It is not really a Remington. About 1855, the government contracted with Remington to provide 20,000 Maynard primer locks to Frankford Arsenal, which used them to upgrade Model 1816 flintlock muskets to percussion rifles. Frankford also rifled the barrels and fitted long range adjustable rear sights (the Model 1816 has no rear sight). Many were used in the Civil War.
My older Flayderman's gives a value in good condition of about $1800; I would guess at a current value of $2500 or more if in good functional condition.