skahunter831
FNG
- Joined
- Jan 5, 2023
- Messages
- 29
Hi all, I got Gordon's Reloading Tool a little bit ago and really love using it. It's made me much more aware of what factors affect pressures, velocities, etc. I've been working on a 7mm RM load with Nosler AB 160s, using H1000 powder. I bought a box of Norma brass, and have a fair amount of Nosler brass as well. When I wasn't quite getting velocities I expected with around 69 grains of H1000, averaging 2,850 fps, I decided to measure case capacity. Lo and behold, the Norma brass has a capacity of 87 grains h2o, and the Nosler 85 grains, both well above the SAAMI spec of 82 grains. And as I've learned, that case capacity can dramatically affect pressures and speeds.
Using GRT, the SAAMI spec case capacity, and my COAL of 3.365" (70 thousands off lands, which seems to fit my rifle), my 69.1 grain charge was expected to produce pressures of 57,440 psi and velocities of 3,011 FPS (in my 24.3" tikka barrel). If I adjust case capacity to the Norma 87 grains, pressure drops to 49,524 psi and velocity to 2,900 FPS. My measured shots averaged 2,850 (plus or minus ~15-20 FPS, haven't calculated any more statistics than that).
So then I noticed the "initial pressure" input in GRT. As seems clear, they intend this factor to be a calibration for measured performance. The default for rifle, jacketed bullet, and magnum primers (I'm using CCI LR mags) is 5,221. In order to match my measured velocity (2,850) to the modeled, I have to reduce the initial pressure to 3,400, which brings total max pressure down to 46,910.
Am I using GRT correctly? Or missing anything?
Given all of the above, I could put over 74.5 grains of H1000 in the case before reaching max pressure, which would bring my velocity over 3,110 fps. I'm not chasing speed just for speed's sake, in fact this load brought down a raghorn bull quite quickly at 75 yards last week and it might have been a lot messier with 150 fps higher velocity. I also don't want to burn out the barrel or throat by pushing it. But in general I would like to be getting closer to 3,000 fps and get the easily-achievable performance out of the rifle and load.
My plan is to to more charge weight testing, starting around 72 grain in 0.5 grain increments, up to 74 just to see what I see. Any other thoughts or advice? Thanks!
Using GRT, the SAAMI spec case capacity, and my COAL of 3.365" (70 thousands off lands, which seems to fit my rifle), my 69.1 grain charge was expected to produce pressures of 57,440 psi and velocities of 3,011 FPS (in my 24.3" tikka barrel). If I adjust case capacity to the Norma 87 grains, pressure drops to 49,524 psi and velocity to 2,900 FPS. My measured shots averaged 2,850 (plus or minus ~15-20 FPS, haven't calculated any more statistics than that).
So then I noticed the "initial pressure" input in GRT. As seems clear, they intend this factor to be a calibration for measured performance. The default for rifle, jacketed bullet, and magnum primers (I'm using CCI LR mags) is 5,221. In order to match my measured velocity (2,850) to the modeled, I have to reduce the initial pressure to 3,400, which brings total max pressure down to 46,910.
Am I using GRT correctly? Or missing anything?
Given all of the above, I could put over 74.5 grains of H1000 in the case before reaching max pressure, which would bring my velocity over 3,110 fps. I'm not chasing speed just for speed's sake, in fact this load brought down a raghorn bull quite quickly at 75 yards last week and it might have been a lot messier with 150 fps higher velocity. I also don't want to burn out the barrel or throat by pushing it. But in general I would like to be getting closer to 3,000 fps and get the easily-achievable performance out of the rifle and load.
My plan is to to more charge weight testing, starting around 72 grain in 0.5 grain increments, up to 74 just to see what I see. Any other thoughts or advice? Thanks!
