M81, M162, and XM150 152mm Gun and Missile Launcher

[dy031101]

I took a look at the Wikipedia entries for the M551 Sheridan and the MBT-70 recently......

Despite the guns (M81 for the M551, XM150 for the MBT-70) being described as troublesome, it seems like the troubles have more to do with the ammunitions (being caseless) than the guns themselves- namely ammos being easily cooked off, toxic gas resulting from firing needing to be vented, and, for the shorter-barrelled M81, a violent recoil......

Questions:

• 1. Since muzzle brakes are said to be able to help controlling the recoil, how come nobody seemed to have gotten around fitting one onto the M81 (at least no such efforts have been mentioned)?
• 2. Would anyone be willing to venture a guess as to how much larger the shells would have been if metal cartridge scheme was adopted instead of the caseless scheme?  I guess the problem could mean more to the M551 than it would to the MBT-70 since the latter has an autoloader......
• 3. Does anyone think I've missed other problem with the guns?  Like I said, I've been able to read only problems associated with the ammos...... does it mean that there isn't any real problem strictly with respect to the guns themselves?

[rickshaw]

I think you'll find that if the cartridge cases had been non-combustible they'd actually been a fraction smaller than the combustible, cardboard cases (as metal is stronger and hence can be made thinner).

I also think you'd have found fitting a muzzle-brake to the gun difficult as the fins from the missile would have been likely to foul it.  It also wouldn't have made much difference.  The reality of the Sheridan was that the 152mm gun was simply too large for such a light chassis.  When the Australian Army trialled the vehicle they remarked quite unfavourably on its massive recoil noting that it tended to leap a considerable distance backwards when fired, even with the handbrake applied hard on.   I've often wondered if the vehicle would roll on its side if it was fired athwartships, rather than fore-aft as it seemed to be.

[dy031101]

Are the guns rifled or smoothbore?

[Weaver]

I think you'll find that if the cartridge cases had been non-combustible they'd actually been a fraction smaller than the combustible, cardboard cases (as metal is stronger and hence can be made thinner).

I also think you'd have found fitting a muzzle-brake to the gun difficult as the fins from the missile would have been likely to foul it.  It also wouldn't have made much difference.  The reality of the Sheridan was that the 152mm gun was simply too large for such a light chassis.  When the Australian Army trialled the vehicle they remarked quite unfavourably on its massive recoil noting that it tended to leap a considerable distance backwards when fired, even with the handbrake applied hard on.   I've often wondered if the vehicle would roll on its side if it was fired athwartships, rather than fore-aft as it seemed to be.

I recall reading a post elsewhere by an ex-Sheridan crewman, who said that you could always tell a rookie gunner by the "panda" bruise around his eyes. Knowing about the recoil, the gunner's instinct was to move his face back from the scope before firing. Unfortunately, this was exactly the WRONG thing to do, since the whole vehicle lept backwards, but the inertia of the gunner's head caused him to headbutt the scope violently. The right technique was to press your face hard into the scope, thereby ensuring that head and scope jerked back together.

[jcf]

Are the guns rifled or smoothbore?

Rifled with a keyway to prevent the missile rounds from rotating in the bore.

[jcf]

According to Sheridan by Hunnicutt the XM81 tube design was originally threaded for a muzzle-brake, however the brake was not
developed further and the threads were capped.

The main problem with the caseless rounds was moisture absorption which lead to both crumbling (with the resultant dispersion of propellant in the vehicle) and incomplete combustion, which left shouldering residue in the chamber making the bore evacuation problems worse.

All that said on operations in Vietnam when firing the 'beehive' flechette canister round the gun system was very effective.
With approximately 10,000 darts per round it would strip pretty much grind up anything in its way that wasn't armored.