Peterson has introduced a series of LONG brass for competitive use that can be trimmed to meet the shooters needs to customize to an individual firearm.

I am trying to figure out if there is an advantage to use this brass in a semi-auto AR based rifle.  I don't see the advantage since I'm not loading to touch (or nearly touch) the lands  with the bullet ogive.  Is there an advantage in case life to load with a longer brass case?  I'm a long time reloader (50+ yrs), but have never loaded for a belted magnum round that doesn't  headspace on the bottleneck or measured at the datum before. On this one, I'm back to being a noob.

Thanks in advance.

The little I know about this -

Peterson brass is very decent quality, overall.

I had to neck turn every single piece of brass because the case necks were way too thick to even seat a bullet in my die.  This is not a problem but is an unexpected nuisance for otherwise premium brass.  If I did not have a neck turning set up, I might feel otherwise and less kindly.

After that first firing, I thought reloaders of belted magnums would re-size the cases to headspace off the shoulders (like all other bottle neck cartridges).  That is, if the usual 2-3 mil set back of the shoulder still allows the brass to chamber.  As I understand it, headspace relative to the belt can be large (sloppy) leading to shortened case life.

That's all I know and half of it is hear say (from credible people).  

Good luck!