Smoothness:
Mp5 & clones..in most cases.
Sig Mpx gas can be good.
CMMG radial delayed .. tuned
Stribog A3 delayed blowback
Kuna same.
Most direct blowbacks jump around like a Mexican jumping bean unless they are heavy.
Now this is a matter of perspective and some people will not think the direct blowback is that bad..others will hate it.
FRT, binary and SuperSafeties will magnify this.
Mp5 & clones..in most cases.
Sig Mpx gas can be good.
CMMG radial delayed .. tuned
Stribog A3 delayed blowback
Kuna same.
Most direct blowbacks jump around like a Mexican jumping bean unless they are heavy.
Now this is a matter of perspective and some people will not think the direct blowback is that bad..others will hate it.
FRT, binary and SuperSafeties will magnify this.

