These might be repeat questions and if they are I apologize but after searching around a while I could not find the info needed.
Does anyone have ballistic info for prmi partizan 75 gr ammo for a Colt 6920? I would like distance drop off charts if possible.
How much will my zero be off if I switch to less expensive 55 gr ammo for practice/fun shooting?
If I used two different scopes, one for 55 gr and one for 75 gr ammo, is there an attachment that allows me to exchange scopes on my AR without having to re-zero?
I plan on sighting in at 50 yards if that makes much of a difference.
Try a search with ballistic charts / zero here, or find a ballistic calculator on line.
They will get you in the ballpark and you should confirm data on the range.
As for scope mounts, there are repeatable zero mounts, that are accurate to a certain point. Even though I have found some to be repeatable within the claim, I do not rely on such repeatability in regards to distance shooting for a precision rifle / optic. As for swapping optics, you could just acquire data on different ammo types and dial accordingly. If you ever find yourself in need to actually have to dial differently for different ammo types.
My intended use for the rifle will be 3 gun competitions although I would like to be able to take long shots for fun. I typically shoot handguns and am obviously just starting with ARs so any info is handy.