Ssshhhhhh, whisper, 300BlackOut

300 BlackOut, 300BLK or the metric designation is 7.62x35mm.

A unique design not so new or recently created. This often appears with cartridges as similar configurations have been experimented with in the past, as with some the 300 BlackOut is all about timing the introduction. (or a cartridge before it’s time) Similar to the 25.06 Remington a mild round until the development and introduction of slow burning powders like H4831, then the cartridge was noticed to be a big performer.


300 BlackOut loaded with a 168grain military pull down FMJBT. Velocity a mere 1700fps.


Newer powders, sub-sonic rounds and heavy bullets brought the 300 BlackOut to be noticed. Earlier developments didn’t take off as well, for example  The 8×35 Ribeyrolle was developed in 1917 during WW1 for the 1918 automatic carbine. The round is similar to the 300 BlackOut.



1969  a  7.62X28mm was developed, the round is similar to the 300 BlackOut.



1990   J. D. Jones developes  a 300 WHISPER
 to function in an ar15 platform upper. A barrel change will switch from 5.56 (223 rem) to 300 BlackOut all while operating with the same bolt and upper components and magazine.


The Whisper was originally developed from its parent case the .221 Fireball. It can be loaded to subsonic or supersonic velocities. This cartridge is almost exact to the BlackOut with minor dimensional  changes. The 300 BlackOut was created from this version and incorporates a longer neck.


2011 the 300 BlackOut was approved by SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute). With that support several commercial ammunition manufactures started loading for the round and firearms were chambered in 300 BlackOut. 300 Whisper commercial ammunition can be safely fired in a 300 BlackOut chamber due to the longer 300 BlackOut chamber throat, If you have any doubts contact the ammunition manufacturer or seek advice from your local gunsmith.



the 125 grain 300BLK will clock 2,215 feet per second with 1360 foot-pound force. The 220 grain subsonic round clocks at 1,010 feet per second with 498 foot-pound force. The round is good for out to 300 yards, but can reach 500 although not practical.  For short range the round will deliver high energy and hard hitting shots (Hog medicine). While shooting subsonic (220 grain) the energy is amazing for under 100 yards and it is quieter  than a 9mm whether suppressed or not. Because of this the round is great for short range CQB use which is good in combat situations. The timing was right with a big range in bullet weights (110 – 220 grain) available along with good powder selections. The 300 BlackOut became popular to the reloading community when ammo was scarce upon introduction of the round. Forming cases from 5.56 brass was common, cutting down and reforming to accept 30 caliber bullets however this brings up a very dangerous condition.


On the left is a 5.56 case, then cut at the shoulder, resized to 30 caliber, trimmed and on the right two 300 BlackOut cartridges. The danger is when an inexperienced shooter grabs some 300 BlackOut ammo and unknowingly chamber’s it in a 5.56/.223  chambered rifle. Yes it will chamber as the 30 caliber bullet will act as a false cartridge shoulder only to have dangerously high pressures resulting in exploded rifles and personal injury. Take some time and surf the web for this topic and you will see several cases of this! Know what ammo you are putting in any given firearm before chambering it!



300 BlackOut loaded in a 5.56/.223 magazine



The argument continues on whether the 300 BlackOut is superior to the 5.56/223. Down range energy, sustained subsonic velocity, lower recoil for heavier bullets and low suppressed sound for CQB situations. The cartridge fits a unique role as do other specialty cartridges, the 5.7×28 is a good example. You need to decide on the application of use, I find it a very interesting round as experimenting with powders and middle of weight spectrum bullets (168 grain) have proven it to be quite accurate. Another point to consider if you go the 300BLK route is gas port location, pistol and carbine are the choices.

Pistol length gas ports will cycle supersonic and subsonic ammo fine un-suppressed.

Carbine length will cycle supersonic while needing a suppressor to reliably cycle subsonic ammo.

Bullets for hunting need to be selected for low velocity expansion as most .308 bullets are designed for higher velocity cartridges. Several new designs are on the market allowing low (below 1500fps) reliable expansion rates with good primary wound cavity. For those of you that reload needing an expanding bullet look into these companies.

168 gr Rebated Boat Tail

img_20161016_105456    img_20161016_105414

As a wildcatter you can also make 300 BlackOut from 204 Ruger brass.


It’s October cooler weather is here and that should have you pulling out those safe queens and warming up some metal. New cartridges continue to be developed so don’t limit yourself to the mass-produced most commonly used ones. Get out and BlackOut! you just might like it.


Until next time be safe and burn some powder. It’s your second amendment right!


Right On Dead On All The Time



1 Comment

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One response to “Ssshhhhhh, whisper, 300BlackOut

  1. Hi thhanks for posting this

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