Cause of split groups?

I'm trying to figure out what the cause of these split groups could be, they are consistent across other groups as well to the point if you overlay other targets you see straight through both of them. T3X 7mmRM, DPT supressor with a Steiner Predator 8 3-24x50 on Talley rings. Definitely not parallax as I made sure to set it exactly right, and I check the supressors tight before every shot. Pretty consistent across two different factory ammo and a handload ladder. And it's not the last two shots or just when the barrels hot etc, the throws on this group were 2 & 4.

Looking online people have suggested the scope mounting, that got me thinking to when I purchased the rifle I saw a dremel being used during the mounting process, I took the rings off a scope I had previously purchased from them and from my untrained eye it seems fine, the finish is most definitely not a dremel finish and feels very smooth, so I'm guessing this is a non issue but I've included a picture just in case.

I've had someone else shoot the rifle to rule out the me factor but they weren't the greatest shot so wasn't much help, but I'd like to think I'd know if I was throwing it that much. Gonna have someone else shoot it in a couple days but in the meantime any ideas as to what could be the cause of this?

double group = bedding
USUALLY
what happens is the barrel /action is sitting in stock,here for couple of shots,then it moves to its "other happy place" and shots go to other place
oversimplified explanation for clarity.
my old 308 used to clunk at random times..drove me nuts till one day held barrel and stock and realised could move them about 2mm back n forward...it had absolutely zero bedding.

It is really like something is jumping around - your groups are good so likely not you- but try a different shooter and one who can shoot - its like something is moving -or as Mickey Duck is saying could be bedding -the barrel is jumping from side to side possibly - but those mounts what did they do and why with a dremel - looking at the job it does not look precision at all if one was trying to true a mount - look at the bedding if its okay well then try a different scope in those mounts for a start - if that holds correct consistent zero then likely the windage adjustment in the Steiner scope -still does it then try different mounts -- but if all your screws are correct torque then the windage adjustment could be the problem - sorry cant be more help - good luck you will just have to work thru a process of elimination - I fixed tractors for awhile and when I got to one that would not start the first thing I did was look in the diesel tank and with a torch did not even trust the gauge - one step at a time treat it as a process and start from real basics

7mm mag...hmmmm do you fire three shots,then load another two in rifle and then shoot them??? So possible you have different position??nah your two n four rules that out....but that suggests one three n five also form group so definitely suggests something moves too n fro consistently with each shot it switches position.....

are the bases tight , had a mossburg that moa 5shots then next 5 was 4ins right and 4inches low turns out factory base was loose and scope flopped to one side if I held slightly differently .

try this - clamp that rifle in a vice - yes obviously pad the vice well- leather is best - a wood work vice better than an engineers vice - then try and move barrel in the stock - I have seen an early Tikka 690 .270 that moved several millimetre clunking side to side - - what gave the show away with that rifle was when one looked down the barrel at the gap between barrel and stock it was uneven -the barrel was over slightly in stock - undo screws move and tighten again and hello gap is the other way - a bedding job from a gunsmith solved it and then that .270 was a tack driver - but I would be avoiding the shop that took to that mount with a dremel - a true dolly designed to lap mounts and a cutting compound is what I understand is required

The rifle is to precise for just a random flopping around - Id out my money with Micky Duck's and blame bedding, or the absence of it.

Most likely something is shifting from side to side, to make that pattern so repeatable. Previous answers have pretty well covered it.

Bedding/action screws are a solid possibility, can hold the stock and wiggle the barrel to look for obvious play, but I would start by taking off your scope (leaving it in the rings would be fine for this), then check the bases are tight if your tikka uses them. The crossbolt screws on the rings would be my next most likely culprit.

Scope internals are a possibility, but well down the list I feel. Give the ocular bell and focus ring a wiggle just in case there’s anything obvious.

