Re: Help w/ .243 ...
This is a difficult thing to answer...
This is what a generally do to get folks started when they elect to use factory ammo.
First do a complete check of your rifle, everything tight (stock screws, scope bases and rings) and in the psition you want it to be in for a long while.
Go to a WELL stocked store and buy a box of several different acceptable types. Try to avoid buying ammo that is low in stock (only one or two boxes). Take these selected types out and shoot them and determine which the rifle likes (it may like the most expensive variety... some guns a like that... just like women). Once you know via direct results, rush back to the same store and BUY ALL THE REST of that particular ammo of the same LOT NUMBER... now your set for a while.
It may be a significant outlay to buy all the remaining LOT NUMBER of ammo at first but it's not an outlay you're not going to make over time anyway... If you don't buy a significant number of boxes you'll probably need to go through this same "buy and test" procedure more often than you'd like.