You posted in the MG section but your post eludes to being related to the M16 right? I post all the time about cyclic rates and smoothing out the M16 in various calibers.
Below is what I would consider a 'baseline' milspec MK18 configuration.
I don't think it is particularly smooth though. I do a ton of testing to smooth things out and slow the cyclic rate down.
Below is the same exact upper and the only change is a Tubb 556 flat spring and a Kynshot hyrdaulic RB5005 4.7 oz buffer which is almost identical in weight to the H2 buffer and yet I get 138 RPM slower cyclic rate using these two components.
I personally do not like just throwing mass at the problem as it can make the gun bouncy. I try to reduce the amount of reciprocating mass to an extent.
Please check out these links on my site:
https://c3junkie.com/?page_id=977 (this links discusses the use of the Tubb flat spring and then hydraulic buffer)
https://c3junkie.com/?page_id=1403 (my M16 'Ultimax' project where I get the M16 to achieve constant recoil and the BCG does NOT bottom out on the bottom of the buffer tube)
My main AR15/M16 page with other links you may find helpful and buffer data:
https://c3junkie.com/?page_id=164