Not only is the fit between the locking bolt and the bbl need to be perfect, but the angles of the two also need to be correct. Most all of the TM-1s and probably the TMXs as well started their life out with a 10 degree or so angle. Ten degrees is the maximum amount of angle you want on most break open gun with such a locking system.
When the gun is fired, the amount of spring pressure helps some to keep the gun closed, but the biggest "component" is the angle. During the shot, the bbl should pinch the locking bolt preventing it from moving. the lesser the angle, the tighter the bolt locks.
Seven degrees begins a locking taper. If the bolt and bbl were at seven degrees, you could not push the top lever open once you closed the gun. I know, I've experimented with that several times. Eight degrees works the best. It's also why shooters talk about the Rem90-T having the locking system "updated" to 8 degrees from ten. The ten degree angle just didn't hold well enough within all the same models.
Somewhere here during the past several years I explained the process we used at Kolar to correct the guns from popping open. With an eight degree bolt and bbl, we cold remove the top lever springs, manually close the gun and shoot it 25 times without the top lever moving. Couldn't do that at ten degrees.
When A Perazzi comes into the shop for a locking bolt rebuild or replacement, I now automatically recut the bbl lugs to 8 degrees, and refit the locking bolt to that. One other thing with the TM-1s that do come into the shop, most have had the locking bolt replace at least once, some many times. And, on those guns, I'm very apt to find that somewhere along the way the bbl lugs have been filed on and that the angle can run from a 5 degree mis-match all the way up to 20 degrees. The real bad ones need to have the bbl lugs welded up, reshape, and the new angle cut.
If you want to try a new spring first...don't forget, there are two springs in that TMX.
Doug
