Thank you all for your time and responses.
@Re-Pete - yes it's definitely that moderator, as @Richiew confirm but I shall also attach photos.
@Richiew - I do my best to clean the moderator but not easy to get in down to the threads, I spray action blaster and Napier rapid degreaser in there, I've tried twisting a rag in too. As far as I can tell they are flat to each other, it feels quite a smooth and solid motion when twisting into place. If we don't find anything definitive, I'll get a gunsmith to check the moderator for gaps.
@Catch-22 -
No excessive smoke without mod, where would the unburnt powder be? I'm using factory ammo, case come fine as far as I can tell (see attached photo of cases from Sunday)
The fit seems smooth and solid, no brake or attachment between. Is this also referred to as a rear bush? Is this something I need?
Moderator has M18x1.0 printed on it, and from what I've found online Tikka T3 are 14x1 for Light Barrels and 18x1 for Varmint.
It is over barrel (see attached photos) I don't know if there is any bushing? It's hard to see in the moderator and it cannot be dismantled, I've attached photos to hopefully help. There is about a 1.5-2mm gap between the barrel exterior and the moderator interior (for the part "sleeving" the barrel).
I do find myself seeing if I can twist the moderator after several shots, but it never moves and takes quite a bit of force to unscrew after use (I have no experience with other moderators, this may be normal)
Thank you very much for all your questions and suggestions, you'll see in some of the photos the embarrassing state of the barrel, I definitely learnt the hard way, and now ensure my guns and equipment are cleaned. As stated the moderator is difficult to inspect in detail, I've heard people mention using ultrasonic cleaning baths. Maybe this would be of use.
If I haven't answered right or provided enough detail please let me know.
Thanks again.