11-23-2024, 09:03 PM
I, too, own and shoot both the grendel and 6 Arc, the Grrr for 8+ yrs and love the 8208 powder for 120 class. I save my 8208 for the grendel.
The powder-pressure response for the 6Arc is different than the grendel: with a smaller diameter bullet and barrel, pressure builds up more quickly and has smaller overall volume down the barrel. This is why 8208 is a kinda-fast powder type for the Arc.
6Arc typically needs slower powders for the similar weight bullet as compared to the 6.5 Grendel. You can push it too far in the 6 Arc.
The 6 Arc hornady data is for an 18" AR barrel, if you have a 20" then you will get about 75 fps more than the 18" listed.
You don't say what bullet you use in the grendel to get to 3000 ft/sec (6.5 does not have an 87 gr Vmax if I'm not mistaken), but in any case, you cannot simply extrapolate from grendel over to 6 Arc.
You also did not say what brand of 6.5 cases you are necking down. You are probably aware that one grendel case-mfr probably does not equal the volume in another mfr's case... so again, extrapolating straight over is not a good idea.
Best to start low and work up, noting for signs of overpressure - which liek grendel, if you have them you are already over 52 ksi limit. Stay within mfr data until you have a lot of experience and are willing to experiment a little. Both of these calibers achieve their results with moderate case pressures, they are not rifle-hot rods nor iron-clad magnums. Efficiency wins out over brute powder/force.
The powder-pressure response for the 6Arc is different than the grendel: with a smaller diameter bullet and barrel, pressure builds up more quickly and has smaller overall volume down the barrel. This is why 8208 is a kinda-fast powder type for the Arc.
6Arc typically needs slower powders for the similar weight bullet as compared to the 6.5 Grendel. You can push it too far in the 6 Arc.
The 6 Arc hornady data is for an 18" AR barrel, if you have a 20" then you will get about 75 fps more than the 18" listed.
You don't say what bullet you use in the grendel to get to 3000 ft/sec (6.5 does not have an 87 gr Vmax if I'm not mistaken), but in any case, you cannot simply extrapolate from grendel over to 6 Arc.
You also did not say what brand of 6.5 cases you are necking down. You are probably aware that one grendel case-mfr probably does not equal the volume in another mfr's case... so again, extrapolating straight over is not a good idea.
Best to start low and work up, noting for signs of overpressure - which liek grendel, if you have them you are already over 52 ksi limit. Stay within mfr data until you have a lot of experience and are willing to experiment a little. Both of these calibers achieve their results with moderate case pressures, they are not rifle-hot rods nor iron-clad magnums. Efficiency wins out over brute powder/force.