You may need to adjust your loads, try different bullets, or as Madsenshooter said... do some work on fit.  You really shouldn't have a problem using the sling as it provides you a stable third point of support when shooting prone.  Bear in mind - if you intend on using the Krag for CMP match shooting, especially at Camp Perry, you can NOT glass bed the stock in any way!  At the Roosevelt Match last year, they were checking trigger pull and spot-checking some rifles for bedding and other modifications.  If you medal, they will absolutely check!