I'd try all of them with the same loads to see which gives better accuracy. Primers do make a difference there. All are magnum primers and for big cases of powder, especially ball powder, they are usually recommended.

In my experience there is not a lot of difference between CCI and Federal.

Match primers tend to be more consistent from lot to lot and within a lot. So you might notice a difference between the match versions of CCI/Federal and the none match versions you listed.

I just got some Remington primers in a trade out with supplier--one box of 1,000 is labeled Remington 9 1/2 M Magnum Primers. In the past I have always used CCI mag primers and am not familar with the M designation, as opposed to Magnum Large Rifle--any info appreciated.

Remingtons designation for large rifle primers is 9 1/2. The magnum version simply adds an M.

Thanks Don--That is what i thought but other manufacturers do not add any letters to their primer #'s or names.

You will probably see no difference from brand to brand. There is a difference in standard and Magnum, however. For the 300 Win Mag always use the Magnum primers whatever brand. If the temperature is going to be lower than 32 Degrees F., I believe you should be using them on hunting loads no mater what size of large caliber rifle ammo you are loading. I make it a habit to work up all of my large caliber hunting loads with the Magnum primers.

As someone else said accuracy is the reason for trying different primers as with all other components.

For example I recently made eighteen reloads of an identical load expect for the primer. For nine rounds I used a Rem 9 1/2 pushing a 55gr HPBT with 34 grains of Varget. I made another nine with the only difference being that I used a CCI large rifle primer in the those.

With the Rem I would get two almost touching and one flyer each time resulting in about an 1 1/2 inch group for a three shot group.

With the CCI it went under 1/2 inch each time. My 22-250 liked the CCI better with all other things being equal.

SocoKHntr wrote:
" With the Rem I would get two almost touching and one flyer each time resulting in about an 1 1/2 inch group for a three shot "
That doesn't sound like a primer problem to me, sounds more like a barrel getting a bit over temp, if the third shot is the "flyer"
Good to see ya up in Reloading ,rumor has it that they were picking on you down in Political Section, glad you escaped

Hey, thanks Hammer, I think it was the primer as all other factors including cool down time for barrel betweens shots was the same.

I haven't changed primers, or bought any, in probably ten years, BUT, if the primers are all from the same lot, stored together, etc....powder deterioration..?... I just don't know
Maybe some of the old guys will know