Played around with magnum, standard, and bench rest primers today in a load that shoots fair in my .300 Win Mag. 125 grain Nosler BT's over 83.1 grains of H4831. The other day I put 5 shots in an inch at 100 yards with standard primers. These were the first 5 I loaded with this load after woorkin up to it. Today I tried the same load with all thee types of primers. I only had three rounds of each and all three loads were close to the same size except the ones with the mag primers put two shots makeing a wide single hole with the other shot off with an outside to outside spread of 1.4 inch. The BR primers made a triangle group measuring 1.365 and the standard primers made a horizontal strig of 1.6 inch for 4 rounds. I actually used 4 with standard primers first so the first could foul my barrel.

Now I realize this was only 3 rounds and one outing so it don't really prove much. However for me it shows that for the average shooter it probably don't matter what primer is used as for 125 grain bullets out of a .300 mag. these are not bad groups. The rifle I used has shot 4 shots under an inch at 200 yards for me with my deer hunting load of 180 grain BT's.

Just an opinion. With that much slow burning powder I would definitely use the mag primers. It will provide more dependable ignition on those days when the temperature is below freezing. It is said that one of the fixes for horizontal stringing like you had with the standard primer is changing the primer. Since you are not having a problem with the mag primers, easy choice.

Yes for this load I will most likely use the mag primers. Not important as far as cold weather as it will only be a varmint load. However I plan to try the same experiment with my 180 grain deer load before season starts.

Jocobite ----- I have loaded and shot my .300 Winnie extensively since 1973. My powder of choice is RL-22 and primer of choice is the Fed 210M, behind 180 grain North Forks or Nosler Partitions. I have tried all primers and it came down to the Fed 210M and the 215M, with the 210 giving one holers on my good days, with the 215 extending the group to 1-2 inchs. I have hunted all over the West and Alaska with this load from 20 below to 100 degrees and have never had a problem. I choose to use the match primers for all my rifles realizing that they may or may not make a difference, but for two bucks per thousand and shooting 3 to 4 thousands per year I figure I can afford that little extra just because it gives me peace of mind. Good shooting.

phurley5,
Others have recomended R22 but I have yet to try it. Like I said my deer load shoots very well but I like to play around at times and thought I would see what 125's would do. I had them as I shoot them in my .308. looks like while I am in a playing mood I need to try different brands of primers as right now I am stuck on CCI.

I tried two different primers yesterday -- WW WLR and Fed 210M -- with a load of 4831 in a 6mm Remington. The "non-magnum" WLR yielded 70 fps more velocity than the Fed 210M, however the standard deviation was similar (and very good) with either primer. 5-shot groups were also similar. The WLR loads SEEMED to be running slightly higher pressure (as the higher velocities would indicate), however not excessive pressures.

I think this illustrates that (1) Primers do have an effect on the behavior of the load, 2) Some "non-magnum" primers are fully as powerful as "magnmum" primers, and (3) switching primers may or may not affect accuracy.

I think I'll try some Rem 9 1/2, RWS Sinoxid, and CCI 250's with this same load just to see what differences/similarities I find.