In the second part of this ongoing series detailing as many commercially available ultra-short (sub-7″).300 Blackout barrels as possible, I’m not only adding two more to the lineup, I was able to obtain more ammo to test last articles barrels with as well.  The two new barrels are both from KAK: the first is their venerable “Baby Blonde” 6.25″, the other is their brand-new 4.75″ (nickname in progress).   Some additional chrono data will be included here for the V Seven 6.5” and the Right To Bear 6” barrels tested in Part 1.  If you like time travel, jump to Part 3.

Due to the limited quantity of a couple ammo types, some of the chronograph data is somewhat limited.  I’d like to have multiple 5- or 10- shot strings for each ammo type through each barrel, but it wasn’t possible.  Likewise, accuracy testing should also be considered preliminary, as none of these barrels are totally broken in before grouping starts, I simply don’t have an extra hundred rounds per barrel.  I do get a good sense of how these function (while suppressed or unsuppressed), general velocity data and which ammo each barrel prefers.  This will allow me to pare down the ammo selection for a final accuracy review later.

So let’s talk tech specs on this article’s newcomers:

KAK 4.75″ with Micro Gas Tube and AR15 configurable buffer system, data from KAK.

  • Stainless Steel 416R
  • 1:7 Twist
  • 5R Rifling
  • Micro-gas length (1.5″ shorter than pistol length system)
  • .125″ gas port size
  • .750″ gas block journal
  • M4 feed ramps
  • 5/8×24 threaded muzzle
  • 10.48 ounces (barrel alone)
  • Special tuning might be required, this barrel requires a short barrel nut or modified grooved barrel nut to clear the micro gas tube (covered in installation below)
  • Price: Currently $200

Ultra-short .300 Blackout barrels round-up

KAK 6.25″ “Baby Blonde”

  • Stainless Steel 416R
  • 1:7 Twist
  • 5R Rifling
  • Pistol length gas system
  • .125″ gas port size
  • .750″ gas block journal
  • M4 feed ramps
  • 5/8×24 threaded muzzle
  • 13 ounces (barrel alone)
  • Price:Currently $199

Ultra-short .300 Blackout barrels round-up

Both of these barrels I assembled onto uppers.  Both used ALG Defense handguards, which had to be trimmed down by about 9″.  The 4.75″ barrel’s micro length gas system required I make some modifications to the barrel nut:  I cut it in half (the forward half provided support for the long handguard, which wasn’t there anymore) and notched out the barrel nut on top-dead-center.  I made sure there was enough material left on the nut to support the barrel.  The Baby Blonde was assigned the tan handguard and the 4.75″ the black handguard.

Both barrels received an AAC 51t suppressor mount for subsonic work, the Baby Blonde getting a three-pronged flash hider and the 4.75″ barrel getting a Breakout (mistimed 180°, I’m swapping mounts often so not too worried about it.  The barrels in Part 1 had mistimed muzzle devices as well, just hidden beneath a flash can or suppressor).

The day’s ammo selection

All firing was done from a Caldwell Stinger shooting rest at 50 yards for groups and through a Caldwell Ballistic Precision chronograph at the recommended 10-foot distance.  Both KAK uppers shared a 4x Trijicon ACOG with ACSS reticle.

9 different ammo types were tested, but that bears some discussion.  My on-hand supply of Barnes RangeAR was very limited, and I only had three rounds of Reaper Controlled Chaos.  I ran the Reaper round through the 4.75″ barrel, as data can be found for it from 6-7″ barrels.  Abbreviations for the two barrels will be, Baby Blonde (BB) and 4.75″ (475) and additional data for the barrels from Part 1, V7 6.5″ (V7) and Right To Bear 6″ (R2B).  Chrono data from Part 1 for V7 and R2B will be inserted here as well.


All rounds listed below cycled through both barrels with mil-spec BCG and standard weight buffer.  Last round locked the bolt back with each ammo, unsuppressed.

Barnes RangeAR 90gr:

  • 475 Average 1961 fps.  Standard deviation (SD) 21
  • BB Average 2080 fps, SD 51
  • V7:  Average 2166 fps, SD 37
  • R2B: Average 2104 fps, SD 19

Reaper Controlled Chaos 110gr:

  • 475 Average 1792 fps,  SD 31

Barnes Tac-TX 110gr:

  • 475 Average 1846 fps, SD 6
  • BB Average 1946 fps, SD 8
  • V7:  Average 1977 fps, SD 14
  • R2B:  Average 1923 fps, SD 8

Federal All-Copper 120gr:

  • 475 Average 1662 fps, SD 45
  • BB Average 1714 fps, SD 15
  • V7: Average 1794 fps, SD 8
  • R2B: Average 1735 fps, SD 8

ADI MSR 125gr Sierra Matchkings

  • 475 Average 1651 fps, SD 60
  • BB Average 1751 fps, SD 32
  • V7 Average 1775 fps, SD 20
  • R2B Average 1740 fps, SD 10

Ammo Inc Jesse James 150gr soft point

  • 475 Average 1613 fps, SD 18
  • BB Average 1661 fps, SD 10
  • V7 Average 1698 fps, SD 13
  • R2B Average 1642 fps, SD 14


Will indicate if the round cycled (CYC), or locked the bolt carrier on last round (LB) suppressed (SUP) or unsuppressed (UNSUP).

