Hand grenade “Odrin”

The “Odrin” hand grenade, designed by Col. Simeon Dobrevski in 1914-15, was spherical-shaped, filled with explosive and supplied with a fuze of remote action. It was adopted by the Bulgarian Army in 1915, and was intensively used throughout World war I. The body was built in cast iron and on the outside it had some square incisions, which, according to the intention of designer, had to aid the fragmentation, increasing the grenade’s deadliness, and to make it easier to grip by the soldiers. The outside diameter of the housing was 72 mm, the diameter of the internal cavity, where the explosive charge was placed, was 58 mm. The thickness of the wall of the body was of 7 mm, reduced to 4.5 mm on the incisions. The breaking of the grenade produced splinters large enough to put a man out of action.

In the upper part of the body there was a circular hole threaded to accept the igniter mechanism. When it was screwed up, a leather washer was used and the threads were usually coated with “artillery grease” to seal the grenade from moisture. Usually the body was painted black or varnished with a black lacquer. The charge of grenade consisted of 100 g Bombit, or 110 g of Balkanit.

Balkanit was mixture of 47% Trinitrotoluene, 49% Potassium Nitrate or Ammonium and 4% other substances, used to stabilize the mixture. In open air Balkanit burned quickly with bright flame emitting a thick black smoke, without exploding. But the explosion occurred if Balkanit, placed on an anvil, was beaten with a hammer weigthing 2 kg. from a height of 60 cm. Balkanit was put in little cylindrical cartridges weighting 110 g, 2.5 cm thick and 16/17cm length. Nine cartridges were collected into a packet (size : 20 cm long, 8 cm wide and 8 cm high; weight 1 kg.), and 25 packets were packed into a wooden box.

Bombit was a mixture of 79% of Bertholet’s salt and 21% of resins and oil. Under the action of heat Bombit melted, and its sensitivity raised. Left in the open air Bombit soaked up humidity, while it melted in cold water badly, and completely in warm water, since the oil appeared on the surface of the solution, and the resin precipitated to the bottom. A little quantity of Bombit in open air burned quickly with a bright white flame emitting a thick smoke, but it did not explode. The same happened if it was mixed with sulphuric acid. But the explosion occurred if Bombit, placed on an anvil, was beaten with a hammer weighting 2 kg. from a height of 40 cm. Bombit was arranged in cylindrical cartridges, weighting 1 kg, with a diameter of 6 cm and a length of 30 cm, 25 packets were packed into a wooden box.

The “Odrin” hand grenade utilized a new type of fuze that was ignited by a percussion cap. It proved more effective and reliable than the fuzes in use with the “Makedonia” grenades. The igniter mechanism was made of bronze and consisted of cap, body, fuze, percussion cap, and detonator. The main body of the igniter was threaded on the bottom to match the threading in the body of the grenade. For the explosion of the charge it was used the fuze N° 8 (length – 4 cm, diameter – 6/7 mm, charge – 2 g of fulminating mercury). According with the different source the maximum effective range of the “Odrin” grenade was 50-70 m, 150 paces (112.5 m), 200 m, or even 300 paces (225 m). Some “Odrin” grenades were modified to be fired by a mortirka, adding a wooden tube (cover-plate) and metallic caps.

The grenades were stored without the charge, and were charged at the mobilization or whenever it was ordered. They were supplied to the troops into wooden boxes holding 40 grenades each, and weighting 46 kg. These boxes were like the boxes of the cartridges. They were 67.5 cm long, 44.5 cm wide and 15 cm high. On the cover of the box the kind of grenade hold (hand grenade or grenade for “mortirka”) and the manufacturing date of were showed by a symbol and by a notice. Each ammunition pack animal carried 2 boxes (92 kg).

With the aid of a piece of paper or a funnel, the grenade was filled up with about 100 g of Bombit grated with a knife or 110 g of Balkanit, looking out that nothing fell down in the screw-cutting of the hole. After having put the fulminating mercury, the fuze was screwed on the housing of the grenade. In action the troops carried the grenades in special leather pouch, hung at a waist-belt behind the cartridge-pouch, or, in the absence of it, in the haversack during the march, and in the pockets during the combat.

Practice versions of the “Odrin” grenade were produced for training purpose. They were similar to the live grenade, but had 5 holes with a diameter of 1 – 1.5 cm, through the body to provide gas escape for the practice charges. The igniter mechanism anvil was steel to withstand repeated used, and the charge was a small paper cartridge filled with black powder.

The practice grenades were used exactly as the live grenades. Once used they could be picked up to have the charges replaced. This meant that new percussion caps, fuzes and charges should be fitted. To simplify the reloading the safety fuze was not coiled into the mechanism.

Technical characteristics
Type :	fragmentation
Size outside :	72 mm
Size inside :	58 mm
Thickness of the wall :	7 mm
Thickness near the segment :	4.5 mm
Weight of the body :	570 g
Weight of the fuze :	90 g
Weight of the charge :	100 - 110 g
Weight of the grenade :	760 - 770 g
Fuze delay :	7 – 8 seconds

Grenade Odrin	Fuze	Fuze wrench