I'm just getting acquainted with Gorden's Reloading Tool (GRT). You might like to get a free download and explore what it has to offer. My beginner results from GRT puts a Grendel with IMR 4895 with 129 abler (len=1.350) with a case OAL of 2.280 max before warnings = 26.6 for a velocity of 2141 from a 12.5 barrel. (52782 p.s.i.). Disclaimer: The tool is just an estimate, I'm not advocating going past published load data, don't try at home etc....
There was one warning: low burn rate, inconsistent combustion, and increased error rate of the simulation very likely.
There was one warning: low burn rate, inconsistent combustion, and increased error rate of the simulation very likely.