Primer:Powder compatability

[klink1983]

To clarify, I am new to reloading and value my eyesight and fingers, so I ask a potentially humerous question to experienced reloaders.

I'm learning more and more about the different types of powders, primers, load data etc. and the great attention to detail required....I also am feeling the addiction already, last night I only intended to fully prep 50 or so pieces of brass and that wasn't the case either. I kept on full length sizing, measuring, trimming, chamfering....before you know it, it was well after 3am this morning. I digress......

I have some Win748 (ball), as well as various granular powders; IMR4895, VV N150, Varget.

Yesterday I read that magnum primers should only be used with ball powder because they don't burn as fast as granular. A friend of mine who is well versed in reloading had mentioned that magnum primers are good to go with granular, provided I make the appropriate adjustment to my recipe by reducing my charge by .5 - 1gr to start.

Am I right or am I wrong? (Advice and funny stories are equally valuable)

 

[kayaker1]

In short: yes you can.
Mag primers are normally used when:

1) The published data calls for a mag primer (this should be the disclaimer)
2) Ball powders
3) Slow burning powders (e.g. RE22, RE25, Retumbo, IMR7828 etc)
4) Extreme cold

Some people used mag primers for all their loads. Using a mag primer can have a significant effect on pressure in some case/powder/charge combinations so the normal advice stands – if you use a mag primer in a load that calls for a standard primer reduce the charge and work back looking for pressure signs. On the other hand there are professionally measured tests you can find online where switching to a mag primer in certain cartridge/powder/charge combinations had an insignificant effect on pressure and velocity.

Sometimes a mag primer may improve accuracy, other times it may degrade accuracy. With a non-crimped bullet for example the extra primer force MAY jump the bullet forward a little before case pressure builds which can provide inconsistent start pressures. In other cases it may provide better ignition and more consistency. Typically, unless you are using ball powder there is little benefit to using a mag primer in smaller case capacity cartridges when using faster burning powders in cartridges like.308, .223 etc. Some do though and have good success.

On the flip side some reloaders use standard primers in larger capacity cases with 60gr+ charges and report excellent results.
The only way to know is to try and see how it works. As I said, if you change an existing load from standard to mag primer then reduce the charge. The 0.5-1gr equivalent is a rule of thumb, not an absolute.

I have used mag primers quite frequently in .30-06 and 6.5x55. I recently changed a 6.5 load from standard to mag primers (CCI200 – CCI250’s) and the average velocity increased by 50fps and accuracy improved (130gr Matrix FB, 47.5gr RE22). My reason was that RE22 has been known to be more difficult to ignite when very cold and I want to make sure of ignition for hunting loads.