I tried using n2 on the basis that the field is supposed to be twice as long

'N' is a unsigned 32-bit (4 byte) value using the same byte ordering as 'n'

'Q>' is a unsigned 64-bit (8 byte) value using the same byte ordering as 'n'

From the info you gave us, you want 

unpack 'a a n N Q> a*'

[download]
which can also be written as 
unpack 'a a S> L> Q> a*'

[download]

That said,

I know from the output of the other program that the ClOrdID in this message is "4295075805"

The long string you gave for ClOrdID translates to 04C6A29EBAD1E5BB(base16).

You're expecting 4295075805(10) = 000000010001A7DD(16)

No matter how you rearrange the hex digit pairs, those will never match. It's clearly not a byte ordering problem.

In reply to Re: Lost in unpack hell by ikegami
in thread Lost in unpack hell by stevehicks

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