Rg1,
When Charles Petty did his 2006 Handloader article comparing primers, the Remington 7½BR was the hottest one he tested. He ran a .223 load of 24 grains of Reloader 10X under 55 grain V-max bullets, IIRC, and it gave him 3300 fps, as compared to 3150 using Federal 205 primers at the low end. So, for all practical purposes, that is a magnum primer.
mohr308,
The CCI #41 is a magnum primer, also. Identical to a CCI 450 except the height of the anvil feet is shortened to provide the lower military sensitivity spec for slamfire resistance in floating firing pin designs like the AR.
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Originally Posted by Slamedsi
If im only loading the minamal charge of 24gr can I get away with not loading a magnum primer?
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Actually the minimum charge is when you are most likely to need a magnum primer. Part of its function is to make more gas than a standard primer. That is needed to provide adequate start pressure in a large magnum case, but it can also be useful for improving velocity SD in non-magnum cases when the powder charge is low, leaving you with more empty air space to pressurize than normal.
The use of magnum primers with H335, BL-C(2), H380 and other Hodgdon spherical propellants started with CCI. In 1989, CCI reformulated their magnum primer flame temperatures and duration specifically for those former military powders (WC844, WC846 and WC852 in their military bulk versions). This was helpful because those powder's deterrent coating chemistry needs the boost for most consistent ignition. That said, the added velocity consistency won't normally show up on paper at 100 yards unless you have a rig that throws groups into the low 1's consistently. It is at beyond 300 yards that there starts to be enough vertical stringing from velocity spread that you might be able to tell.
These days, you also have the alternative of using Ramshot TAC or some other modern spherical powder with a more modern deterrent chemistry. I had a talk with one of Western Powder's lab techs, and he told me they'd eliminated the ignition issues with that line so that CCI's magnum primers were truly not required with it.
You might want to read
this article on primers.