Ok, I will add a little more...
I'm working on an MX2000, all-in-all pretty much an original gun, no previous work has been done to it as far as I can tell. When I rotate the top lever to the right, The bbls will unlock and the action will open...long before the top lever trip engages. Measuring at the end of the top lever, I can continue moving the top lever another 3/8" before I can get it to lock. Definitely a gun like the original in the first post.
Examining things more closely, the statement I made about lengthening the front of the locking bolt in the previous post, would not help,(but maybe for the TM-1s) The top lever can only move the locking bolt so far...in and out. So that only leads to one cure, recutting the locking notch in the bolt.
Mike,
Maybe you could talk to Dan or Giacomo sometime what the purpose of the long swing of the top lever on the type 4 series of gun when it really isn't necessary. If you ever get a Rem 90-T in your hands, you be surprised as to short the distance is needed to lock the top lever and open the bbls. Now the 90-T does have a patented design that allows this to happen, but with such a short engagement of the locking bolt and the bbl lugs of the MX series of guns, a shorter swing can be had. At least it would be a help to those shooters with short fingers.
As for the TM-1 guns, the bolt engagement is much longer, and I have "experimented" with those on ocassion. When I weld them up for a rebuild, I generally allow the bead to roll over the front edge. A couple of times during the grinding of the new angle, I've forgoten to resquare that front edge. When I then slip the bbl on to check the grind, the top lever will "bottom out" to the right and not allow the bbls to close. So a longer front on the locking bolt would help prevent the premature closing of the top lever in those cases.
Doug Braker