12-02-2023, 07:02 PM
Welcome aboard Tango. First thing to be aware of, is the 6mm ARC and the 6.5 Grendel do not show brass marks until way over-pressure, since they are (for ARs) 52000 psi Saami limit rounds.
So you can't go by the old standby of if there are no marks, then I'm not over-pressure.
As to RL 15.5, I'm in a wait and see, RL15 and Varget are both listed in Hornady data but you don't get a lot of MV for the heavier bullets. I've got some loads that are ok for 100 gr in Varget, but in general those are for bolt action where the Saami is 62Ksi -- not that I have to go 'way up close to that.
Burn rate does not tell the whole story when it comes to Lever and CFE, those 2 powders have a markedly different, and more rounded, pressure curve than other powders, which is why, peak psi to peak psi, you get more MV out of them (MV is proportional to the area under the Pressure curve, not, strictly speaking, to the peak itself).
Now 15.5 may have that same rounded psi characteristic as CFE/Lvr, but I have not seen this documented or discussed anywhere. So, wait and see. OTOH, for Grendel several of us have found that AR Comp, which is not a documented powder, works very well for the 120 class 6.5 bullets in the Grrr... so 15.5 may indeed turn out to be that kind of powder for the Arc.
The other useful tool(s) are Quickload or Grt, but again, for the short cartridges like Grendel/ARC, these 2 apps need some tuning to be truly representative... there are lots of discussions on 65Grendel.com about this by guys who were in on some of the first testing, I myself have found it to be true for Grt, but have not devoted the time/effort to QL. So it can be useful but according to those guys, they take more tweaking than most cartridges.
The mostly go-to powders for the Arc are pretty much the ball powders like Lvr and CFE, with AA2520 right in there. I've seen some drop in MV per temperature, from CFE and Lvr but not to the extent that "charts" say they should... 'course I'm new to that MV-temp measuring game, so I can't draw conclusions on them one way or the other.
Anyway, will be interested on what y'all find out about 15.5 in the Arc, we're always open to learn something!
So you can't go by the old standby of if there are no marks, then I'm not over-pressure.
As to RL 15.5, I'm in a wait and see, RL15 and Varget are both listed in Hornady data but you don't get a lot of MV for the heavier bullets. I've got some loads that are ok for 100 gr in Varget, but in general those are for bolt action where the Saami is 62Ksi -- not that I have to go 'way up close to that.
Burn rate does not tell the whole story when it comes to Lever and CFE, those 2 powders have a markedly different, and more rounded, pressure curve than other powders, which is why, peak psi to peak psi, you get more MV out of them (MV is proportional to the area under the Pressure curve, not, strictly speaking, to the peak itself).
Now 15.5 may have that same rounded psi characteristic as CFE/Lvr, but I have not seen this documented or discussed anywhere. So, wait and see. OTOH, for Grendel several of us have found that AR Comp, which is not a documented powder, works very well for the 120 class 6.5 bullets in the Grrr... so 15.5 may indeed turn out to be that kind of powder for the Arc.
The other useful tool(s) are Quickload or Grt, but again, for the short cartridges like Grendel/ARC, these 2 apps need some tuning to be truly representative... there are lots of discussions on 65Grendel.com about this by guys who were in on some of the first testing, I myself have found it to be true for Grt, but have not devoted the time/effort to QL. So it can be useful but according to those guys, they take more tweaking than most cartridges.
The mostly go-to powders for the Arc are pretty much the ball powders like Lvr and CFE, with AA2520 right in there. I've seen some drop in MV per temperature, from CFE and Lvr but not to the extent that "charts" say they should... 'course I'm new to that MV-temp measuring game, so I can't draw conclusions on them one way or the other.
Anyway, will be interested on what y'all find out about 15.5 in the Arc, we're always open to learn something!