As to trapdoors as surplus-
The number of stolen guns could have been sizeable in the period.Desertion rates assumed allmost heroic proportions,the peak was in 1871 when it reached 32.6%,8800 out of an enlisted force of aprox. 27,000+.
In looking in Frasca's Vol.2 there is a page in the appendix listing Springfield Arms sold by Schuyler,Hartley,& Graham.A lot of them were shipped to E.C.Meacham including .45-70 models.The first listing in that caliber TD was to Meacham,it's listed as sold Dec.3,1880-120 .45-70 Metcalfe(New)-120.There are two other listings that note the rifles as "New" in 1881 also shipped to E.C.Meacham,one order of 60 on Aug.1,and one for 40 on 8 Aug.
Adobe Walls-
Handgun Recoveries
.32 RF
.44 Henry
.44 S&W American
.44 Colt
.45 Colt
.50 Remington Pistol
Rifle
.44-77
.44-90
.45-70
.50-70
.50-90
.56 Spencer
Where and what-
Excavation of the stable-
1 .45 Colt cartridge
2 .45-70 U.S. Gov't.cartridges
1 .45-70 " " casing
Rath's Store
9 .45 Colt casings
1 .45-70 Van Choate CF casing
1 .45-70 U.S.Gov't casing
Myers & Leonard Store
4 .45-70 U.S.Gov't casings.
No cartridges or casings were found in the privy excavation.The surface finds were a .44RF Henry casing and a .56-50 Spencer casing.Two casings found which were of a slightly later date than 1874 were a .44 Evans Short CF and a .44 Long CF.
To account for the presence of the .45 Colt and .45-70 rounds you must take into consideration that the relief expedition from Dodge was furnished weapons by the Governor,20 Carbines and ammunition,and on Aug.18 the military was on site departing the 20th,and again in September after the hunters had abandoned the post.Lt.H.J.Farnsworth noting at the time that the buildings were still in good order.By late October the Indians had pretty much burned everything down.If the cartridges and casings were found in the burn layer it's good evidence they were there before late October of 1874 when the Indians torched the place.