May I use my available magnum large rifle primers with the the 500 S&W cartridge? I am aware that the magnum primer may increase chamber pressure. Will be loading 300 grain Hornady pointed bullets to about 1400-1500 fps.

Yes, you can use them without any problem.

Drop your load by 1 grain of powder and check for pressure signs. Then work back up to your normal load. You should have no problems.