaperPin]

It will be interesting to see if the zero continues to move up and down. My older brother had a rifle that slowly increased group size over a ten year period until I bought it from him - over two years I couldn’t get it to shoot better and sold it to a friend. Groups clumped in two parts, one higher, one lower. Turned out an internal lens was loose - had my brother or I swapped scopes, the gun shot so well we wouldn’t have sold it. Lol

 

[jimh406]

Try a different scope/rings. It would be pretty simple troubleshooting.

 

[stan_wa]

Try a different scope/rings. It would be pretty simple troubleshooting.

The hard thing about this is I’ve gone on probably four range trips with the scope and proven that it did hold zero in the same set up and then suddenly it didn’t which is concerning so I can’t directly test it because the response can be erratic