Pictures are going to help if you can post them.
Is the receiver marked 1898 or 1899? Is there a sling ring bar  (or filler) on the left side of the stock? How long is the stock? What does the barrel band look like, solid or split, humped for sight protector? Hand guard? Serial number is May (?)of 1899 production. It would be at the very top end of '98 carbine production and unlikely. Number is surrounded by '98 rifles with out the hint of a rogue carbine! The number is also quite close to the beginning of 1899 carbine production.