Journey With The 300BlackOut

In 2011 Advanced Armament Corporation (AAC) introduced the 300 Blackout often referred to as the 300 BLK or 7.62x35mm. As I understand it through my research this cartridge was based off the 300 Whisper though interestingly enough there is no difference in the cartridge . The difference lies in the rifle chambers where the 300 Blackout chambers are a little longer than the 300 Whisper, and the lineage of the 300 Whisper began in 1990 by J. D. Jones who neck up a 221 Remington Fireball case to accept a .30 caliber.

According to Robert Silvers Development Director for AAC the 300 Blackout was created as a Low Visibility Carbine that’s as quiet as the MP5 with three times the distance.

  • Create a reliable compact 30-cal solution’s for AR platform
  •  Utilize existent inventory magazines while retaining their full capacity
    Create the optimal platform for sound and flash suppressed
  • Create compatible full power ammunition that matches 7.62×39 ballistics
    Work with subsonic and full power ammunition without requiring adjustable gas.
  • Provide the ability to penetrate barriers with high-mass projectiles
  • Provide all capabilities in a lightweight, durable, low recoiling package

When I originally heard about this new caliber it piqued my interest as its marketing was heavily towards delivering the same amount of energy as a 7.62×39 cartridge (AK47 round) on target with possibly increased accuracy by utilizing the AR15 platform. This cartridge uses all of the standard AR15 parts including the magazine with a simple .30cal barrel swap.

Most readers of Dayattherange visit for the unbiased reviews. This page is not intended to be a review of the rifles chambered for this cartridge or the cartridge itself. This is meant to be a journal of sorts of my endeavors, experience and fun I have had with the 300 Blackout cartridge. On this page you will undoubtedly find reloading information. This data is not intended to replace the appropriate reloading manuals data and should not be used without verifying and double checking the loads between two different official published reference points — IE reloading manuals. If you elect to utilize any of this data it is at your own risk.

Make sure to check back often as I have fully committed myself to document my 300 Blackout range adventures an update this page along way.

Though this cartridge piqued my interest I was not willing to add another caliber to the reloading stable or invest in a rifle until Darrel my long time friend and shooting partner was able to sneak this out to the range one day and had it sitting on the bench when I arrived. A Remington Model 7 in 300 Blackout. Though it is not your average Model 7 this one has an Olive Drab Green Cerakote finish and has a Yankee Hill QD Flash Suppressor which makes for easy installing of the Yankee Hill Phantom Sound Suppressor. It is also topped with a Nikon P-300 Blackout Scope.  After the first few rounds of subsonic rounds being fired and the sound of the thump of the 220gr bullet hitting the backstop seeming to be louder than the initial firing it was hard for me to hide my excitement. I didn’t want to get to overly excited as I did not want to be an accomplice to the wife beating he was surely going to get. I figured if he tried to sneak one by me then he had definitely snuck this one in the house past the wife. It is bad and scary enough my wife has threatened to taze both of us.

Darrel knew I was a little reluctant to add another caliber to the stable but we have been friends for so long that he also knows I am a sucker for a set of well made dies. So he handed these over to me with a sinister sort of grin on his face.

After the initial couple of range sessions our 300 Blackout journey would be cut a little short due to some over pressure concerns with Remington ammunition. Unfortunately for us the Remington plant was closed for the last part of the year due to the Holidays to try and address these concerns with them. After a number of emails and a call to the 1-800 support number they would finally get back with me months later asking for the ammunition in return providing all required shipping labels. The ammunition in question was Remington 115gr 300 Blackout ammunition which was popping primers and making for stiff extraction. This was the only ammunition which exhibited this behavior, with other brands of ammunition we did not experience this.

At the current time I am waiting to hear from Remington after sending the remainder of the ammunition back to them.

This minor set back would cause me to put the 300 Blackout dies into production right away. When it came to collecting brass for the 300blk I quickly figured out there was a number of ways to do so. You could make your own brass out of 223 brass by cutting the length of it down and necking it out to 30 caliber. You could also neck out 221 brass which is a lot quicker than the previous routine of cutting and sizing or you could just simply purchase brass as there are many manufacturers making factory brass as well as reforming old 223 brass. Darrell and I decided to utilize the last two methods for collecting our brass. Darrell purchased brass from West Desert Tactical and it turned out to be great brass reformed from 223 brass.


This brass is advertised as ready to load out of the packaging with primer pockets swaged. All of the brass was of the right dimensions but I chose to debur all of the cases first as the edge of the brass was a little sharp, this is more personal preference than anything. This brass most likely would have fired fine without the deburring step.

I on the other hand collected all of Darrell’s 221 brass. With my Redding National Match Competition Dies on hand I immediately started the re-sizing process only to figure out I did not have the right tools for the job. The case was requiring tremendous force and to keep from ruining such great dies or crushing the case I stopped the process, one thing I learned over 17 years ago when I started reloading was to never force your press. One quick call to Redding solved my problem. The dies I have do not have the tapered buttons required for this process, bummer not to fear Redding would have these parts in my hand within a few days.

The part numbers needed are 16276 tapered 270cal button and 16301 tapered 30cal button. These buttons would screw right into my resizing die with no issues and they were of very good quality.

270 and .30 Cal Expander

270 and .30 Cal Expander

One thing I notice was the smoothness of the buttons, it was almost as if they had some sort of grease on them already but they hadn’t. If you were to buy the Redding 300-221 die both of these buttons come with the die and aren’t needed. By now you have probably figure out that resizing the 221 brass to 300blk is a two step process, from 270 to 30cal. This must have been the original way J.D Jones started.

Die with the original button on it and the two new buttons


Here is what the original 221 cases (two on the left) look like next to a 300blk case.


