Before you go buck wild and start swapping bolts/carriers, you need to think about roller sizes and B/C gap.
The way a G-3 headspaces is determined by the roller size in relation to the face of the barrel. No headspace gauge is going to tell you if the headspace is correct. If the barrel is set up to bolt gap with a standard roller size, then when you install a bolt with over size rollers; you have increased the bolt/carrier gap on lock-up. The standard working Bolt/carrier gap .008 to .012 between the two with the carrier locked against the bolt (action closed with the hammer down). By increasing the gap with an over size set of rollers, the bolt unlocks too soon and you get severe recoil.
FYI: The way the rollers work on a HK is that they make the bolt/carrier act as if they are heavier that the actual weight (think blow back action). The force of the fired ammo forces back on the bolt, which forces on the roller, with the mass of the recoil spring and carrier weight keeping the rollers in the locked position. At a given point of back pressure force from the fired round, the bolt forces the roller back into the into the bolt (unlocking them from the trunnion and allows the bolt to unlock and be driven back with the carrier. The HK uses a buffer (in the butt stock to absorb normal recoil, but not that of an action opening up too soon due to the having the B/C gap-relationship out of spec. Also, since the factory spec gap is designed around Nato ammo, by going with ammo that has a heaver bullet or stronger load, the action tends to open up too soon, which in turn, causes the rifle to have a stronger (above normal) recoil that the buffer will not tame.
By going with an excess B/C gap (oversize rollers), you have just lighten the overall geometry to keep the bolt closed under recoil, hence made the bolt unlock too soon during the action cycle.