The .30-40 Krag cartridge 'head-spaces' on its rim. It is normal in necked-rimmed cartridges, like the .30-40 Krag (and even more so with the .303 British), for the factory cartridge case shoulder to 'move forward' and form to the chamber. Your fired cases don't look that unusual to me.

As I have mentioned elsewhere, when you reload your .30-40 brass, back off the F.L. Sizing Die, a turn or two, and neck-size only. There is no point generally in F.L. resizing .30-40 brass if used in one rifle.

It is possible that the 'gun-smith' who 'Sporterized' your Krag followed an old practice of lapping its locking-lug so that the rear of the bolt guide rib now makes contact with the receiver, when the bolt is closed.

This practice was believed at the time to strengthen the action. (As built by Springfield, the bolt guide rib has a few thousandths clearance at the rear).

The practice of lapping the Krag bolt lug for this contact increased 'head-space' by a few thousandths. (Unissued replacement bolts are available for $55 on ebay and will tighten up 'head-space').

Testing the bolt fit in the receiver requires just using the bolt (with out striker assembly). 

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