6.5CM ammo help

[loki]

I recently bought a 6.5CM Bergara, mounted a 6-24x50 Vortex Viper PST, put all the trimmings on it and zeroed it in with a 143gr load. I was curious about other grains so I bought a few others, 127gr, 140gr.

After zeroing it and getting a constant grouping at 200yrds within 1" I changed ammo....Everything went out the window. Grouping was within 4" at best at 200yrds.
I checked a ballistic calculator for the new loads and adjusted as directed and it seemed to work but I didn't like that it was that big of a change at 200yrds.(143gr and 127gr). I know there is gonna be a difference but that much at 200?
Has anyone had this problem? I want to get custom turret caps made for it but I guess I'd need 2 or 3 of them to be any good. Or is the 6.5 a "pick a grain and stick with it" caliber?

[Delfuego]

Or is the 6.5 a "pick a grain and stick with it" caliber?

Yep!

I wouldn't even pick a grain (weight). I would pick a bullet, brand, and then lot#. With commercial ammo I have seen terrible inconsistency. It has more to do with bullet shape and velocity that weight. I would buy a box of each, shoot groups, find the best, and buy a few cases (at least) of it.

[loki]

That's basically what I'm doing, and planning to use it hunting so I guess 143gr sounds best. Thanks for the help.