Tikka have the recoil lug in the stock, is it in correctly with the action, as I’ve seen them put back incorrectly, if it’s not the barrel is usually sitting up out of the barrel channel

I had a situation with results like that.
The front sling stud was protuding through the stock and touching the barrel. The barrel would hop from one side to the other causing two groups.
Put a spacer under the stud and it fixed it.

I sorted one for a fella the other day doing same thing in 300 win mag
Light weight strata first thing I would look out would be scope mounting and bedding
Use some araldite super strength or Devcon clear epoxy
On the side of the base screw thread with a tooth pick
Don’t put on the bottom of the screw gets into the action
And action threads and is a pain to remove
And on bottom of the base/rail clean up with some acetone or brake
Clean on a rag after it been torqued down
Heavier scopes and light rifles a lot of times loctite does not hold the best
After a while
Even worse when it comes to cerakote
Would try this first as cheap to check

Next be bedding the action like the rest have said with a 1.5” long pad under the barrel
With the rest free floated

Greetings,
That scope ring looks suspect to me. It looks as if it has been lapped and the top part replaced because it is now too loose. At least the two parts of the ring are mis matched. What happened to the original rings the rifle came with?
GPM.

Double grouping. Did you know where your shots fell ie no1 in the bull, no 2 to the right, no 3 back in the bull etc that's a definite diagnosis of bedding failure.

Agree it’s most likely an action/bedding or recoil lug problem. Have you checked the action screws for torque ? Get hold of a torque wrench and check what pressure they’ve been tightened to. If they are loose that could be the problem. Be careful not to over tighten as this can bugger up the free floating recoil lug set up which is critical to the design of T3s. From memory torque should 30 or 35 in/lbs max for Tikka factory stocks. I’m assuming it’s a factory Tikka stock ? Is it ? If it’s an after market stock with ali bedding block then that can present other issues.
Take the action out of the stock and carefully inspect the stock internals where the action sits for signs of rubbing and also check the bottom of action looking for rub marks. This will confirm that you’ve got a bedding or seating issue. When you’ve got it apart check there’s no shite to grit trapped anywhere, especially in recoil lug area and recess.

Front action screw a tad too long and bottoming out?
I had a new Remington Mohawk .308 where the screw protruded up and was jamming against the bolt lug.
Also a CZ457 where the front screw was too long and bottomed out in the action.

well lots of great advice maybe do a list of key points of here and go thru one by one - starting with the obvious - a magnifying glass would be handy - test for movement first -take action and barrel out and have a really good look - and as others have said that mount looks damn dodgy - but some great points on here to look for - even basics like does the barrel sit square in the stock or is it off to one side - the awnser could be bloody obvious its just one has missed it - this is a slightly weird one and I say that because its not a known problem with new tikkas - they are computor made and normally all come of the line shooting - but mistakes happen - saw a Remington a while ago and the bloody screw holes for scope mounts were out of line to action and barrel and a chinese .22 where the bore was of center to the barrel

Moving your position slightly between split groups.Hands,butt on sholder,feet.Moving body position slightly.

Group issue is well covered

How's the scope?

Thanks for the all the input fellas very helpful, I've made a bit of a list easiest and cheapest first and started with pulling the stock off - first thing I noticed was the action screws were snug but not as tight as I'd think it should be, second thing was the thread insert for the front stud was 3/4 of the way out the hole, it looks like it was never inserted properly from factory, I'm thinking that could have caused some shift in bipod positioning. Cleaned and reinstalled the thread insert, and torqued the action screws. I noticed the positioning of the rear screw is now centred whereas before I took it apart it was hard to one side. Hoping one of those two fixes it if not I'll move down the list.

Scope is good although I can't comment on it's performance beyond the range yet, got one animal with it but in hardly testing conditions. Waiting to get this rifle sorted before I head out to glass some slips. It's a difficult scope to find reviews for, one of the only in-depth reviews I could find was in a magazine, I'll PM it to you

good man- I really expected mechanical not you - if you took anything away from all the info then slowly eliminate all possible - and carefully work thru them - I dont doubt this is actually simple as Tikkas normally shoot -