Standard and +P brass is the same. Brass isn't strong enough to withstand the pressures of any cartridge, all you need to see is a round that's gone off before chambering. The steel chamber contains the pressure, the brass holds the charge and the bullet and acts as a 'gasket" in the chamber so don't think selection of a case is going to allow you to load at higher pressures safely.
It is a mistake to think that pressure is the only factor in bullet velocity. The powder burn rate and how the pressure is released over time is more significant than simply the amount of peak pressure generated.
If you want to duplicate commercial and LEO +p and +P+ velocities then that can generally be done by proper selection powder type and charge generally without exceeding peak standard SAAMI pressure.
A good example of this is the Federal 9PPLE load that is a +P+ rated 115gr round. Advertised by Federal/ATK this round sends the bullet out the muzzle of a 4" barrel at 1,300 fps at the muzzle. Real life measurements are often a bit less and from a Glock 19 most report 1,230 to 1,250 fps. The lower velocity could be attributed to different temperature and elevations and distance to the chronograph. Regardless the numbers are what they are.
Using Remingotn 115gr bulk bullets I've loaded behind 6.0 grs of Unique I get an average velocity of 1,257 fps and current data states that max load for 115gr JHP is 6.3grs with a "book" velocity of 1,300 fps at pressures less than SAAMI standard maximum for the same velocity as Federals +P+.
I know people love to brag about loading the +P, +P+ or extra velocity but don't fall in love with the +P or +P+ label. Its the speed at which the bullet leaves the muzzle that counts and how much peak pressure the cartridge produces isn't the most important factor in getting that velocity. Remember too that you can reduce the effectiveness of a good bullet by pushing it beyond its optimum velocity. High velocity doesn't guarantee better performance.
