Starrbow; As a rule of thumb, the more spin (or excessive spin) of a given bullet in a given twist, "reduces" LATERAL kinetic energy, and therefore reduces destructive power, instead becoming ROTATIONAL kinetic energy, increasing gyroscopic interia, which would support your findings. I would not expect the 1-20 in my 444 to have the same effects as the same bullet weight/velocity in your 1-38, if all other conditions (and there are many to take into consideration) were exactly the same. I am not a ballistics engineer, but, that is the way "I" understand what you have presented, but, this is WAY beyond my ballistic expertise!!! How much of a benefit or affect the 1-38 twist would actually provide on game animals under field conditions over the 1-20 twist as far as "penetration" capabilities is anybodies guess. My guess would be that either/or would produce one big hole in, and one big hole out, although the efficiency factor of one twist over the other may vary. I think that this would be a question, or a test for somebody like James Gates, who has the knowledge, training, and experience to come to a scientific conclusion.