If you're going to try a flat-wire spring, maybe you should get one from the guy who (I think) invented the idea. David Tubb. He no doubt has done the most testing with them. This spring works in both Rifle and Carbine buffer systems, and it fits properly on both style buffers:
https://www.davidtubb.com/ar15-bufferspring
Having said that though, I'll admit I used one for a while but I found that it wouldn't allow some of my lighter loaded .223 ammo to cycle fully. So it made the most sense just to swap back to a standard spring. Might have been when I had it in my Rifle lower with the rifle buffer.
Haven't tried this spring with any of my Grendels, so I can't say how it works there.
ETA: After thinking about it, in this situation it might simply be best to start out running the rifle with a standard carbine spring and standard carbine (no "H" anything) buffer. See if it runs okay, meaning reliably, with that before experimenting with 'better' parts that might affect felt recoil, etc. it should work fine with standard parts. I believe Klem touched on this earlier. Make sure the rifle works with standard parts. Then maybe start playing with heavier buffers if you want.
https://www.davidtubb.com/ar15-bufferspring
Having said that though, I'll admit I used one for a while but I found that it wouldn't allow some of my lighter loaded .223 ammo to cycle fully. So it made the most sense just to swap back to a standard spring. Might have been when I had it in my Rifle lower with the rifle buffer.
Haven't tried this spring with any of my Grendels, so I can't say how it works there.
ETA: After thinking about it, in this situation it might simply be best to start out running the rifle with a standard carbine spring and standard carbine (no "H" anything) buffer. See if it runs okay, meaning reliably, with that before experimenting with 'better' parts that might affect felt recoil, etc. it should work fine with standard parts. I believe Klem touched on this earlier. Make sure the rifle works with standard parts. Then maybe start playing with heavier buffers if you want.