It is alleged that these pistol bullets will expand at low or subsonic velocites. Worked down a load till it went subsonic, the bullets went thru completly thru 2 pcs of 5/4" treated southern yellow pine and stuck or bounced off the third pce. No expansion at all at 30 yds, at 85 yds the groups were 4 to 5 inches. bolt action with a 6.5 twist.
Bullets expand due to hydrodynamic forces, without the hydraulic pressure to force the nose cone open, there may be enough force on the outside of the cone to keep it from expanding.
Have you tried milk jugs full of water, or at least soaked phone books? I know that gelatin is unrealistically expensive.
Shot a gallon jug and then a 1 litre water bottle, I am impressed by the results, then shot a small varmit 1 lb. version and it nearly cut it in two.
thanks for the eye opener.
I made a 2 sided with a bottom shooting box from pine boards 5" wide 4' long and filled it with ziplock bags full of water. That way the bullets expand thru the first bags and you can recover the slug. Worked pretty good for tests...Bob