Hi,
If you want to restrict the user for issuing the components to production order which should not be more than the quantity specified in BOM then you should follow the SAP standard way like as shown in below screen shot. For example in MB1A transaction, enter Movement Type, Plan and clik on tab/button 'To Order'. You will get 'Reference: Order' screen wherein enter Order Number then Click on "Adopt+Details" tab, as shown in below screen.
If you follow above process then system will record the issuing components to order because you have entered the reference order.
But many time user enters Movement Type, Plant and then press Enter without click on "To Order" tab. This is wrong way. By this way system can not record the issuing components for reference order. If you follow this process then you issue more than BOM component quantity.
Hence by using ABAPer, make the 'Reference Order' screen mandatory.
Above is the way you can proceed and if you want to issue with respect to tolerance limit then by using ABAP help you can apply the logic wherein you can restrict the user either at Goods issue transaction or in Production Order Create/Change Transaction.
Regards,
Narresh