If you take the plastic bolt shroud off, and look at the rear of the bolt, you will be able to see down the locking lug raceways on both the left and right side, all the way to the front where the locking lugs engage. The shroud blocks this raceway when the bolt is closed, performing the same function as the shroud on the Winchester 70, Weatherby Mark V, Remington 700, Browning A-Bolt and X-Bolt, Ruger 77, and Mauser 98, and countless others. If you did not read it on my other thread I'll repeat it here. The shroud is there to prevent hot gases traveling down the raceways from striking the shooter in the face. The shroud provides a 90 degree block to those gases, and deflects them at a right angle from the shooters face. This has nothing to do with the firing pin or striker assembly and how it is held in place, or any other function that bolt shrouds may perform on this or any other rifle. In the above rifles it may serve a second function, such as being the end of the striker assembly like the Remington, or being the end of the striker assembly and the location of the safety mechanism like the Winchester or Mauser. But in all cases, including the Tikka, it is also there to block those raceways.
On the Savage 110 series, one of the best designed rifles as far as handling rearward gas flow, there is a large ring of steel, ahead of the bolt handle that acts as a shroud, by blocking the rear of the raceways. The Savage also incorporates a set of baffles behind the locking lugs, that block the raceways directly behind the locking lugs. On controlled round feeding actions, the right raceway is blocked by the extractor, and on the Winchester there is a steel baffle on the left side, opposite the extractor, that is held by a ring around the bolt body blocking the left raceway.
The Tikka does not utilise any baffle system to block the raceways.
Think of it this way, if you were to hook a high pressure water hose to the muzzle, and give it a blast of water down the barrel, where would the water come out. Some may exit throught the firing pin hole at the front of the bolt. Gases going through the bolt body will exit through the vent hole located at the bottom of the bolt (now facing the left hand side of the rifle, in line with the vent hole located at the front left wall of the receiver. Some will also travel the length of the bolt bady, where it will exit thru a relief cut in the bolt handle. On the right side some would come out through the raceway that the locking lug passes thru before it comes into battery. On the left side some will go through the vent hole, and some will continue to move rearward where it will hit the front surface of the shroud. Therefore the shroud is not cosmetic, it is there as a safety feature.
Last edited by dragoon7214; 11/10/09.