Back at the Grendel news... Stiffer recoil than the 5.56 stuff. Between 5.56, 300BLK and 25-45, they all feel the same. Well, for some reason, the 25-45 recoil feels a little bit less than regular 5.56. Weird. Anyway, the Grendel has more of a kick to it, but I still wouldn't call it anything near "heavy recoil..." No way... You can tell there's a difference, though.
Built the recoil system from the parts box - regular carbine buffer spring, mil-spec carbine receiver extension, and a standard-weight carbine buffer (3.0 oz). I figured that would be the first thing to change now, but instead of just going to a heavier carbine buffer, I picked up a VLTOR A5 recoil system. They have a receiver extension with either 6 positions or 7 positions - so I grabbed the 7 position. Did the A5 H1 buffer, which is 4.56oz - damn near the same as a carbine H2 buffer, which would be 4.7oz. Armalite M16 rifle spring. Probably won't get it out until next weekend, but we'll see what kind of difference it makes.
I've got some buffer options in the future, if I want to go heavier.
Weights for the A5 buffers
A5 H0: 3.80oz
A5 H1: 4.56oz
A5 H2: 5.33oz
A5 H3: 6.08oz
A5 H4: 6.83oz
Compared to these:
AR15 Carbine Buffer Weights
Carbine Buffer (Avg 3.0 oz)
Heavy (H) Buffer (Avg 3.8 oz)
H2 Buffer (Avg 4.7 oz)
H3 Buffer (Avg 5.6 oz)
Rifle Buffer (Avg 5.0 oz)