I have a Remington model 700 Classic Stainless with a 22" barrel. I purchased the rifle 5 years ago along with 2 boxes of Federal Premium 120 gr. Nosler Partitions. The rifle averaged 1.25" 3 shot groups with this ammo. I have concocted a handload using the Hornady 117 gr. Boat tail spire points that will group .875 for a 3 shot group on average. I also load the 100 gr. Nosler Ballistic tip with 50 gr. on H4831 and get honest .375 groups on average for 3 shots. I have not handloaded the partition in any weight for my 257. I would definitely say your gun doesn't like the 120 gr. partition. It is peculiar that you can shoot the Sierra so well. I say this because with the groups you were shooting it doesn't seem that your bullet is stabilized. This could be because of a 1 in 12 twist in your rifle barrel. This doesn't seem to be the case if you can shoot the Sierra and the Hornady. Most guns if they don't like a particular load will still group much better than 12" at 100. Some of my terrible loads would still shoot 3-4" at 100. I would use the bullet that you are going to and stay away from the partition. Good luck and good hunting!!