Question and a suggestion:
First the question: whose 6 1/2 primers are you using? Winchester only shows a single 6 1/2 small rifle primer, which they say is suitable for all their recipes spec'ing that size, apparently including .223/5.56 apps. Remington warns against using their "standard" 6 1/2 small rifle primer w/ .223/5.56 and certain other higher pressure cartridges. They tells us to use the 7 1/2 BR (same size) for those apps. I dunno about other brands and their recommendations, but their websites probably offer some suggestions. You may find a "dedicated" 5.56/.223 primer from some of them.
Problem seems to be leakage and/or pierced primers w/ possible damage to the bolt face from "gas cutting" which is a bit of a misnomer: it's not so much the hot gas as the high speed particles it carries that damages the metal (think sandblasting.)
Some folks claim they've ruined bolts, others that they've damaged 'em in as few as a dozen or so rounds, while there are those who claim they've loaded for years and years w/ a 6 1/2 primer, but often fail to give us the brand! So you've gotta do some research there... for my own use, Winchester fills the bill for almost all my uses, but that's a YMMV thing.
Now for a suggestion: Hodgdon's done a lot of the work for us. Go to http://www.hodgdon.com
, get into their reloading guide section, and you can tell it what caliber you want, which gets all the many recipes up on screen, or you can filter 'em out by bullet weight and/or powder. When you find a recipe you want to try, they'll generally give a starting load along w/ the maximum load. Looks like you can get a couple of recipes at the starting level which are "close enough" to that pressure level you'd mentioned. Hodgdon's doesn't seem to say anything about primers out front, but you should always dig around such websites for cautions. When in doubt, drop a note to the mfr: they're usually pretty good about answering questions, especially if a safety issue's at hand.
Good luck, and keep 'em at the low end of the "start low, work up" dictum, and you should find something that works ok for you. At first, you might want to load just 10 or so, then fire 'em single shot style, and examine each case for evidence of primer damage or leakage around the primer, take a look at your bolt face for evidence of hot gases hitting it, and decide from there whether to continue...