How much powder is a magnum primer worth?

[GUHunter]

Close to getting a load finalized for my tikka 6.5x55. Using ramshot magnum, and 140 grain interlocks. During load work up, I never got pressure signs before running out of powder space and while it was accurate I wanted to experiment and try magnum primers. Switching from standard large rifle (federal) to magnum large rifle (cci), I started by dropping down 3 full grains of powder and working up from there. The starting load flattened the primers (very flat). Remember that I saw no pressure signs with the standard federal primers and an additional 3 grains of powder. Does this make sense? It surprised the heck out of me.

[j_h_nimrod]

I have seen this on some tweener cartridges where you can go either way with a primer. My theory is that the more rapid burn from the mag primer spikes pressures and causes the primer deformation. I usually use standard primers unless I start getting erratic ignition. The best accuracy I typically get on the tweener cartridges is with standard primers, when I have switched to magnum I typically loose accuracy.

Personally, I would not use a magnum primer on anything not burning a lot more power than you can cram in a 6.5x55. If you want more speed (I assume that is what you are looking for with the mag primer) I would switch to a different powder.  You didn't post velocities before and after primer change so I am not sure if your flattened primer is indicative of higher speed.

[jasnt]

Personally I would work up the load again starting much lower with the mag primers. If you can get the same accuracy then it would be more economic. Or like mentioned change powders

[GUHunter]

Accuracy was very good with both standard and magnum primers (.6 - .7 MOA) and neither was significantly better in my limited exposure so far with the magnum primer loads. I tried magnum primers for 2 reasons (well 3, really). First is that ramshot magnum is a fine ball powder and better accuracy and consistent ignition are often associated with a magnum primer. Second was to see if I could safely squeeze a bit more out of the combo. The third is just that I can't help but tinker.

I wasn't using a chronograph (but I do have one) but my "shoulder gauge" said the recoil was noticeably harsher with the magnum primer. Perhaps I just need to break and the chrono and see where I'm at