@ 08:41 am (GMT)
Nathan FosterOK, here we go. Expert advice, otherwise known as long distance guess work.
1. There is a high possibility that the brake is reducing recoil to the shoulder but then creating a concussion shock wave which creates a more subtle yet insidious problem. This problem can be worse than issues caused by felt recoil. Not a great many people understand this so don't bother googling it.
2. Brake is removed to isolate rifle on its own but technique is not optimal to control rifle. If so, this should be seen as a core issue. Fix this issue via technique, not via alterations to the rifle during formative learning. Alter the rifle following personal mastery. A bit like saying- well I know the rifle has potential, groups are looking good, but now the testing is done, I can see its still too light for me to use with a fast heart rate on a windy ridge so now I will set about obtaining a fatter stock etc. This order of steps is quite important for long term success in this field because you have isolated the most important variable, yourself.
1. Brake is is not venting correctly. Remove brake to isolate this variable.
2. Loads are not concentric, yaw increased with additional velocity / spin. Study bullet run out (Sinclair gauge) to assess this.
3. Action screws over torqued (see Accurizing book / Tikka set up video).
4. (now or later) Muzzle gradually swells at threads. Too narrow for this power level over time.
5. Carbon caking at muzzle section makes already slippery bore too slippery. Also possible carbon caking further back towards chamber depending on brake design. Look for obvious signs of heavy carbon during extraction, smoke coming from chamber.
Velocity wise, your rifle is producing the same speed as Hornady SF ammo. The Tikka rifles often shoot well with this load. But again, other variables have to be isolated.