A quick story so no one does anything as stupid as I did.
I was issued a beret that seemed way too big at the time but I was assured by the leading seaman it fit great.
My buddies told me otherwise so they took it from me, cut the liner out, made me shave it, soak it hot water, and then slapped it on my head. All of that went great except that the flap was still down over my ear.
I decided I needed to shrink it. I threw it in the dryer on hot hot and took it out. The only real difference was that the leather band seemed awfuly tight. This is where I get stupid.
After getting frustrated over it I soaked it for a couple minutes in a sink of steaming water, then put it on a plate and put a big plastic microwave cover over it. Into the microwave it went. I set the microwave for 5 minutes, figuring I could judge how much it would shrink after that and walked away. After two minutes I heard a crackling sound and ran into the kitchen to find steam pouring out of the microwave. I freaked and opened the door, catching it in the face and burned myself taking the beret out. To my horror I saw the leather band was about 6 inches across now. I grabbed it to stretch it and burned myself again. I grabbed some oven mitts and started stretching it back out. I figured I should get it on my head so I threw it on without realizing the material was still soaked with now boiling water. Can't say that felt too great. I spent the last couple days trying to keep the leather from shrinking smaller and smaller as it dries. Today when I got home from school I stretched it and heard a 'crack'. The leather split, but thankfuly it's under the flap where it can't be seen. I know I will catch hell for it anyway. At least my beret is no longer too big, however I am remided of my own stupidity every time I wear it because it squeezes the crap out of my head.
In conclusion, if you need to shrink a beret a bit, stick with the dryer.