It is the Model 1842 and it is in .54 caliber. They were excellent, very reliable guns. Essentially, the Model 1842 was the percussion version of the earlier flintlock Model 1836, also a very good gun but of course subject to all the normal problems of a flintlock. About 24,000 of the Model 1842 marked that way were made by Henry Aston of Middletown, CT, from 1846 to 1850; 6000 more were made in 1851 and 1852 marked "H. Aston & Co".
A few of the H. Aston & Co. guns have navy markings and these bring about twice the value of the normal pistol.
1849 is the date it was made. Army inspector's initials may be on the stock, depending on how well it has been preserved. The Model 1842 was also made by Ira N. Johnson, also of Middletown, CT, in 1853-1855, with that contract being for 10,000.
A copy was made by the state of South Carolina at the Palmetto Armory; these are rare and costly. Only about 1000 were made in 1852, but many more have been made in later years by fakers re-marking the common Aston and Johnson pistols.
Value of a Model 1842 in average good condition runs $700-800, though one in excellent condition can bring $2000 or more. Barrels were bright, not blued.
Jim
