only way I can see . No point having stock sitting and taking up space and costing money to store them if they can make say 1000 breech blocks then barrels to fulfil the order . if you have say a 1000 breech blocks and barrels of each calibre sitting waiting to be used its a lot wasted space. plus it will be stock that could be counted in a audit and cost them money ( I think that's how it works in the uk but maybe not in germany ).
"High Costs
Carrying excess inventory has significant costs. One of the highest costs for many companies is financing the purchase and holding of inventory. Also, the more inventory you hold, the more you have to spend on labor to manage it, space to hold it, and in some cases, insurance to protect against its loss or damage. Physically counting and monitoring the levels of inventory you hold also takes time and has costs."