Ivr only just realised that current generation MBTs (particulaly Leo and M1's) don't appear to have gun travel locks as their predecessors did. Why is this? Surely vibration in travel is just as much of a problem?

Guesswork:
1. Vibration still happens but suspensions are more efficient. The "ride" is a lot smoother today than 30-40 years ago.
Leo 1 (designed late sixties early seventies) still had a travel lock. The Merkava III and 4 still have travel locks.

2. Modern gun stabilisation systems are stronger and more capable of keeping the gun still. Less sensitive to vibrations. The sighting system is not mounted on the gun anymore.

3. Modern sighting systems are less sensitive to vibrations, or rather they can compensate for it. Muzzle reference systems keep track of the muzzle so the problem with misalignment has practically disappeared. The sighting systems keep track of the change in alignment caused by barrel heating (lots of shots fired or heat from sunshine). The problem with dimension changes in barrels due to heat has triggered the use of thermal covers. A "hot" straight line is also VERY conspicuous in a thermal sight. "Look at me! Here I am! Shoot me!"

Experts will probably change some of what I have written above At least add something ....

Edit: I told you so! Stephen W has explained it below
Inside and out .....
/ Robin

Rear end of Leo 1 (Belgian ?)

Image borrowed from Prime Portal

It's inside the turret as opposed to the front or rear deck. There is usually a turret traverse lock. On American tanks that is under the loader's seat. The turret must be locked for the driver to exit on an M1. Have to announce it. The turret has to be locked for the driver to open his hatch on the T-72.

The elevation lock that replaced the old travel lock is on the interior turret roof. Any long ride you engage it to keep the gun from elevating by itself because the gunner forgot to turn the stabilization off or switches it on accidentally reaching for his canteen.

So much easier than sending the loader out all the time to put up the exterior travel lock.

Especially when you can't find the keys to the travel lock.

A quick and easy way also is to put the gun at maximum elevation and turn off turret power. Stab usually requires turret power so as long as everyone keeps their hands off the manual controls you can drive along but maximum safety requires the locks I described above because heavy things can turn by themselves when put at odd angles. Something to do with Higgs boson.

Full disclosure I was an instructor in turret operation for the M60A3 and M1 series tanks. Other tanks may differ but not too much. Only so many ways to operate a turret.

Thank you all very much for that gents.