I am developing loads in 300 RUM and noticed that many of the loads posted on the accurate reloading website for this caliber far exceed loading manual maximums. I realize that the manuals cover the mfrs butts, but in 180 Barnes X, most of the loads on the website are way high. I am shooting a Rem Sendero w/ stainless fluted 26" bbl, just like the one they used to test the loads they posted, and I am wondering how safe those high end loads were. What pressures etc.?
Any help on this would be appreciated.

Bullet weights and makes please!

Bullets = Barnes 180gr XBT, and also Scirroco 180gr.

According to Barnes Manual below is recommended. But I locked up a piece of brass in my RUM going above 87gr of Re22 with 180gr X. Not all guns can do that. And shocked they were able too. Even with 180gr triple X's, I wasn't able to go over 91gr of Re25 without some serious primer flattening. I do have a krieger barrel, and it seems to build pressure a tad faster than my factory barrels. As always, (especially with Barnes, TBBC, and failsafes), start at the bottom and work your way up.

300 Rem Ultra Mag

180grn XFB/XBT
H1000
starting load 86grns - 3047fps
max 91grns - 3224fps

RL22
starting 79grns - 3136fps
max 84grns - 3334fps

RL25
starting 84grns - 3170fps
max 89grns 3359fps

I was able to go to the max RL25 load in the Hornady manual which clocked 3400fps ave from my 700SS without pressure problems with the Barnes 180 XBT, but just remember, guns, like shooters are individuals and an extra 50fps is not worth stressing about.