For years, I shot a 490 grain Christmas tree bullet in my Shiloh military carbine with 50 grains of 2fg GOEX.  This load just fit length wise into my chamber.  I then had a custom mold made that weighed 350 grains and when I put the same paper tubes with the new bullet into the chamber, there was about a 1/4" space between the bullet and the rifling when the paper case was placed at the breech face.  Poor accuracy resulted.  When I pushed the cartridge forward into the rifling, accuracy returned and I still had reliable ignition.  I just have to use my finger to push the cartridge forward in the chamber.

Good evening, I have a Shiloh .54 1863 military percussion rifle that was made in 1986 in Big Timber before the Bryan purchase.  Fantastic rifle.  I use a Steve Brooks mould made specifically for Charlie Hahn's 1.5 inch hard paper tubes, loaded with 62 grains 1.5 Swiss and secured on the end with ladies hair curler paper (my lovely bride is a hairstylist).  I use clear fingernail polish for the 1" X 1" hair curler paper square which is attached by sliding the tube over an aluminum rod 1/2 inch mandrel from Ace Hardware.   

The bullet base is engineered to fit into the tube.  This bullet and charge closely duplicate the original charge per U.S.Army records during the War Between the States.

Charlie Hahn tubes are available for purchase from Shiloh or from his website which can be reached via Google for Charlie Hahn machine shop.

I have not tried loading loose powder and breach seated bullet as I have heard that it may contribute to gas plate erosion.   The loaded Hahn cartridge is easy to construct and when loaded in the chamber is about 1/32 " from the breach.   

I experience excellent accuracy from this cartridge.  1860 ordnance tests proved the cartridge with the flat base was superior in accuracy to the folded base cartridge that required shearing off of the tail by the breach closing.

This is an exceptionally fascinating rifle to shoot and I usually experience about 2 moa in accuracy, which is probably the limit with the barrel sights and the tiny front sight, which is challenging for half century eyes.

Good luck!

Matt