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

[Burtonaxe]

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

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