Non magnum primer with a 7 PRC

Philward said:

It's interesting that I was just looking over some Speer load data for 257 Roberts and whenever they used ball powder, AA2700, W760, H380 & 414, they specified CCI250 primers with charge weights of only 40-45g. I have some 100g bullets loaded with 2700 and standard LR primers(Rem9.5 and CCI200) and will see how they work. Should be fine.

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I've read the same thing with using a mag primer with ball powders. It's always interesting to hear what results guys get. I tend to overthink reloading so I like to see what other fellas have experienced.

Anyone have any updates on what they have found between LR and LRM?

171farm said:

Anyone have any updates on what they have found between LR and LRM?

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The last bunch I loaded I used CCI34 and had a velocity spread of 6fps

victor3ranger said:

The last bunch I loaded I used CCI34 and had a velocity spread of 6fps

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I use LR primers in 7PRC with 70.2 grains StaBall HD and 168g LRX: shoots great and 2900fps.
I have tried mag pro, 4831, and 7828, all with LR primers.
I loaded both LRM and LR with the initial loads I tested to see differences in speed etc. with little appreciable differences. In at least one case, my SD and ES were better with the LR over the LRM primer.

Brad Quarnberg said:

I use LR primers in 7PRC with 70.2 grains StaBall HD and 168g LRX: shoots great and 2900fps.
I have tried mag pro, 4831, and 7828, all with LR primers.
I loaded both LRM and LR with the initial loads I tested to see differences in speed etc. with little appreciable differences. In at least one case, my SD and ES were better with the LR over the LRM primer.

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I actually just did the exact same thing last weekend. I used Staball HD with 168 gr LRX. I loaded 2 10 rd ladders, one with LR and one with LRM. I started at 67.3 and ended at 70 grains. The magnum started faster but around 69 grains, the velocities were starting to mirror each other. At 70 grains the MV was nearly identical (2861 and 2826).

I noticed some erratic jumps in velocity with the LRM Ladder. The LR was much more consistent and had defined nodes throughout. Granted, it's one rifle, one test, but I thought it was interesting.

I'm going to work up to max charge and do the same experiment later this month.

I used Fed 210 in my 7/300 weatherby for match with H1000

Consistency of LR primer over LRM is a known thing. Google it.

LRM in "magnum" is NOT required for consistent ignition. However, low temperatures can cause problems, usually in hunting situations, and it's chemistry I do not understand so I can't explain other than it does happen.

It is the same idea as SR primers in the 308 Winchester and "smaller" chamberings. SR in 6mm BR derivatives, Creedmoor derivatives, 260 and 243 all work and depending on the reloader and rifle, have lower SD and dispersion. Not always, not a perfect world.

If you experiment with LR in "magnum" cases and experience lower SD and dispersion, go for it.