I don't know what the minimum speed for expansion would be but I do know that when I tried to push them 3800 fps and above in my 220 Swift they would get out to between 75 and 125 yards and sling themselves apart. I would just see a gray puff in the air. In my 223 Rem. they would really do a number on ground hogs out to 300ish yards.
I sent an email to sierra and they told me that about 2000fps.
I think a high speed for a varmint bullet.
I expected around 1500 fps
I run them from my 22-250 to 3500fps.
it is a low speed for this caliber, but they group phenomenally and the brass is more durable, as well as the life of the barrel