The first thing to check is always the magazine cut off. If missing or modified it will cause problems and or damage the cases.

Not sure if any one here has a list of similar threads, a lot can be learned by reviewing the other similar problems and solutions. Using the search function will find many of them but specific wording will catch or miss a lot of the threads. Using google or Yahoo search with KCA in the search line will find even more references.

'BillBlab' - Welcome to the KCA Forum.

The 'truth be told' the U.S. Krag was designed to feed cartridges with a 220 grain Round-Nosed Bullet, seated to an approximate, 3.089 inch, over-all length.

The position and slope of the case-shoulder, also plays a role in the smooth feed of cartridges.

Many U.S. Krags are tolerant of different bullet profiles and shorter over-all cartridge length.

Sometimes changing the left side-plate can make a Krag more tolerant in feeding non-standard rounds.

When a cartridge is 'short', it may move forward in the magazine. When the bolt makes contact, with the rim of a cartridge that is too far forward, the case shoulder can hang up on the lobe on the interior of the side-plate.
This can cause a jam or the cartridge to 'dive'.

Bullet profiles, like 'Spitzers', can hang up on the rear edge of the barrel-breech.

Some Krags seem to eat anything.

Tell us more about your 'dummy' rounds.
Pictures of everything always helps solve a problem.