I had a 300 Win Mag built using the Tac21 chassis in 2015.
I too loved the look and feel of it although it didn’t take long to discover its inherent downfalls. First problem I had was with the buttstock lock lever. It would go past the last detent and get stuck behind the detent block. It was a SOB to get it unlocked. Sent the rifle back to the rifle builder and they remedied this by adding a set screw to stop the travel.
The next issues I had were with the magazine stops that are located inside the magwell and held into place loosely but the upper and lower halves of the chassis. They were so loose that they would move around to the point of not allowing the magazine into the chassis at all. I would have to reach inside the magwell and move them back into place to get the magazine in. They finally fell out on their own which fixed that problem.
Next is the buttstock to chassis interface. This was my largest complaint. The version I had is the interference fit where it slides on and uses nylon set screws to take out the slack. No matter how tight I would make this connection, I could easily notice movement. Almost the same type of movement as between the upper and lower of an AR-15. This issue was causing a .2 mil vertical shift in my zero and was where I drew the line and opted for a McMillan A5 adjustable. I have not missed the Tac21 at all.
My last complaint is how the Tac21 makes cleaning and trigger jobs more difficult due to its construction. This is something I didn’t really consider when having it built.
Hopefully others have had better experiences than I have had with this chassis and that mine was just a fluke. I wasted a lot of time and money trying to iron out kinks that I shouldn’t have had in the first place. I certainly have no room for poor quality in my long range budget.
With all this being said, I have had great experiences with other MDT chassis and if I were to do it again today, I would use the ESS.