Don't worry too much with comparing the dimensions of the SAC-approved C.S. Macon carbines. Those dimensions ONLY apply to reproductions of C.S. Macon 'Razeed' Carbines not to original specimens. But even with that caveat while there exist descriptions of the "razee" carbines produced by Richmond Armory as well as numerous extant specimens that can be compared with the standards implemented, we do not have any such documentation on the muskets salvaged by at C.S. Macon Armory, or any exact quantities.
While there are hundreds of examples of both wartime "razee" carbines and muskets cut-down into shotguns in the post-war era, still other cut-down muskets as so-called 'cadet' guns, little information survives to the identity of such examples. I have seen (and own) numerous examples of both M1816 muskets and M1842 muskets that have been reduced in length, some even having had the barrels re-tapered for virtually the entire length so as to accept a socket bayonet (a modification having little use for hunting or sport), no one can guarantee with any certainty whether these muskets were actually altered during the war.
Although some have suggested how such modifications may have been done to make-up a "cadet" version or possibly for veteran's ceremonial use, seldom do we find more than one extant specimen to clearly establish any uniform or standard pattern was in use had it been done for a cadet academy or ceremonial use. Certainly there are such examples of "cadet" models made-up by Bannerman these were also advertized in his catalogues so we at least have an idea of what those guns looked like as well as still others made either in reduced proportion or lightened in weight by the Liege trade but these examples are not those that I am referring.
It's one thing to find examples of cut-down muskets which have had the barrel and stock shortened, and the front band moved back, either leaving the middle band with its swivel intact or eliminating the band entirely. Some of these include "Special" model arms that were modified by the national armories at Springfield and Harpers Ferry, such as the now popular Fremont rifles that were cut-down versions of the Model 1842 rifled musket. However, other examples are occasionally found which have had the barrel re-tapered to accept a socket bayonet fall into an unknown category. They have the appearance of a military arm because they are equipped with a socket or sword bayonet, yet, are not so uniform in appearance to be such because in many instances there is a great variety of barrel lengths and also model types. Such examples of this type are pictured in the link below, and do not necessarily conform with the SAC-approved examples.
viewtopic.php?f=4&t=13647&p=53129&hilit=richmond#p53129 (
http://n-ssa.org/phpBB3/viewtopic.php?f=4&t=13647&p=53129&hilit=richmond#p53129)
According to the late Howie Madaus who in 1990 examined the Remington-Maynard conversion pictured, he believed it to be one of the salvaged muskets altered at Macon, and had my 35-mm camera's internal thru-the-lens light meter not been 3 f-stops off and had I been able to have supplied him with a good photo, it too would have been illustrated in Murphy and Madaus (1996) Confederate Rifles & Muskets just as was the one that is illustrated as supposedly altered at New Orleans with the sword bayonet bar (at top of p549) from a private collection formerly in Marietta, GA. It's the one allegedly fitted for a Cook & Brothers sword bayonet, or shall we say, it will fit a C&B sword bayonet or a Pattern 1856 Lancaster sword bayonet, the sword bar only accepts a very narrow slot and will not accept the later Pattern 1858/60 sword bayonet.
The other example below it (from the Milwaukee Public Museum), has a 28 ½ inch barrel that was re-tapered to accept a socket bayonet, and is equipped with a bayonet stud on the underside of the barrel, evidently to accept an 1842 socket bayonet, while the stud for an M1816 is normally located atop the barrel. On page 443 of Confederate Rifles & Muskets features a Model 1842 musket with a 34-inch barrel, and is like one of the SAC-approved specifications for the 34-inch Macon carbine or musketoon. It is fitted for socket bayonet. The specimen as featured on p445 is very similar to the Model 1842 shown in the link, where the front band has been moved back and the band spring re-inletted about an inch forward of the middle band spring, and which is fitted for a socket bayonet.
Clearly such examples as these considerably more advanced tools and special knowledge to deal with the added complexity of these modifications. It also required use of a metal lathe to re-taper the barrel, evinced by "dog-marks" scattered over the barrel surface. But were these examples made or modified during the Civil War? While correspondence is found relating to the cavalry carbines utilizing U.S. Model 1842 musket stocks, there is no similar correspondence regarding the Model 1816 musket, nor was there any attempt to manufacture replacement Model 1816 stocks like there was Model 1842 stocks and even though there was stock machinery to make the latter, certain parts had been lost in transit such that without those parts new stocks could not be produced. Consequently, no Model 1842 stocks were manufactured at Richmond or Macon during the war.
While Davies' book on Richmond Armory provides a myriad of documentation on the Cavalry Carbines in both .69 and .58 caliber, including documenting the 25-inch barrel length of the rifle caliber version and addition of a rear swivel in the butt, other than the extant examples of these two models, it is merely assumed that these constitute a official pattern. However, the exact pattern of the Macon "razeed" carbines is rather vague in the references made to them in official correspondence.