That would depend on the bullet you are wanting to use and speed needed for it to perform. I personally don't like pushing single lug Krag actions too hard, so I load to have a 150 yard shot on deer using std. Hornady BTSP's. Per Hornady, you need to hit with at least 1600 FPS at impact, so I worked backwards using quick load. The load I settled on was 28 gr. Reloader7 with the 180 gr. Hornady BTSP and it's set for up to 150 yards max. Maximum load per my data is 34 gr., so it's still a very safe level and lets the old girl bark enjoyably.
***edit***
Sorry should add here that reducing barrel length would have to be determined as to loss. In the load data I have, you'd need a full house load to keep velocities high enough for bullet performance. As a general guide, you lose 50FPS per inch removed, but that varies some based on powder. If you know someone with quickload, might be worth running some numbers.
