"a bit"? 57% of the regiments New York put in the field in 1862 were armed with Enfields. They were 37% of the weapons Maine gave its troops in the same year, 37.5% for New Jersey, 38.7% for Massachusetts, 30% for Wisconsin, 50% for Iowa, and 27% for Ohio. I bet you wouldn't call that "a bit" if it was coming off your salary. And these are just Enfields- remember what the Treaty of Paris, which all the major European powers had signed up to, said about shipping weapons through a blockade:
Enemy goods on a neutral flagged ship are not liable to seizure, with the exception of contraband of war.
It didn't seem "perfectly able" when Indiana tried to buy guns:
"the Governor, on the 27th of April [1861], authorised Calvin Fletcher Sr., of Indianapolis, ‘to proceed to the manufactories of arms in the Eastern States’... with characteristic energy and care, he prosecuted it in all directions that promised a favourable result. Some small quantities of our arms were procured, but the aggregate was too slight to make any special record of it necessary... several other agents, directly or indirectly in connection with other objects, made like ineffectual efforts to increase the State’s armament."
And things hadn't improved over a year later:
"Not a gun more could be purchased if all the Governors were in the market and the price doubled.” (P.H. Watson, assistant secretary of war, to OP Morton governor of Indiana, September 5, 1862)
As it happens, the US stepped up capacity as fast as it reasonably could under the circumstances. But even the most innovative American gunmakers found themselves calling on British resources:
“the 20,000 spoken of must be Colt’s contract, the most of which is for gun barrels, locks, and gun mountings, to be put together in the United States.” (FH Morse to William H Seward, 19 July 1861)
These things take time, and will taken even more if the biggest industrial power in the world suddenly isn't keen on selling you anything remotely resembling machinery that can be used to assemble weaponry.
Or, you know, if they launch a blockade preventing military supplies from going to the Union.