Hi, Craig,

I wanted to say something, but since Sol mentioned dog barf, I let it go.

But, now that you brought it up I do use dog barf, usually in birds ~1.3" diameter and larger. My experience with it is that it appears to not block the flames and hot gasses well when used by itself; it needs to be used along with some wadding or a chute protector to work well.

I will often make a piston by placing a ball of barf in a sheet of wadding and putting that in first, then more wadding, shock cord, etc.

For HPR, dog barf with just a chute protector works well. For MR birds ~2" and under - whether it's dog barf, Quest wadding or crepe paper - I tend to get the best results when using a little Estes wadding in the mix

Doug
Hoping I'm not repeating myself...