IA culpability lies in the fact that they knew OFB could manufacture the barrels and maybe some other parts as well. They also knew about the upgrade to 45 cal solution. Someone should have taken the lead and said why not try to develop an indigenous gun, by developing some of the missing parts. As recent history has shown, it would not have been that difficult and we could have had atleast a Dhanush type solution or at the very least a Bofors clone with a 45 cal barrel by around 2009-2010. But sadly enough, IA and MoD never acted on this.
The above topic was discussed in DFI as well. Kunal (Dada!) asked his OFB sources, and had posted some information. Also, from compiling various info around the internet, the conclusion was something like this (from memory so pls excuse).
Barrel tech: given by Bofors in 1980s and worked fine.
Breech tech: Bofors tech given in 1980s was not good, so final good working solution was obtained from Soltam around 2007 during the 180 guns ToT. (Breech is attached to barrel, and shell is loaded here. Has to withstand same/ greater pressure than barrel. Has to provide gas tight seal of corrosive explosive gases. Has to incorporate firing mechanism. Has safety features so operators fingers, etc. not caught when breech is closed.)
Some other critical stuff: desi efforts by our people. An EME Technician fabricated a critical part out of local available steel, called a "Breech Ring 155mm". He was given an award, for Import Substitution for this by NaMo himself. About 6 OFB/PSU Factories worked on building the Dhanush, aided by private sector firms for stuff like hydraulic cylinders, APU, electronics, wheels and tyres, sighting and elevating mechanism, etc.
Courtesy Indian Express: Indigenisation of components of 155mm Bofors gun
Every year 200 gun ring kits are required for the 155 mm Bofors gun. Each kit costs Rs 1,60,000. Due to unreliable supply, a need was felt to achieve self-reliance in manufacture of these kits. Indigenisation cost of the kit is Rs 55,800.
Developed by Subedar Arjun Kumar Jha, who was enrolled in 1991. Has served in active field areas of Northern and Eastern Sectors. Has been associated with Bofors gun since past 10 years.
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