You start with the original 270 button and very little lube so you don’t dent the cases, it doesn’t take much and I experimented with both RCBS pad lube as well as the Hornady case wax lube and ended up using the Hornady case wax it seemed to require less force.


Here is what the 221 brass (two on the left) look like after being necked out to 270cal next to the 300blk brass.


After batch neck sizing all of the brass to 270cal I then installed the 30cal button.


On my first 30cal neck sizing I noticed more force was needed and felt again something was not right. I did not have the expander button/rod deep enough into the seating die once correcting this slight flaw I was back in business though on this first case I did dent the shoulder a little due to adding more case wax, to much lube. There is no need to add any additional lube/wax to the 30cal neck sizing step there will be plenty left on the cases from the first step to get the job done.

Here is the finished product of 221 brass (two on the left) after being necked out to 270cal then 30cal sitting next to a preformed 300blk case from West Desert Tactical.


After the necking out process the 221 brass was a little long and out of SAAMI spec for 300blk so it will need to be trimmed. Once trimmed it can be primed loaded and fired.

The tools used for this job are

RCBS Rock Chucker, Redding Competition Die Set, 270cal tapered button part#16276, 30cal tapered button part#16301 and Hornady Case Wax.


I spent a lot of time reading material on in the reloading section looking at loading information. Yet I was also aware that there were many publications with 300Blk information had been published, Hodgdon’s 2012 Annual Magazine has a great article on this cartridge. Though I was a little amazed that Hodgdon allowed the author to publish his loads as many were over max of what was published in the back of the same manual. There is also data published in Hornady #9, Sierra #5 ( and Nosler #7 all of these manuals have a spot on my book shelf.


My research also told me that powders in the same burn rate range as A5744 and A1680 were the most appropriate for the 300Blk application. A5744 and A1680 were extremely difficult to find but I wanted to start there before experimenting with any other powders. Luckily I was able to get in contact with Jeff of JRS reloading and wouldn’t you know he had the powders I needed and ensured me he would put some aside for me at the next gun show. So my first go at reloading 300Blk would be with A5744 10.6gr and 220gr Sierra Match King utilizing Accurate reloading data. This turned out to be not as accurate as I would have liked.

This load was also verified on a RCBS 505 balance beam scale.

Though very quiet in the Model 7 Remington the accuracy was not as great — as I stated previously. We also had some troubles with the rounds chambering in the Model 7 Remington which really confused me as I had run all of these rounds through a Wilson case gauge.

Ok back to the drawing board. After more research on I found that the Wilson Gauge was only good for overall length. If you really wanted to be sure about your 300Blk rounds they need to be tested in a Sheridan case gauge. This gauge was made to mimic the minimal specification of a 300Blk chamber. Not only that it has a very nice cut out so that you can mimic seeing inside of the chamber. After receiving what I consider to be the best made chamber gauge I have ever seen in 20 years of shooting I decided to test all of the empty brass by first chambering them in the Wilson gauge and then with the Sheridan. Sure enough I would find that all of the cases would fit in the Wilson but none of them would fit in the Sheridan. Closer examination showed that after these cases were formed from 223 brass by being cut with a chop saw that they had an outside burr on them which when measured by my calipers made the brass slightly out of spec.


This is a Wilson gauge on a Sheridan manual showing what would lead you to believe the cases would chamber.


This is the Sheridan slotted gauge showing the same piece of brass was out of spec. Right away the Sheridan gauge was earning its keep as a necessary tool for my reloading bench. Again another minor set back. But with the amount of brass I had I would be again looking for a tool to make quick work of this chamfering and deburring work. I already had a Hornady Trio on the bench but it was a little slow for this work. Having a CTS power trimmer as part of my setup and loving it, which I reviewed here:

I would contact CTS Engineering and as luck would have it they did make a case prep tool that seemed as if it would meet my needs, and they were just putting the finishing touches on on their website which had some pictures of it.

Shortly after ordering I received my product and sure enough it was faster and more robust than the Hornady. It made short work of the 300Blk cases to get them all back in spec.

A few weeks later I was back on the bench working up other loads utilizing Magnum Pistol powder I had found in the Hornady #9 manual. I had not used up all of my accurate powder yet but I felt like I had to find something else that would work considering how hard Accurate powder is to find in my neck of the woods. I settled on H110 which I had plenty of considering how much I love big bore revolvers like the 44Mags, 460S&W and 500S&W magnums. But this time I was after supersonic loads that would function in Darrel’s newly acquired 300Blk AR15 with a stainless Wilson barrel 1/8 Twist on a Rock River lower.

Accuracy was not as good as I had expected it, but on this day we would again run into another small setback. We found that none of these loads would fully cycle Darrel’s AR system. The bolt would short cycle to not pick up the next round out of the magazine. It seemed as if there was not enough gas to operate the bolt. Again back to the drawing board. After further reading it seems the gas port diameter size is essential with the 300Blk. I found a number of articles stating on carbine length gas systems that the gas port would have to be enlarged by drilling it out. I also found a number of articles telling everyone to ensure the gas block was properly aligned. I was hoping the second remedy would be the fix for Darrel’s rifle because in no way was I willing to drill the gas port on a brand new upper. I must be doing something right because this time luck was on my side. As I disassembled Darrell’s AR upper and removed the gas port it seemed as if possibly it was misaligned.


I realigned and used a little blue locktite on the gas block screws and would assemble a few rounds and head to the range for some quick testing. Sure enough it works and cycles using rounds it had not cycled with previously.

This setup was one that would eventually push me over the edge and make me start to order all the parts for my first AR build.

Stay tuned for more to come. Time to build my first AR and it would be based on the 300Blackout cartridge.

Continued on 300Blackout Journey Page2