i reload for a guy i work with 7MM and 270 and and 300 win mag all with reloader 22 the 300 mag calls for mag primers he bought a case of cci mag primers and wonts to us them in all of these he said that the mag primers wont change the load that much i have never used a mag primer in a none mag load what do you think

In rifles I always used standard or magnum primers depending on what the manual suggested. The large Magnum case full of slow burning powder does indeed benefit from the hotter primer. In the non magnum rifle calibers I used standard rifle primers. Years ago a local gunsmith/retailer/shooter told me that handguns didn't need the magnum primer. Never have used magnums in handguns EXCEPT for the really big stuff: 454, 460, 500(no, I don't shoot these wrist wrenchers myself; I have loaded for a friend before he got set up to make his own!). Personally, if I wanted to experiment I'd do it with my own ammo and tell my friend that as a matter of saftey/liability you intend to follow the load manual advice.

We've been loading my dad's 7mm Mag for 44 years with 68.0 gr of IMR 4350 and a Remington 9 1/2 (not a 9 1/2M) with a 139-140 gr bullet. It clocks right at 3200 fps with 40 year old R-P or Norma brass.

It shoots around 1 MOA and part of that is probably due to the case being fuller than when a magnum primer is used. The current loading data is around 65.0 gr of IMR 4350 with a magnum primer. I need to check the groups with the newer Canadian IMR 4350, since it has shorter tubes and doesn't fill the case as well.

Speer #14 does not use mag primers with any .270/RL 22 loads; however, RL 22 in 7mm mag and .300WinMag get the mag primers.

Bob

You can't just change the primer, you have to re-work the powder load from the starting amount when changing from standard to magnum primers (or magnum to standard). A magnum primers greater fire can cause better powder ignition, which can raise the pressure level of the load as it finishes burning faster than before. The volume for the gases released by the burning powder isn't as great as the bullet hasn't had as much time to move, so you end up with more pressure from the same amount of powder.
So start low, and watch for pressure signs, and stop when you get to a load that delivers the accuracy you are looking for; or you notice pressure signs or reach the max load in the manual.

Mag primers can account for AS much as 1 gr. of powder, if it calls for it then use it but if not then follow load guide lines.Seems to work for me