Ammo Inc /Stelth/ 220gr

  • 475 Average 863 fps, SD 22.  CYC and LB UNSUP and SUP.
  • BB Average 880 fps, SD 19.  CYC and LB UNSUP and SUP.
  • V7 Average 931 fps, SD 11.  CYC and LB UNSUP and SUP.
  • R2B Average 906 fps, SD 25.  CYC and LB SUP, CYC with no LB UNSUP.

Fiocchi 220gr subsonic

  • 475 Average 819 fps, SD 33. CYC and LB UNSUP and SUP.
  • BB Average 821 fps, SD 8.  No CYC or LB UNSUP, positive CYC and LB when SUP.
  • V7:  Average 810 fps, SD 14.  CYC and LB SUP, CYC but no LB UNSUP.
  • R2B: Average 835 fps, SD 9.  Did not CYC UNSUP, CYC AND LB while SUP.

Discreet Ballistics 190gr subsonic

  • 475 Average 831 fps, SD 23. CYC but 50% LB UNSUP, CYC and LB when SUP.  BCG was getting real dirty at this point.  Added lube.
  • BB Average 864 fps, SD 38. NO CYC or LB when UNSUP, positive CYC and LB when SUP.
  • V7 Average 904 fps, SD 19. CYC and LB SUP, CYC but no LB UNSUP.
  • R2B Average 870 fps, SD 27.  CYC and LB SUP, 50% CYC and 50% LB when UNSUP.

Remington 220gr subsonic round

  • 475 Average 889 fps, SD 8.  CYC and LB both SUP and UNSUP
  • BB- test data recorded on video, memory card ran out of memory.  Data lost.
  • V7 Average 930 fps, SD 38.  CYC and LB SUP, CYC but no LB UNSUP.
  • R2B Average 900 fps, SD 31.  CYC and LB when SUP, did not CYC or LB UNSUP.


I’ll mention it yet again that these accuracy results are preliminary, as all of the barrels I’ve received have been factory new.  Once broken in, groups usually shrink somewhere between “noticeably” and “significantly”.  Some of this can be seen in the (in)consistency of groups, where two groups from the same barrel with the same ammo will perform very differently not two minutes later.  I wanted to get some groups to see what ammo types each barrel preferred, to pare down the options later.  More exhaustive accuracy testing to come.  Accuracy results for V7 and R2B found in Part 1.  Unlike Part 1, called flyers were simply discarded.  Here’s results sorted by barrel.

KAK 4.75″

Barnes 110:  1.33″–2.54 MOA

Federal 120:  2.91″ &  7.5″–5.55  & 14.3 MOA

Ammo Inc JJ 150:  1.57″ & 1.8″–2.99 & 3.43 MOA

Discreet Ballistics 190:  1.88″–3.59 MOA (stabilized)

Ammo Inc /Stelth/ 220:  1.9″–3.62 MOA (slight yaw in bullets, no baffle strike)

Remington 220:  1.82″ & 1.64″–3.47 & 3.13 MOA (some rounds yawed slightly, most stabilized)

Fiocchi 220:  1.6″ & 2.05″–3.05 & 3.91 MOA  (stabilized)

KAK 6.25″

Barnes 110:  2.29″ & .99″–4.3 & 1.89 MOA

Federal 120:  1.6| & 1.98″– 3 & 3.78 MOA

Ammo Inc JJ 150:  .91″ & 2.1″–1.73 & 4 MOA

Discreet Ballistics 190:  1.92″ & 2.39″– 3.66 & 4.56 MOA (stabilized)

Ammo Inc /Stelth/ 220:  1.79″ & 3.4″–3.41 & 6.5 MOA (stabilized)

Remington 220:  1.11″–2.11 MOA (stabilized)

Fiocchi 220:  1.03″ & 2.22″–1.96 & 4.23 MOA (stabilized)


There’s the raw data so far, take it as you may.  A couple observations:  The KAK 4.75″ barrel is right on the edge of usable length.  The lighter supersonic rounds had an immense concussive effect and blew the charging handle back with each round.  A linear compensator/blast can is a necessity.  The lighter subsonic round by Discreet Ballistics stabilized just fine and looks to be a good fit with this tiny barrel.  For those saying such a barrel is essentially a pistol caliber carbine, the 90gr bullet was moving at ~1961 FPS, for 769 foot-pounds of energy.

The KAK 6.25″ barrel is a healthy step away from the edge, showing marked performance increases in velocity (naturally), accuracy (three groups in the 1-2 MOA range) and stabilization of subsonic rounds.  Supersonic rounds didn’t blow the charging handle back with each shot, nor was the concussive effect nearly as profound.

A few groups were wildly inaccurate, so I’ll be going over each upper to check assembly again.  Even a cheap barrel shouldn’t ever drop a 14 MOA group, so I’ll see if there’s anything mechanically incorrect.

I’ll keep working on this project as new barrels arrive (still waiting on Vertias/SLR upper and Modern Outfitters MC6-SD) and as opportunity permits more testing.  Next time I’ll be strapping on a much higher magnification optic, and as I’ll be shooting each barrels preffered ammo, groups should decrease on the whole.  Thanks for reading!

A special thanks to Discreet Ballistics, Ammo Inc, Fiocchi, and Federal for sending out ammo!  A similar thanks to V7, Right to Bear and KAK for sending barrels, gas blocks and rails.  Without their assistance, I couldn’t get an article like this off the ground.

-Rex Nanorum


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