G-manz35, back in the day, I used to develop loads incrementally, and used manuals as a "guide." I thought nothing of using a Powley computer for a start point, maybe interpolate between bullet weights or powder burn rates, you know, 'safely'. In my time, frankly, all the gun-writers did the same, carefully explaining the signs they were looking for, the careful measurements of case-head expansion, delta velocity versus delta charge, primer shape, force to re-size, difficulty with bolt lift, while they sought the fastest, hottest load they could wrinkle out of a new gun, or with a new powder, or whatever. Velocity was truly god.
Then, a couple of ballistic labs started accepting private jobs, wherein a client specified case, primer powder charge, bullet, and, if they thought they could safely shoot it in a calibrated pressure barrel, then, for a few hundred bucks, (calibration is pricey) they would pop enough of the client's caps that they could establish a reliable set of numbers.
Oops. All of a sudden, the gun writers mostly got religion. Those loads that met, exceeded, or just plain blew away factory "specs" very frequently were running 10, 20 thousand psi over SAMMI specs. That's OK for proof loads, but over time, a gun shooting over-pressure loads, but the cases exhibiting no signs of excess pressure, well, the gun just wears out faster.
Oh, there are still a few of the old breed, writing about how they can wring a few extra fps out safely, but with loads they have not taken to a credible lab, but the most of them acknowledge that when they get to book max, they are at SAMMI spec max. Especially, those guys who used to be manufacturer ballisticians.
Me, now, if a load is max in a recent book, I gotta have a very good reason to drop it into a case. Ammo specs on the box are generally a bit closer to true these days, 'cause everyone has a chrono. I guess i kinda rant every time I see someone suggesting that the means available to a hand loader to ascertain his loads are safe - unless they are within book values - when history has shown that such assessments can be so far out as to be actually dangerous. Lots on here disagree, though, and it is a tribute to the engineering of modern firearms that we have so few catastrophic failures.