How to get partial seed

I have been growing since I was 16 born in 52. A friend of mine who was a big grower in the 70s taught me a trick on how to partial seed your plants if you want to get some seeds. I have alot od setivas and I want some indicas so what you do is get some of the pollen sacks of the male, put it in a baggie, wrap it around a branch tie it of in this case I used a rubber band for a short while like an hour maybe, take it off and hopefully you’ll get some seeds. Ive been doing it for years and it works.