Get in some range time with your hunting loads
It would be a good idea to pick up at least 3 boxes of different manufacturers 100gr ammo for your rifle. Head out to the range and find which manufacturer's 100gr works best in your rifle. Then plan on buying several more boxes of the one that your rifle likes. Try to never buy other Companies ammo after you have settled on one. It is amazing that shooters are sometimes surprized when the point of impact or group size changes drastically after swapping to a different manufacturer. Ammo for a rifle is not like gas in a car, the rifle will behave differently if you change it. I always worry when I see someone shooting the last of their ammo up prior to the Deer Hunting opener. They usually say I have to go pick up some more from the store. I just hope for their sake that the store still has on the shelf exactly what they were shooting. There is a lot number on the inside flap of a box of ammo, many shooters will check to see that the boxes they just grabbed off the shelf are the same lot. Companies tool up for a run of a cartrige and then loads thousands of rounds. These are then boxed up and all given the same lot number. Two rounds out of different boxes with the same lot number are identical. Let us know how things work out with your 243. If shooting ever starts feeling like work you are doing something wrong.