I don't see any recorded evidence suggesting variant projectiles were used in the Whitworth Rifles. Col. Beimeck's coverage of the topic is thorough and seems complete. There are just a few conclusions about CS production and their usage that I have learned from my years of handling examples and studying the records that are worth noting. First - I think that all the Whitworth guns were breech-loading when imported. The ammunition was supposed to be "fixed" using a shaped tin can like the example pictured below. During 1862 and 1863, the Rebel artillerymen fired fixed rounds. A "lubricating wad" or "lubricator" was positioned between the charge and the iron shell bottom for obvious reasons. Many of those tin cans might have come from England with the gun barrels and limited quantities of shells. But there are contemporary letters to the CS purchasing agent in Europe to avoid buying any items like carriages, implements and ammunition that could be made cheaper by Southern manufactories. After reading the Col's Whitworth section, I realize that this particular tin cartridge could have come more recently from South America or England. I do believe the South made some, I just don't have absolute proof right now. But they clearly used them.
Is there any proof that Sir J. Whitfield exported muzzle-loading guns? I have found convincing evidence that the Whitworths used at Fredericksburg and Chancelorsville fired "fixed" rounds employing these shaped tin canisters, and I strongly suspect that the two guns (the same two guns) fielded at Gettysburg remained breech-loading. However, the several 1864 invoices from the Fayetteville Arsenal to Petersburg, where they were used extensively, do not include any of the tin cartridges or references to fixed ammunition. I believe that was because the CS Ordnance officers had decided to convert the guns to muzzle-loading by the spring of 1864.
The second item below is an August 18, 1862 letter from the Fayetteville Arsenal to a CS agent ordering him to pickup a Whitworth gun with carriage and implements to bring to Richmond. It was from the blockade-runner Modern Greece and included "as many rounds of "fixed" ammunition as can be spared." I assume this refers to imported British rounds but its possible they were finished rounds supplied by Fayetteville earlier. It appears that this was the first Whitworth gun sent to Virginia and fired from the heights along Mine Road (i.e., the green water tower today) at the Federal batteries posted along the Old Colonial Road where several bolts have been dug (by friends of mine). The second Whitworth gun was sent to Virginia by the Augusta Arsenal in late March 1863 and used at Bank's Ford by Hardaway. Tucker Williams dug four intact projectiles - all made by Augusta - shells with ridged (star cavity) interior. I believe these were the two Whitworths sent to Gettysburg.
The third item below is a December 1862 invoice from the Fayetteville Arsenal confirming the shipment of 420 Whitworth projectiles, lubricators and tin canisters for the guns at Wilmington, NC. The vast majority of Whitworth ammunition made by the South came from Fayetteville. Their Whitworths are the "long" pattern identified by Col. Biemeck. Fayetteville had a machine for finishing them acquired from the inventor in England. Augusta made a shorter projectile using a bolt as a mold pattern. So all of theirs are the same length. They hand finished using lathes and probably a grinding stone.
The 4th item below is a Fayetteville invoice including Whitworth canister rounds with copper bottoms. They are mentioned on other invoices. I believe that Fayetteville actually made these but they might have arrived on a blockade runner. What a rare item this would be for a serious collector's bucket list.
Enough for now,
Woodenhead