Vertical stringing cause?

[ssgross]

Assuming the bedding is solid and even under the receiver flat, and in the recoil area (behind the magazine), the next key area is the barrel band. It should fit snug so that it it won't slip off without light force...like a light tap with a wooden dowel, but not so tight that it binds. binding as the barrel heats up will cause problems. Full disclosure, I've never touched a carbine, but the bands on the krag rifle are very touchy indeed when fitting on new wood. The rear has more effect then the upper band, and it is the more difficult too, so I would assume the same principles apply to your carbine. A loose band will cause issues too - common in old tired original stocks. Easy to fix with a piece of felt between wood and band (on the underside, not against the barrel).

Check that your action screws are not contacting the sides of their holes. Looks like you have an original stock, so this likely isn't an issue.

Often, if the old wood is tired enough, the action screws might bottom out in their holes. Pretty easy to check by measuring. My first krag suffered from this affliction on the front screw, and filing off 1 thread was enough to make it shoot like a dream. Similarly the wood under the tang may be shrunk. cut some pieces of notecard to see if it helps.

Check your screw torque. I would say the krag likes no more than 30 inch*lbs, and maybe slightly less (28ish) on the tang screw.

Another guess... minor slop in rear sight. Sometimes they are just barely noticeably loose in the base. A brass drift and a very light, loving, tap will tighten it up. it doesn't take much so be super careful. A tap on the front edge, pushing toward the rear, will tighten up any minor slop in the windage, and a couple taps straight down on the rear part will tighten any minor slop there.

Lastly...shooter inconsistency. I don't mean to question you're ability, but it's a common enough problem for many when using barrel mounted rear sights with tiny peeps and narrow blades. On one of my krags, I can easily shoot 5 shots in <1in groups with 220gr round nose...the problem is it takes 10 rounds and I get 2 such groups!...one a few inches above the other! Depending on the weather, sunshine, or indoor lighting conditions, using a 6 o'clock hold with a "sliver of white" cleans it up, and makes a refrigerator worthy target after range day.

EDIT: a little non-permanent (blue) loctite on the band screw(s) may be a good idea. Sometimes the old threads are worn, and they back out when shooting unless you really tighten them...see first paragraph for possible affects.