It came across my mind when I read somewhere that someone used a magnum primer in a .308 and mentioned it made no difference in POI, pressure or velocity. I like to hear opinions about effects of using a magnum primer in a .308 instead of using standard large rifle primers.

The general rule of thumb is to back off a bit and work back up when you change a component. That said, I had a rifle that was giving me problems finding a load that it liked. I tried the most accurate load I had found and substituted a mag primer while leaving everything else the same. Accuracy and POI didn't change a bit. I have tried both LR and mag primers over the years and I honestly can't tell you one instance when a magnum primer made any appreciable difference at all. Unless you are near the top of the pressure scale I can't imagine that it would create a dangerous situation. But nevertheless I would still drop back a bit if substituting it for a regular primer. You never know ... it may cause a different accuracy node to appear.

I've noticed it can make a difference when using ball powders like Big Game in my 7-08, but made no difference on the extruded powders.

I use large rifle magnum primers for everything now just to keep it simple. I've heard the magnum primers help to keep velocity more consistent with ball powder in cold weather. In Texas, it probably wouldn't matter as much but in other parts of the country it would probably help keep velocity up and POI consistent.

Depending on a few factors, a magnum primer will equal about .3 to .5 grains less powder from a standard primer. It WILL increase pressure and speed, which may not be seen in POI at 100 yards, only further out.

Shows what I know, I always assume large and magnum rifle primers were different is size physically.
Learn something new all the time.

Large Rifle and large rifle magnum primers are identical in size and shape. If a rifle round takes a large rifle primer, generally, a standard or magnum can be used. You just have to adjust the powder charge accordingly. If it's a smaller case capacity round, and magnum primer is not needed. But it will still work.

Any magnum primer will be "hotter" than a standard primer. Some magnum primers are "hotter" than others. The 2 hottest magnum primers are the Rem 9 1/2 M and Fed 215. These need to be used for larger powder volume cases. I learned, that the CCI #250 is a classified as a magnum primer, but is almost in the middle between a standard and a magnum primer. Years ago I used to use the #250's with my 338 Lapua ammo. I had some hang fires I could not explain. I spoke with the main technical guy at ATK (the parent company of Federal, CCI, and others), and he gave me a lot of good technical data on primers. I switched to the Fed 215 magnum primers for my 338 ammo, and have not had a problem since. If the powder charge is larger than about 60-65 grains, I will use a magnum primer. I even use a magnum primer in my personal 270 Win ammo.

Also, when you step up to a magnum primer, the cup of the primer is thicker. The thicker primer cup can handle a hotter load, and have less chance of a pierced primer. I also use magnum primers in my 300 blk out super sonic ammo for the added benefit of less chance of a pierced primer.

Good stuff, thanks guys.

Learning experience

I use the CCI BR2 but I do not own any magnums anymore.

Great info, thanks

I use standard large rifle in .308, and even in the .300 win mag.