9mm AR15 / M16 Ported SD vs non-ported

Someone gave me a straight blowback SD upper a long time ago.  I have always reloaded 9mm 147Gr for all my 9mm guns so I didn’t have to keep different rounds for suppressed vs non-suppressed.  I recently decided to re-core the old SD can.  Mainly because it was straight blowback and I wanted to go with the CMMG RDB system.  I started off with a stainless 5″ Odin Works that I modified for the CMMG RDB system and then gradually drilled ports till 115Gr Federal Blazer went subsonic.  I stopped at 6 ports.  During this process, I also happened to have a 4.5″ stainless barrel from another blank supplier that I chronographed out of curiosity.  To my surprise, it was already subsonic.  I do see that Ballistics by the Inch only lists two different 115Gr loads but they are hot self defense loads: http://www.ballisticsbytheinch.com/9luger.html  I don’t see any testing for ‘cheap’ 115Gr ball ammo. 

Here are some chronograph results with the 4.5″ stainless barrel above, left.  Notice how slow the 124Gr Aguila is.  All data below was with the Octane9 suppressor mounted.

115Gr Blazer 124Gr Blazer
124Gr Aguila
 115Gr 4.2Gr Bullseye
1050 1051 986 1005
1055 1063 993 1007
1022 1047 944 1020
1059 1068 967 977
1066 1053 1006 964
1050.4 Avg 1056.4 Avg 979.2 Avg 994.6 Avg

Thinking this may have been a fluke, I got a second 4.5″ barrel from a different blank manufacturer (Green Mountain).  I tested using the same lot of 115Gr Blazer.  This time, higher velocities than the first barrel but here in Florida, it is still barely subsonic.  Probably not subsonic in northern states or higher altitudes.  https://www.weather.gov/epz/wxcalc_speedofsound
According to the link above, 80 Degree’s F the speed of sound is 1138.52
Data below is also with Octane9 mounted.

115Gr Fed Blazer
 124Gr Blazer
115Gr 4.2 Bullseye
 124Gr 4.2 Bullseye

  124Gr 3.7 Titegroup
1094 1105 1077 997 935
1117 1091 1062 1016 918
1072 1059 1076 1028 953
1106 1103 1043 993 949
1134 1088 1024 1017 946
1104.6 Avg 1089.2 Avg 1056.4 Avg 1010.2 Avg 940.2 Avg

Pictured below is the 4.5″ 3 lugged barrel and it is super short and very lightweight.  Going with a non-ported allows you to quickly change to different suppressors with varying levels of performance and backpressure.  While there are several SD cans out there, they are all designed for a specific barrel and will most likely be longer than below.

An argument could be made that the SD has better weight distribution being less front heavy but in the picture above, that setup is super light and not front heavy at all.

A ported setup ‘may’ be softer shooting but I cannot tell a difference at this time.