Stan's post (above) of William Brown is timely, because it is a mirror-image of "Freedom Gates" (posted by CSuniforms, also above.) One is obviously a "knock-off" of the other -- a forgery -- but which is which?
When one thinks of Civil War infantry firearms, Springfield, Enfield, Richmond (Model 1855 Springfields manufactured to 1861 specifications at Richmond using dies taken from Harpers Ferry Arsenal), Lorenz and Vincennes... all come to mind. On further reflection, the Sharps, Henry and Spencer company rifles and carbines are added to the list.
But, what was a "Belgian Musket?"
Upon review, it appears that a Belgian Musket was [my definition] "any European musket, manufactured in Prussia, Bavaria, Potsdam, France, or elsewhere, originally a smoothbore and with flintlock firing mechanism, that was acquired by Arms dealers (such as Herman Boker) and sent in bulk to Belgium (usually Liege) and there modified:
with firing mechanism altered from flintlock to percussion, and possibly
barrel re-bored (in attempt to standardize all that consignment, usually as .69 or .71 calibre, for ease of providing projectiles en masse) and sometimes
rifling added to barrel (which technically produced a "Belgian Rifle," but which was often still referred to as Belgian Musket).
Usually, the above weapons possessed no "maker's mark" (otherwise, they would be referred to as "Dresden Rifles" and etc.)"
Although the Belgian Arms industry, centered at Liege, also manufactured weapons, only the above "modified weapons, manufactured elsewhere," were referred to as "Belgian Muskets." For example, nearly everyone knows that Belgium manufactured Enfield Pattern 1853 Rifle Muskets (under contract before American Civil War; without contract during Civil War) and those "knock-offs" are still referred to as "Pattern 1853 Enfield," or, sometimes, "Belgian Enfield." [But the P-1853 Enfield manufactured in Belgium is never referred to as a "Belgian Musket."]
Just an attempt to add clarity to the muddied waters of Civil War weapons...
References: http://archive.org/details/Civil_War_Guns especially pages 66, 74 - 77 (Liege) and 28 - 35 & 262 - 271 (Boker)
http://www.regtqm.com/product-p/gun-646.htm just one of many "Belgian Muskets"
http://en.wikipedia.org/wiki/Lorenz_rifle not a Belgian Musket, even if modified in Belgium, because of the maker's label: Lorenz
http://www.ima-usa.com/products/original-british-p-1853-enfield-rifle-musket-produced-in-belgium-dated-1857?variant=26169131077 Belgian Enfield
http://www.researchpress.co.uk/index.php/firearms/british-military-longarms/enfield/p53-enfield-production-markings Enfields produced elsewhere
http://civilwartalk.com/threads/a-question-about-belgian-rifle-calibers.141769/ Belgian Musket and Rifle discussion at civilwartalk.com