20gr shoot a little lower, not as accurate in any of mine, but that's just mine, doesn't seem to be any rhyme or reason, even tho all of the ammo is made in the CCI Lewiston plant, they certainly don't shoot the same, what shoots good in one of mine doesn't mean they shoot good in yours, I have 2 Marlin 917s, they don't shoot the same ammo!

I have to mark on the ammo box what gun to use it in.

I have 6-18x, 6-20x and 4-16x power scopes on my 17hmrs, they're accurate enough to use better scopes with a bit more power and an AO.

Check out Varmint Al's 17hmr page, he's got trajectory charts and more good stuff than anyone else on the net.
Tim
http://www.varmintal.com/17hmr.htm