NN and ordnance bomb markings on '42 SA Garand bolt and receiver

Found these two markings on a '42 SA Garand (699xxx) with Danish stock and one PB marked part:

Bolt: D28287-19SA B-18
The bolt seems to have an ordnance bomb stamped on it (never knew they did that). Any ideas?

Receiver is marked C19A NN 28291-17

What does the NN stand for?

Thanks

Never seen a bolt with that stamp on it ? Your revision 19 is too late for your time period. I would think a early revision 12 bolt would be correct, later in 1942 the revision 17 bolts appeared for a brief period (GCA article)