I have seen a heck of a difference in primers ......
when dealing with super accurate custom guns. Funny how a particular powder will love a particular primer to get those little tiny holes in the paper.
Rem 7 1/2, CCI BR-4's, and CCI450 all have thick cups, and in my loads the CCI450 is the hottest, but is not always the most accurate.
I'm a new convert a couple of years ago on Vit N-133 with the 40's & 50's, and Vit N-135 for the 55's. Out of my 26" Hart barrel, I can get 3900-3950 out of the 40g NOsler BT putting all the bullets into a tiny hole. With the 50's, using the 133, I am getting 3600-3635 out of the 50's, into the same very tiny groups, and with the 55's with the 135, I am getting 3550 with groups less than .300.
All of these loads are high pressure loads but will not require full length sizing of the brass, but will demand a thick cup primer.
I use IMI and Lapua brass with a minimum SAAMI match chamber with a .250 non turn neck with .2245 thoat and 1 /1/2* leade angle in 14 twists.
When I was playing around with the loads, some loads with the 133 had a slight edge with 7 1/2's while others liked the BR-4. All of these groups were in the .185-.250 range shooting Nosler BT bullets. The groups opened up slightly with the 450's, but not by more than .030.
Win and Fed 205's have very thin cups.
If I were shooting in super cold weather, then I would use the CCI450 or the 7 1/2 in that order. Remember that in temps of -25* and colder, pressures can spike!