Popularity of the 12.5" carbine-gas SBR?

[Rayrevolver]

40% is the increase from 10.5" to 11.5" per Paul from BCM. Not sure that same number applies 11.5 to 12.5.

I did the math a while back based on the a 20" rifle, M193. 10.5 to 11.5 is 33% increase. 11.5 to 12.5 is 24%. 10.5 to 12.5 is a 65% increase in dwell.

Baseline (20" Rifle aka 20R)
20.0" 0.184ms

Mid Length Gas
11.5” 0.053ms 71% less dwell time (or 29% of the dwell time of the baseline)
12.5” 0.079ms 57% less dwell time
14.5” 0.139ms 25% less dwell time
16.0” 0.181ms 2% less dwell time

Carbine Gas
10.5” 0.090ms 51% less dwell time
11.5” 0.120ms 35% less dwell time
12.5” 0.149ms 19% less dwell time
14.5” 0.206ms 12% MORE dwell time
16.0” 0.248ms 35% MORE dwell time