Originally Posted by devildoc
I however don't think that the CCI primers not showing pressure signs is a good thing. They're just harder and don't show it, doesn't mean the pressure isn't there. I much prefer the federal primers for that reason, I can tell when I'm pushing max pressure when my primers start to flatten a bit, with the CCI's you might see extractor flow at almost the same time as those hard things start showin' you anything.
I have always found that the CCI primer showed pressure signs before the extractor marks showed up.
With the common practise of removing any slop in the action lockup, 'safe' chamber pressures have increased. I am not saying a huge increse, but definitely to the magnum+ range. Many of todays powders burn their best at magnum or slightly higher pressures. Low velocity variations and greatly reduced stringing are usually the benefits.
That provides a huge benefit in giving us accurate ammo for LR hits.
The CCI primer will not let get you to the point of locking up or grenading your action, but it will allow for a few more PSI's before flattening out when compared to the Fed.
Why is reducing runout important? Imagine that the bullet is 'crocked' as viewed down the bore. That bullet now engraves in the lands with the point off center. As it spins and leaves the barrel, it will fly wobbly like a poorly thrown football - each end wobbling around the path of flight. Pin point accuracy isn't going to happen.
The closer you can get that bullet centered on the rifling the more true the bullet will spin as it leaves. This reduces dispersion/inaccuracy at distance.