I can't pretend to know why someone would make a prefit 300 PRC for a Tikka but I can assure you I would never buy one. You are totally neutering the cartridge buy screwing the barrel onto a Tikka. The cartridge needs 3.7" plus for the bigger and most popular bullets. So I can answer the second part of your question without having built one. You are missing the point of the cartridge if you are building it in a 3.4" action.
Then my next question is, why are 3 major carbon fiber barrel makers making prefit 300 prc for the tikka?
Absolutely!This, its a great 300wsm platform, marginal 300wm, no clue why folks would use it for 300prc. 6.5PRC sure.
Nope. There are longer options than the factory 3.4” but none long enough to fully take advantage of any of the true long action magnums.Maybe someone makes a bottom metal that would accommodate the 300 prc?
Even in a Tikka a 300 PRC handloaded to an OAL to fit the action of 3.4” is going to outperform a 300wsm loaded long and a 300 WM in all bullet weights.
You are not saving any overall weight going with a 300 wsm over a 300 PRC since action lengths are the same in a Tikka.
Not saying I would use a Tikka for it, but Red snake Tactical bottom metal uses and allows AICS LA 3.715” length mags. 3.5”+ COAL without modification in a T3.
I haven't bothered to look up the case dims, if you shove a heavy high BC bullet in far enough to keep to ~3.4" range is the cartridge neck still on the shank of the bullet? (You may very well be, its just something that pops in my head).
The 300 WM case is longer than the 300 PRC. So any bullet that you can load in a Tikka for the WM should be fine in a PRC.
As for the bullet being seated too deep. The PRC case length is 2.580”. The 215 Berger is 1.598. The base to end of bearing surface is .726. That would leave .872 nose length sticking out of the case. Which would put you at 3.452” coal. So too long for a factory Tikka mag but would work with the Redsnake BM.