The Tromboncino Model 28
By Anthony Dee

The Tromboncino (Small Blunderbuss) is the Italian Military term for rifle-grenade devices. The Model 28 was developed in 1928 and was in use only until 1934. It was Italy’s attempt to adopt a grenade launcher to a rifle; similar to the current model 203 grenade launcher we see attached to the M16. This concept was very advanced for 1928. The operational requirement was for a light, easy to use weapon to be used to “stun” the defenders of an enemy trench, forcing them to keep their heads down. The grenade that was designed for this launcher was a so called “offensive grenade” as it produced very little shrapnel. It was a forerunner to our present day “Flash- Bang” type grenades. This reduced shrapnel effect was required so the weapon could be used up to the last moment of the assault, without endangering friendly troops advancing in the open. It was planned to issue the Tromboncino to five men in each rifle squad (platoon).

To accomplish this, a common M91/28 Truppe Speciale Carbine was fitted with a complete auxiliary receiver attached to the right side of the rifle. This receiver was similar to the Carcano with the addition of a smooth bore grenade tube with a diameter of 38.5mm (1-1/2 in.). When the grenade launcher was to be used, the bolt would be removed from the rifle and inserted into the grenade launcher. A single round of standard 6.5x52mm Carcano ammunition was loaded into the breech. This round fit into a special combustion chamber that was closed at the front by a threaded plug. This chamber was heavily manufactured and was fitted with 4 holes to relieve the pressure. A grenade was then loaded into the muzzle of the tube and was placed against the threaded plug. When fired, the bullet would leave the case but only travel a short distance. The gasses would be vented off through the 4 holes and into the rear of the grenade tube and thus launch the grenade.

The bolt then could be opened and the expended bullet would just fall out of the Combustion Chamber. The bolt could then be returned to the carbine and be used for conventional firing.

This concept seems bizarre but in reality is quite unique. No special ammunition is required and the grenade launcher was fired using the same trigger as the rifle through a simple linkage system. The sights on the carbine were modified with the addition of a bead front sight attached to the barrel and protruded through the left side of the hand guard. The existing rear sight was modified with an extended, offset leaf. Elevation numbers were marked on the side of the rear sight base to correspond with the moveable leaf. The range was marked from 100 meters to a maximum of 200 meters.

Two grenades were used in this system and information regarding them has been very difficult to obtain. The first type is an inert practice grenade. This grenade was constructed out of a wooden dowel that was covered in sheet metal. It was quite short and was only 72mm (2.83 in.) long.

The other grenade was the live round and was designated the S.R.2. This was an impact-type round with an internal fragmentation coil. The S.R.2 Bomb with Stabilizer was to be used with the shortened stem Model 28 Tromboncino only.

The stem refers to the threaded plug in the combustion chamber. The short practice grenade used the “Long Stem” plug and the live grenade used the “Short Stem” plug. This stem determined the depth of the grenade when placed in the tube. This information was recently verified after two different examples were examined.

The grenade was held in the tube by means of a spring loaded plunger that can be seen as a large knurled knob on the underside of the tube close to the muzzle. This allowed the rifle to be carried with a grenade in the tube ready to launch.

Very few of these carbines were imported into the United States. Research has shown that only 14 serial numbers have been recorded from a shipment that entered the country between 1959 and 1960. The manufacturers of the Model 28 Tromboncino launchers that are known are the Terni Arsenal, MBT (Metallurgica Bresciana) and Lorenzctti, Brescia. The launchers were placed on carbines of the other makers of the Model 91/ 28 T.S., such as Beretta and FNABrescia. By 1934, the Model 28 was discontinued. Being in service for such a short time verifies the system’s drawbacks and weaknesses. The tube, receiver and combustion chamber wereall made of heavy gauge steel. This increased the weight dramatically and it was very difficult and expensive to manufacture. The grenade, being small in size and payload, had limited use. The maximumlaunch distance was approximately 200 meters and it was reported to have a very small blast radius.

The Model 38 Cavalry Carbine and the Model 38 T.S. (Truppe Speciale) were introduced in 1938 along with a new caliber the 7.35X53mm Carcano. The Tromboncino Model 28 was already discontinued; however there were large stockpiles of parts and stocks that were already manufactured. The Tromboncino Model 28 was designated to be implemented onto these carbines. This never came to pass but the parts were recycled onto these models.

There are several examples of Model 38 stocks that have been cut out and inletted for the Tromboncino. These inlays were filled in a very elaborate manner and the stocks reissued. The barrels on these carbines also show a notch cut out in the top to clear a cross bolt that attaches the Tromboncino to the carbine. These modifications are mostly on Model 38 Cavalry Carbines manufactured by Gardone with serial numbers from “A” through G1216. The Model 38 T.S. in 7.35x53mm is the rarest of all the Carcano models in its standard form to find. Very few were made and none have ever been seen or even heard of that has been fitted with a Model 28 Tromboncino.

The Italian arms makers were very well known to recycle, reline, and retrofit arms to meet the needs of the Government. Very few parts were disposed of if they could be used in any fashion. Handguards and barrels cut for the Tromboncino are found on several other models of Carcano’s. A far cry of what we see today.

The Tromboncino Model 28 was an innovative design unlike any other seen in this period of weapons development. Unfortunately, the concept proved unworkable but remains a unique piece of armament history. It was replaced by the Model 35 Brixia Assault Mortar. This mortar also used a reduced shrapnel type round that was very similar in appearance to the Tromboncino only in a larger version. The Model 35 could produce the same effect of the Tromboncino with a higher rate of fire, a larger payload and a much longer range.

I would like to thank Arturo Lorioli of Rome, Italy for help with research and translation of the materials used in this article.

This article first appeared in Small Arms Review V10N10 (July 2007)
and was posted online on November 30, 2012


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