Lead bullets obey the same laws of physics and air resistance that jacketed bullets do. Your Swede may have a 220mm twist, like mine does (a rebarrel job). That's one turn in 8.66 inches. It may also have a 190 mm twist (7.48"). Measure it.
After that, if you know the weight, length and velocity you expect to fire these bullets at, you can use
the barrel twist estimator at the JBM ballistics site to see how stable they are likely to be. To minimize the amount of twist per the weight and velocity, you want to look at something like a gyroscopic stability factor of s=1.4 or so.
You may want to consider firelapping the bore to smooth it for lead shooting. Be aware that if you switch to jacketed bullets after using lead, at high power rifle pressures that can cause a pressure spike. Also, lead seems to like to accumulate on copper fouling. Whichever bullet type you normally use, you really want to clean it out thoroughly before you go on to shoot the other type.