The barrels were in fact free to the prime contractors that did not have the capability to manufacture barrels. The minutes for the September 1943 Inspection Council Meeting calls them Free-Issue Barrels as do many of the other various carbine meeting minutes. The government contracted for such barrels and they were provided in quantities specified in the individual contracts. As an example, Rock-Ola's contract was initially for 145,000 carbines, with spare parts (which consisted of ten spare barrels per 100 carbines) and an additional 161,409 barrels & gas cylinder assemblies at $6.00 each. So those barrels were not as you say "excess" they were a planned manufacture to be used in the Barrel Free Issue program.

Other parts that were transferred between prime contractors to keep production rolling were not free nor paid for by the government. Like stated earlier they were paid for by the requesting contractor. The best known example of this was Winchester's resistance in taking the left over receivers from Underwood since they (WRA) could produce the receivers cheaper than they could be purchase from Underwood. The C.I.I.C. stepped in and was successful in negotiating a deal in which WRA paid Underwood what it would have cost WRA to produce the receiver.