05-03-2022, 04:02 PM
You're fine. Yes, that COAL is a bit low, but I find Grendel chambers to often be quite short throated, so am not surprised. In general rifle compressed COAL isn't a big deal like pistol round COAL is. Rifle powder is slower burning and the reaction chamber volume is much larger. The relative decrease in initial reaction chamber volume compared to a pistol casing of .1" COAL shorter, is much lower by percentage. And peak pressure in a rifle doesn't usually hit until about 2" or so of travel, unlike a pistol which hits it darned near right away at about 0.1" even, by some analysis at least.
Point being, you will be safer running COAL, than you will being in the lands, which does give a pressure spike, since the bullet can't start moving to decrease pressure any at all, until there's already enough force under it to start deforming it into the lands. Gunpowder burns in a bootstrap fashion, where the higher pressure the faster it burns the higher the pressure. In too short COAL, a rifle will start pushing the bullet forward and increasing the reaction chamber size (and thus decreasing gas pressure growth rate) relatively easily and at lower P.
Also, 25 gr of ARComp isn't an excessive charge. I run 26 gr under 123 bullets, though will admit that might be overly strong.
Point being, you will be safer running COAL, than you will being in the lands, which does give a pressure spike, since the bullet can't start moving to decrease pressure any at all, until there's already enough force under it to start deforming it into the lands. Gunpowder burns in a bootstrap fashion, where the higher pressure the faster it burns the higher the pressure. In too short COAL, a rifle will start pushing the bullet forward and increasing the reaction chamber size (and thus decreasing gas pressure growth rate) relatively easily and at lower P.
Also, 25 gr of ARComp isn't an excessive charge. I run 26 gr under 123 bullets, though will admit that might be overly strong.