Has anyone used these in a Crosman 1077?
I'm shooting indoors on paper and plinking targets. I'd like to avoid dust. Will these pellets shatter when shot into a standard metal pellet trap or will they deform but remain intact?
They will deform.
Stick some rags inside the trap and then it won't matter. (and it will be a lot quieter)
What is the pellet material made of? Is it pure or an alloy?
mostly tin. USA Shooting team tested these and found them accurate.
Are these pellets allowed in sanctioned competitions?
sure, no competitions out there make restrictions on the material used in a pellet. You can shoot paper spitballs if you like as long as it's safe and gets you the gold medal go for it!
It would depend on the competition and its specific rules. You would want to ask the competition organizer.