Every gun likes a different size and type of pellet, so a 5.56mm sizer might be your best choice That way you won't make the pellets too small. In other words, if you aren't prepared to buy a whole set of sizers, don't bother.You could buy an adjustable sizer and spend some time figuring out what size works best for each gun.trrobb.com/product/adjustable%20pellet%20sizer%20177]https://www.trrobb.com/product/adjustable%20pellet%20sizer%20177[/url]
one thing to remember about pellet sizers.... they do nothing but make pellet smaller. Might be better to get a pellet gauge and see what size from the manufacture your air gun barrel likes.
Bill, you asked about where to find the pellet gauge. Its. Pelletgage.com